<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2021 Workiva-->
<!--r:e57f1b76-7f35-416a-b3eb-0fa6bf59a242,g:02684198-2eb8-4976-ae08-26c575b7e86f-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.supernus.com/role/CondensedConsolidatedStatementsofEarnings" xlink:type="simple" xlink:href="supn-20210630.xsd#CondensedConsolidatedStatementsofEarnings"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CondensedConsolidatedStatementsofEarnings" xlink:type="extended" id="i666c9a6ebfe444f489e12afdaa3fc6a9_CondensedConsolidatedStatementsofEarnings">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_3e1664b0-d51b-4dc8-a9f2-54ddf9e93fa6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_c16fdf3b-25ee-46ff-a012-20c071872334" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e1664b0-d51b-4dc8-a9f2-54ddf9e93fa6" xlink:to="loc_us-gaap_RevenuesAbstract_c16fdf3b-25ee-46ff-a012-20c071872334" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_9fe9eeb7-bf37-42a0-ba92-a790b73c6443" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_c16fdf3b-25ee-46ff-a012-20c071872334" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_9fe9eeb7-bf37-42a0-ba92-a790b73c6443" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_90278687-8c33-4be7-a50f-88da49a641e5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e1664b0-d51b-4dc8-a9f2-54ddf9e93fa6" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_90278687-8c33-4be7-a50f-88da49a641e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_f5a41271-7fc7-4511-ac35-60fa455b73ed" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_90278687-8c33-4be7-a50f-88da49a641e5" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_f5a41271-7fc7-4511-ac35-60fa455b73ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_0b232b1e-f7f8-4cc6-8541-9ffe55bceb47" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_90278687-8c33-4be7-a50f-88da49a641e5" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_0b232b1e-f7f8-4cc6-8541-9ffe55bceb47" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_6a1a5c5d-1adf-44cd-81b3-d13ac2ec41ff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_90278687-8c33-4be7-a50f-88da49a641e5" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_6a1a5c5d-1adf-44cd-81b3-d13ac2ec41ff" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_ae2af3de-73d1-4e83-a3a1-76bd1d7b2d1d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_90278687-8c33-4be7-a50f-88da49a641e5" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_ae2af3de-73d1-4e83-a3a1-76bd1d7b2d1d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_174a8fd6-58ce-4df3-8ec8-603673ad7060" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_90278687-8c33-4be7-a50f-88da49a641e5" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_174a8fd6-58ce-4df3-8ec8-603673ad7060" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_5d8acd3b-409f-41ab-87d8-d4293787ff1b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_90278687-8c33-4be7-a50f-88da49a641e5" xlink:to="loc_us-gaap_CostsAndExpenses_5d8acd3b-409f-41ab-87d8-d4293787ff1b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_21fc4527-62fc-4e55-85fb-b8a91c55638d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e1664b0-d51b-4dc8-a9f2-54ddf9e93fa6" xlink:to="loc_us-gaap_OperatingIncomeLoss_21fc4527-62fc-4e55-85fb-b8a91c55638d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_71dc3852-4bbc-4231-9b16-51b2533458ea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e1664b0-d51b-4dc8-a9f2-54ddf9e93fa6" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_71dc3852-4bbc-4231-9b16-51b2533458ea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpense_44b157c4-f393-4340-89a2-c24180d1cae6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_71dc3852-4bbc-4231-9b16-51b2533458ea" xlink:to="loc_us-gaap_InterestExpense_44b157c4-f393-4340-89a2-c24180d1cae6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_b24938d4-1433-440f-a454-918f1113a7db" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_71dc3852-4bbc-4231-9b16-51b2533458ea" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_b24938d4-1433-440f-a454-918f1113a7db" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_db2901a4-4f05-4683-83eb-fdfcfcfbdb60" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_71dc3852-4bbc-4231-9b16-51b2533458ea" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_db2901a4-4f05-4683-83eb-fdfcfcfbdb60" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_c1910096-2405-4d21-8ec7-2da90051a210" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e1664b0-d51b-4dc8-a9f2-54ddf9e93fa6" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_c1910096-2405-4d21-8ec7-2da90051a210" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_f80ed702-ef2f-4ec3-a9c5-ab9f9a619db6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e1664b0-d51b-4dc8-a9f2-54ddf9e93fa6" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_f80ed702-ef2f-4ec3-a9c5-ab9f9a619db6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_2c99f9d3-d18f-4f7f-94f2-2c3f565ef462" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e1664b0-d51b-4dc8-a9f2-54ddf9e93fa6" xlink:to="loc_us-gaap_NetIncomeLoss_2c99f9d3-d18f-4f7f-94f2-2c3f565ef462" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_983e48c9-4f9d-4fc5-9b10-42f633a711c4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareBasicAndDilutedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e1664b0-d51b-4dc8-a9f2-54ddf9e93fa6" xlink:to="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_983e48c9-4f9d-4fc5-9b10-42f633a711c4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_9bc9d985-2009-451a-a59a-0709be6e6b58" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_983e48c9-4f9d-4fc5-9b10-42f633a711c4" xlink:to="loc_us-gaap_EarningsPerShareBasic_9bc9d985-2009-451a-a59a-0709be6e6b58" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_63cacfdf-ef8f-4cd6-90ac-f0f96501cf5f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_983e48c9-4f9d-4fc5-9b10-42f633a711c4" xlink:to="loc_us-gaap_EarningsPerShareDiluted_63cacfdf-ef8f-4cd6-90ac-f0f96501cf5f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_8056cf88-dbde-455e-b10f-f81035a6f0e8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_3e1664b0-d51b-4dc8-a9f2-54ddf9e93fa6" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_8056cf88-dbde-455e-b10f-f81035a6f0e8" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_adbb5976-173f-414b-96eb-5cf34d009975" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_8056cf88-dbde-455e-b10f-f81035a6f0e8" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_adbb5976-173f-414b-96eb-5cf34d009975" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_6da6217d-d19d-4372-b80a-46f404f77e2b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_8056cf88-dbde-455e-b10f-f81035a6f0e8" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_6da6217d-d19d-4372-b80a-46f404f77e2b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_39056185-ab46-48ec-8d01-ff01ff16362e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_3e1664b0-d51b-4dc8-a9f2-54ddf9e93fa6" xlink:to="loc_us-gaap_StatementTable_39056185-ab46-48ec-8d01-ff01ff16362e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_696a0b66-2af7-4611-b74c-c4d35299b01c" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_39056185-ab46-48ec-8d01-ff01ff16362e" xlink:to="loc_srt_ProductOrServiceAxis_696a0b66-2af7-4611-b74c-c4d35299b01c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_696a0b66-2af7-4611-b74c-c4d35299b01c_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_696a0b66-2af7-4611-b74c-c4d35299b01c" xlink:to="loc_srt_ProductsAndServicesDomain_696a0b66-2af7-4611-b74c-c4d35299b01c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_92a542b6-6d0b-479f-998d-458c2d7230c4" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_696a0b66-2af7-4611-b74c-c4d35299b01c" xlink:to="loc_srt_ProductsAndServicesDomain_92a542b6-6d0b-479f-998d-458c2d7230c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_cd236228-fe2c-46af-b3de-baf35af2cbd8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_92a542b6-6d0b-479f-998d-458c2d7230c4" xlink:to="loc_us-gaap_ProductMember_cd236228-fe2c-46af-b3de-baf35af2cbd8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RoyaltyMember_c3c9d613-9460-481d-aa63-3d0988ba8338" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RoyaltyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_92a542b6-6d0b-479f-998d-458c2d7230c4" xlink:to="loc_us-gaap_RoyaltyMember_c3c9d613-9460-481d-aa63-3d0988ba8338" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/CondensedConsolidatedStatementsofChangesinStockholdersEquity" xlink:type="simple" xlink:href="supn-20210630.xsd#CondensedConsolidatedStatementsofChangesinStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CondensedConsolidatedStatementsofChangesinStockholdersEquity" xlink:type="extended" id="i464ec5ed532d43afa8d033917aaf00c3_CondensedConsolidatedStatementsofChangesinStockholdersEquity">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_a27e246a-1d22-4a60-a090-933129ab0587" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d53df1c4-bac5-416f-9111-87c3d63afc0a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_a27e246a-1d22-4a60-a090-933129ab0587" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d53df1c4-bac5-416f-9111-87c3d63afc0a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_8b208617-0eb3-451e-8f97-92d2e37e4299" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d53df1c4-bac5-416f-9111-87c3d63afc0a" xlink:to="loc_us-gaap_SharesOutstanding_8b208617-0eb3-451e-8f97-92d2e37e4299" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_dc96cd0e-2b69-4468-a026-46ded444a46a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d53df1c4-bac5-416f-9111-87c3d63afc0a" xlink:to="loc_us-gaap_StockholdersEquity_dc96cd0e-2b69-4468-a026-46ded444a46a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_9f660935-b144-449f-a24f-1cc5814bdcad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d53df1c4-bac5-416f-9111-87c3d63afc0a" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_9f660935-b144-449f-a24f-1cc5814bdcad" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_a40ffd32-ae29-4a83-890a-5d898e93a7f5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d53df1c4-bac5-416f-9111-87c3d63afc0a" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_a40ffd32-ae29-4a83-890a-5d898e93a7f5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_51e87efb-0891-4155-baf2-89d2cb996f87" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d53df1c4-bac5-416f-9111-87c3d63afc0a" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_51e87efb-0891-4155-baf2-89d2cb996f87" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_67248aea-17e7-47d9-8d7a-03e76b704474" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d53df1c4-bac5-416f-9111-87c3d63afc0a" xlink:to="loc_us-gaap_NetIncomeLoss_67248aea-17e7-47d9-8d7a-03e76b704474" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent_aa64cf3e-016d-4d44-9442-3dcb4a7ed124" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_d53df1c4-bac5-416f-9111-87c3d63afc0a" xlink:to="loc_us-gaap_OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent_aa64cf3e-016d-4d44-9442-3dcb4a7ed124" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_2210dffc-7225-43c0-8aa3-a18a794ff3dd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_13db4704-b330-4ca3-9ea9-ec8b08f7e240" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_755d74f5-2bb7-4ff3-8e80-5d902ee8ce90" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_a27e246a-1d22-4a60-a090-933129ab0587" xlink:to="loc_us-gaap_StatementTable_755d74f5-2bb7-4ff3-8e80-5d902ee8ce90" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_c80c487d-7650-491d-8601-e79fd8b367e9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_755d74f5-2bb7-4ff3-8e80-5d902ee8ce90" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_c80c487d-7650-491d-8601-e79fd8b367e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_c80c487d-7650-491d-8601-e79fd8b367e9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_c80c487d-7650-491d-8601-e79fd8b367e9" xlink:to="loc_us-gaap_EquityComponentDomain_c80c487d-7650-491d-8601-e79fd8b367e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_b0c5f31c-bd86-45dc-b887-08c1cebd549a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_c80c487d-7650-491d-8601-e79fd8b367e9" xlink:to="loc_us-gaap_EquityComponentDomain_b0c5f31c-bd86-45dc-b887-08c1cebd549a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_aac6f563-4eda-4d74-b2e3-904996db54c6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b0c5f31c-bd86-45dc-b887-08c1cebd549a" xlink:to="loc_us-gaap_CommonStockMember_aac6f563-4eda-4d74-b2e3-904996db54c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_e482e99a-6b24-46ea-bfdf-cc5884bf3343" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b0c5f31c-bd86-45dc-b887-08c1cebd549a" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_e482e99a-6b24-46ea-bfdf-cc5884bf3343" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_a1e9af14-1e82-4d59-97d5-239aa5478b05" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b0c5f31c-bd86-45dc-b887-08c1cebd549a" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_a1e9af14-1e82-4d59-97d5-239aa5478b05" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_5c58e4c1-7459-474d-a1d4-01176bf28fef" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b0c5f31c-bd86-45dc-b887-08c1cebd549a" xlink:to="loc_us-gaap_RetainedEarningsMember_5c58e4c1-7459-474d-a1d4-01176bf28fef" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/USWMAcquisitionNarrativeDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#USWMAcquisitionNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/USWMAcquisitionNarrativeDetails" xlink:type="extended" id="i39273d406cc64cff9d0712df721001e1_USWMAcquisitionNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_2eaa5a08-b82f-4c26-bb6d-9a51bd762ba1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_5b89e9f7-1be3-4744-8282-b4017a98686c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_2eaa5a08-b82f-4c26-bb6d-9a51bd762ba1" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_5b89e9f7-1be3-4744-8282-b4017a98686c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_1d2f474c-3941-423b-be65-57067e8c0b9d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_2eaa5a08-b82f-4c26-bb6d-9a51bd762ba1" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_1d2f474c-3941-423b-be65-57067e8c0b9d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInTheRangeOfOutcomesContingentConsiderationLiabilityValueHigh_52f58695-cd8f-40d4-984b-1634412c4560" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInTheRangeOfOutcomesContingentConsiderationLiabilityValueHigh"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_2eaa5a08-b82f-4c26-bb6d-9a51bd762ba1" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInTheRangeOfOutcomesContingentConsiderationLiabilityValueHigh_52f58695-cd8f-40d4-984b-1634412c4560" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_PaymentsToAcquireBusinessesNetOfCashAcquiredAdditionalPayable_eecea81a-ce9c-48af-b69f-3a435bc0af80" xlink:href="supn-20210630.xsd#supn_PaymentsToAcquireBusinessesNetOfCashAcquiredAdditionalPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_2eaa5a08-b82f-4c26-bb6d-9a51bd762ba1" xlink:to="loc_supn_PaymentsToAcquireBusinessesNetOfCashAcquiredAdditionalPayable_eecea81a-ce9c-48af-b69f-3a435bc0af80" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueLow_51f1282e-492a-4d45-a428-eb3b222bbb82" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueLow"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_2eaa5a08-b82f-4c26-bb6d-9a51bd762ba1" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueLow_51f1282e-492a-4d45-a428-eb3b222bbb82" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_19c3b7ed-ca03-4697-a95e-807bb35436de" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_2eaa5a08-b82f-4c26-bb6d-9a51bd762ba1" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_19c3b7ed-ca03-4697-a95e-807bb35436de" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_82fd0091-8499-44e7-8945-96475aaea859" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_2eaa5a08-b82f-4c26-bb6d-9a51bd762ba1" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_82fd0091-8499-44e7-8945-96475aaea859" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentInventory_0794e8d9-da11-4cef-8293-56c6bb08557b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_2eaa5a08-b82f-4c26-bb6d-9a51bd762ba1" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentInventory_0794e8d9-da11-4cef-8293-56c6bb08557b" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_3c3c613c-5ddd-45e3-a7fb-a87e706706ea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_2eaa5a08-b82f-4c26-bb6d-9a51bd762ba1" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_3c3c613c-5ddd-45e3-a7fb-a87e706706ea" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIntangibles_9cc034a4-3ea4-473f-b0b0-5b69dfebc0bc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_2eaa5a08-b82f-4c26-bb6d-9a51bd762ba1" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIntangibles_9cc034a4-3ea4-473f-b0b0-5b69dfebc0bc" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentInventory_b006064b-f47e-47dc-a13c-5d0bce12891e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentInventory"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8680e974-2c9a-428c-b321-c748c282b439" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_2eaa5a08-b82f-4c26-bb6d-9a51bd762ba1" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8680e974-2c9a-428c-b321-c748c282b439" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_1b1dc3d9-db40-46ef-826a-a66b8abbde73" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8680e974-2c9a-428c-b321-c748c282b439" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_1b1dc3d9-db40-46ef-826a-a66b8abbde73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_1b1dc3d9-db40-46ef-826a-a66b8abbde73_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_1b1dc3d9-db40-46ef-826a-a66b8abbde73" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_1b1dc3d9-db40-46ef-826a-a66b8abbde73_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_bd703215-773e-423a-aa20-c95a2eaaca42" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_1b1dc3d9-db40-46ef-826a-a66b8abbde73" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_bd703215-773e-423a-aa20-c95a2eaaca42" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_cdcdc3fb-e602-42ea-8200-a623a7d2d613" xlink:href="supn-20210630.xsd#supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_bd703215-773e-423a-aa20-c95a2eaaca42" xlink:to="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_cdcdc3fb-e602-42ea-8200-a623a7d2d613" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationByTypeAxis_1b79bf39-1849-4408-b0e7-4bb4f5d4415e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContingentConsiderationByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8680e974-2c9a-428c-b321-c748c282b439" xlink:to="loc_us-gaap_ContingentConsiderationByTypeAxis_1b79bf39-1849-4408-b0e7-4bb4f5d4415e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_1b79bf39-1849-4408-b0e7-4bb4f5d4415e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_1b79bf39-1849-4408-b0e7-4bb4f5d4415e" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_1b79bf39-1849-4408-b0e7-4bb4f5d4415e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_fc64a8a3-d7e2-4820-b7a7-cd7205bda34b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_1b79bf39-1849-4408-b0e7-4bb4f5d4415e" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_fc64a8a3-d7e2-4820-b7a7-cd7205bda34b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_SPN830RegulatoryAndCommercialActivitiesMember_3dbd5748-8241-46c4-8aee-8e8f660b58e5" xlink:href="supn-20210630.xsd#supn_SPN830RegulatoryAndCommercialActivitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_fc64a8a3-d7e2-4820-b7a7-cd7205bda34b" xlink:to="loc_supn_SPN830RegulatoryAndCommercialActivitiesMember_3dbd5748-8241-46c4-8aee-8e8f660b58e5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_SPN830FutureSalesPerformanceMember_9ea345e9-cc2b-40e4-827a-9e5713bcda8f" xlink:href="supn-20210630.xsd#supn_SPN830FutureSalesPerformanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_fc64a8a3-d7e2-4820-b7a7-cd7205bda34b" xlink:to="loc_supn_SPN830FutureSalesPerformanceMember_9ea345e9-cc2b-40e4-827a-9e5713bcda8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_SPN830FDAAcceptanceMilestoneMember_f7354b65-8b4f-4d66-ae5c-040a07f4495b" xlink:href="supn-20210630.xsd#supn_SPN830FDAAcceptanceMilestoneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_fc64a8a3-d7e2-4820-b7a7-cd7205bda34b" xlink:to="loc_supn_SPN830FDAAcceptanceMilestoneMember_f7354b65-8b4f-4d66-ae5c-040a07f4495b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_SPN830NDAApprovalMilestoneMember_65d30bdc-b2ad-4561-81e2-3a93a66144f5" xlink:href="supn-20210630.xsd#supn_SPN830NDAApprovalMilestoneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_fc64a8a3-d7e2-4820-b7a7-cd7205bda34b" xlink:to="loc_supn_SPN830NDAApprovalMilestoneMember_65d30bdc-b2ad-4561-81e2-3a93a66144f5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_SPN830FirstCommercialAndSaleMember_5bc77da2-7d7f-4f61-8edd-30951954af5e" xlink:href="supn-20210630.xsd#supn_SPN830FirstCommercialAndSaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_fc64a8a3-d7e2-4820-b7a7-cd7205bda34b" xlink:to="loc_supn_SPN830FirstCommercialAndSaleMember_5bc77da2-7d7f-4f61-8edd-30951954af5e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_APOKYNMember_cdeee757-5be8-476c-90ad-7a875759cf1d" xlink:href="supn-20210630.xsd#supn_APOKYNMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_fc64a8a3-d7e2-4820-b7a7-cd7205bda34b" xlink:to="loc_supn_APOKYNMember_cdeee757-5be8-476c-90ad-7a875759cf1d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_APOKYNAndSPN830Member_8f6b5d4f-0f10-4818-ae1e-28547b463886" xlink:href="supn-20210630.xsd#supn_APOKYNAndSPN830Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_fc64a8a3-d7e2-4820-b7a7-cd7205bda34b" xlink:to="loc_supn_APOKYNAndSPN830Member_8f6b5d4f-0f10-4818-ae1e-28547b463886" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_180e4602-24e6-4bf9-8adc-ae06cdef423f" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8680e974-2c9a-428c-b321-c748c282b439" xlink:to="loc_srt_RestatementAxis_180e4602-24e6-4bf9-8adc-ae06cdef423f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_180e4602-24e6-4bf9-8adc-ae06cdef423f_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_180e4602-24e6-4bf9-8adc-ae06cdef423f" xlink:to="loc_srt_RestatementDomain_180e4602-24e6-4bf9-8adc-ae06cdef423f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_f5a9198d-56f3-4e34-afb5-8d26ec85e098" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_180e4602-24e6-4bf9-8adc-ae06cdef423f" xlink:to="loc_srt_RestatementDomain_f5a9198d-56f3-4e34-afb5-8d26ec85e098" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioPreviouslyReportedMember_1d5db20a-4205-45ff-9ea1-69c3bb28f2bd" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ScenarioPreviouslyReportedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_f5a9198d-56f3-4e34-afb5-8d26ec85e098" xlink:to="loc_srt_ScenarioPreviouslyReportedMember_1d5db20a-4205-45ff-9ea1-69c3bb28f2bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_864879ca-1df4-4668-af0d-b2391f0d3b71" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_8680e974-2c9a-428c-b321-c748c282b439" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_864879ca-1df4-4668-af0d-b2391f0d3b71" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_864879ca-1df4-4668-af0d-b2391f0d3b71_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_864879ca-1df4-4668-af0d-b2391f0d3b71" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_864879ca-1df4-4668-af0d-b2391f0d3b71_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_7df8d9e9-da36-48d4-9281-8900387b4804" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_864879ca-1df4-4668-af0d-b2391f0d3b71" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_7df8d9e9-da36-48d4-9281-8900387b4804" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InProcessResearchAndDevelopmentMember_43ff1526-cdcd-46f9-adf5-baf9d70e730f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InProcessResearchAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_7df8d9e9-da36-48d4-9281-8900387b4804" xlink:to="loc_us-gaap_InProcessResearchAndDevelopmentMember_43ff1526-cdcd-46f9-adf5-baf9d70e730f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_c1dbb66e-3dad-487c-8fb1-453bcc37f67c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_7df8d9e9-da36-48d4-9281-8900387b4804" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_c1dbb66e-3dad-487c-8fb1-453bcc37f67c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/USWMAcquisitionPurchasePriceConsiderationDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#USWMAcquisitionPurchasePriceConsiderationDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/USWMAcquisitionPurchasePriceConsiderationDetails" xlink:type="extended" id="ic45ec1a7c1cd4de0ba5204c26e1328cb_USWMAcquisitionPurchasePriceConsiderationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_44971a25-fcd5-4df3-bf01-63b02eed6efe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_dfeab729-c57a-4782-9059-b25f05cc202a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_44971a25-fcd5-4df3-bf01-63b02eed6efe" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_dfeab729-c57a-4782-9059-b25f05cc202a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_9a69d488-6fd4-4a6b-b429-709518cfe11d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_44971a25-fcd5-4df3-bf01-63b02eed6efe" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_9a69d488-6fd4-4a6b-b429-709518cfe11d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_ce631617-476a-4e0e-b214-3ce2e87fae85" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_44971a25-fcd5-4df3-bf01-63b02eed6efe" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_ce631617-476a-4e0e-b214-3ce2e87fae85" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_33fc88b1-d2c0-4787-8d8b-1ca00c0c1776" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_44971a25-fcd5-4df3-bf01-63b02eed6efe" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_33fc88b1-d2c0-4787-8d8b-1ca00c0c1776" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_49c22522-514c-4e45-8784-2ce794d5812c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_44971a25-fcd5-4df3-bf01-63b02eed6efe" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_49c22522-514c-4e45-8784-2ce794d5812c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCashConsiderationTransferred_240ba00c-c101-4b1b-bb5d-52531190327d" xlink:href="supn-20210630.xsd#supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCashConsiderationTransferred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_49c22522-514c-4e45-8784-2ce794d5812c" xlink:to="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentCashConsiderationTransferred_240ba00c-c101-4b1b-bb5d-52531190327d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_a0e23777-9545-43ec-87c2-6ca9cc201d45" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_49c22522-514c-4e45-8784-2ce794d5812c" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_a0e23777-9545-43ec-87c2-6ca9cc201d45" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred_46c83c43-914e-49cc-a9fd-d7f1c10e3c37" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_49c22522-514c-4e45-8784-2ce794d5812c" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred_46c83c43-914e-49cc-a9fd-d7f1c10e3c37" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferredCash_9e4f58db-4a59-48ec-84c7-5ef6c2cc9129" xlink:href="supn-20210630.xsd#supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferredCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_49c22522-514c-4e45-8784-2ce794d5812c" xlink:to="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferredCash_9e4f58db-4a59-48ec-84c7-5ef6c2cc9129" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_1386ac3f-8b8d-45a8-9c76-ac9a3c6de750" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_44971a25-fcd5-4df3-bf01-63b02eed6efe" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_1386ac3f-8b8d-45a8-9c76-ac9a3c6de750" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_69e629b7-e63e-4df3-9cc5-bc8ce5e8f5ec" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_1386ac3f-8b8d-45a8-9c76-ac9a3c6de750" xlink:to="loc_srt_RestatementAxis_69e629b7-e63e-4df3-9cc5-bc8ce5e8f5ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_69e629b7-e63e-4df3-9cc5-bc8ce5e8f5ec_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_69e629b7-e63e-4df3-9cc5-bc8ce5e8f5ec" xlink:to="loc_srt_RestatementDomain_69e629b7-e63e-4df3-9cc5-bc8ce5e8f5ec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_0e355a4f-2918-421c-a65c-f9eca837d881" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_69e629b7-e63e-4df3-9cc5-bc8ce5e8f5ec" xlink:to="loc_srt_RestatementDomain_0e355a4f-2918-421c-a65c-f9eca837d881" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioPreviouslyReportedMember_7c3c6146-29b4-4882-99b7-3abd4728beae" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ScenarioPreviouslyReportedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_0e355a4f-2918-421c-a65c-f9eca837d881" xlink:to="loc_srt_ScenarioPreviouslyReportedMember_7c3c6146-29b4-4882-99b7-3abd4728beae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_cf530674-3809-4c40-8fce-bd88a71947b0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_1386ac3f-8b8d-45a8-9c76-ac9a3c6de750" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_cf530674-3809-4c40-8fce-bd88a71947b0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_cf530674-3809-4c40-8fce-bd88a71947b0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_cf530674-3809-4c40-8fce-bd88a71947b0" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_cf530674-3809-4c40-8fce-bd88a71947b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e9e468c9-4b40-4f11-8301-1ba4f106d9bd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_cf530674-3809-4c40-8fce-bd88a71947b0" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e9e468c9-4b40-4f11-8301-1ba4f106d9bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_0d25f6a4-cb27-48b6-8ed6-7979f827269e" xlink:href="supn-20210630.xsd#supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e9e468c9-4b40-4f11-8301-1ba4f106d9bd" xlink:to="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_0d25f6a4-cb27-48b6-8ed6-7979f827269e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/USWMAcquisitionScheduleofRecognizedIdentifiedAssetsAcquiredandLiabilitiesAssumedDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#USWMAcquisitionScheduleofRecognizedIdentifiedAssetsAcquiredandLiabilitiesAssumedDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/USWMAcquisitionScheduleofRecognizedIdentifiedAssetsAcquiredandLiabilitiesAssumedDetails" xlink:type="extended" id="i36bc8ba4824446d5bac404e2a4e22584_USWMAcquisitionScheduleofRecognizedIdentifiedAssetsAcquiredandLiabilitiesAssumedDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_06f8a998-8b9c-4c36-800b-57e15f56a588" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents_06f8a998-8b9c-4c36-800b-57e15f56a588" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_ae66120d-3fc7-4ed6-9127-48e67a451587" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_ae66120d-3fc7-4ed6-9127-48e67a451587" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_8de6a409-2eef-44a0-bf21-33015682fd09" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory_8de6a409-2eef-44a0-bf21-33015682fd09" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_5b08e1ab-1c98-4e2c-bbd9-cee452dbff19" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_5b08e1ab-1c98-4e2c-bbd9-cee452dbff19" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_95f35ad8-8105-45c0-acf4-0e2edb9461ff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_95f35ad8-8105-45c0-acf4-0e2edb9461ff" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinancingLeaseRightOfUseAsset_5f251540-064a-4b01-822c-80617aabf3d2" xlink:href="supn-20210630.xsd#supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinancingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinancingLeaseRightOfUseAsset_5f251540-064a-4b01-822c-80617aabf3d2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAsset_00e94ceb-bf4a-4e60-a63a-efa13a1d115b" xlink:href="supn-20210630.xsd#supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseRightOfUseAsset_00e94ceb-bf4a-4e60-a63a-efa13a1d115b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_19edba2a-32ed-4e91-97e7-312bc62b0b78" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_19edba2a-32ed-4e91-97e7-312bc62b0b78" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_ac850a8e-782c-4e70-9ac8-e510780df504" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_ac850a8e-782c-4e70-9ac8-e510780df504" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAcquired_fcd9ccf8-4181-4631-86cc-b02a6ccc9989" xlink:href="supn-20210630.xsd#supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAcquired_fcd9ccf8-4181-4631-86cc-b02a6ccc9989" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_c395cd03-5887-454a-be97-37bb189ce6b0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_c395cd03-5887-454a-be97-37bb189ce6b0" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedExpensesAndOtherCurrentLiabilities_64871db5-666c-4f44-9b3c-9475b757dea5" xlink:href="supn-20210630.xsd#supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedExpensesAndOtherCurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAccruedExpensesAndOtherCurrentLiabilities_64871db5-666c-4f44-9b3c-9475b757dea5" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinanceLeaseLiability_3671cc6e-e866-4391-a282-6dfe9f9bd9f6" xlink:href="supn-20210630.xsd#supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinanceLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinanceLeaseLiability_3671cc6e-e866-4391-a282-6dfe9f9bd9f6" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseLiability_e62d0c41-d0da-4af0-bcfc-6c16be82f98e" xlink:href="supn-20210630.xsd#supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOperatingLeaseLiability_e62d0c41-d0da-4af0-bcfc-6c16be82f98e" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredIncomeTaxLiabilities_17f9b360-8348-4bfa-ac9d-138b3dc2eadd" xlink:href="supn-20210630.xsd#supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredIncomeTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_supn_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredIncomeTaxLiabilities_17f9b360-8348-4bfa-ac9d-138b3dc2eadd" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_787d1935-f83c-47c5-b1b8-2703c7c1cfaf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedLiabilities_787d1935-f83c-47c5-b1b8-2703c7c1cfaf" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_fb03fba2-28e4-417b-9bdc-b5adace437c9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet_fb03fba2-28e4-417b-9bdc-b5adace437c9" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_e30e00e2-20b9-4b49-a1f0-6c37deb31a69" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_us-gaap_Goodwill_e30e00e2-20b9-4b49-a1f0-6c37deb31a69" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_18730db9-f27b-4f8c-9ddc-4d47d7e64eca" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_18730db9-f27b-4f8c-9ddc-4d47d7e64eca" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_d50c1bc8-e5c2-4c52-bf2c-00a1079c92d4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_d50c1bc8-e5c2-4c52-bf2c-00a1079c92d4" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentInventory_88d80eb9-8d3a-4458-8036-b54d43ac2c41" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentInventory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_d50c1bc8-e5c2-4c52-bf2c-00a1079c92d4" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentInventory_88d80eb9-8d3a-4458-8036-b54d43ac2c41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentFinancingLeaseRightOfUseAssets_d6a5492b-46b5-4d5b-8c99-5aef803f90e7" xlink:href="supn-20210630.xsd#supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentFinancingLeaseRightOfUseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_d50c1bc8-e5c2-4c52-bf2c-00a1079c92d4" xlink:to="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentFinancingLeaseRightOfUseAssets_d6a5492b-46b5-4d5b-8c99-5aef803f90e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOperatingLeaseRightOfUseAssets_2146f8ef-db64-4c66-90fd-35c15228b9fe" xlink:href="supn-20210630.xsd#supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOperatingLeaseRightOfUseAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_d50c1bc8-e5c2-4c52-bf2c-00a1079c92d4" xlink:to="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOperatingLeaseRightOfUseAssets_2146f8ef-db64-4c66-90fd-35c15228b9fe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIntangibles_e7bb2420-1f61-4a27-8463-ba3fefd94f49" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIntangibles"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_d50c1bc8-e5c2-4c52-bf2c-00a1079c92d4" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentIntangibles_e7bb2420-1f61-4a27-8463-ba3fefd94f49" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAssets_b3957270-7440-4320-a404-a0410fdcf2dd" xlink:href="supn-20210630.xsd#supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_d50c1bc8-e5c2-4c52-bf2c-00a1079c92d4" xlink:to="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAssets_b3957270-7440-4320-a404-a0410fdcf2dd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentFinancingLeaseLiability_8e6e0bc9-b445-43a9-9414-2f5080ae3cb9" xlink:href="supn-20210630.xsd#supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentFinancingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_d50c1bc8-e5c2-4c52-bf2c-00a1079c92d4" xlink:to="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentFinancingLeaseLiability_8e6e0bc9-b445-43a9-9414-2f5080ae3cb9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOperatingLeaseLiability_7a962892-c344-453f-8a85-5f5aaeecf340" xlink:href="supn-20210630.xsd#supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOperatingLeaseLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_d50c1bc8-e5c2-4c52-bf2c-00a1079c92d4" xlink:to="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentOperatingLeaseLiability_7a962892-c344-453f-8a85-5f5aaeecf340" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredIncomeTaxLiabilities_fc75a6b3-1192-469e-bee7-c0de7797ce4e" xlink:href="supn-20210630.xsd#supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredIncomeTaxLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_d50c1bc8-e5c2-4c52-bf2c-00a1079c92d4" xlink:to="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentDeferredIncomeTaxLiabilities_fc75a6b3-1192-469e-bee7-c0de7797ce4e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentLiabilities_2982e4bc-94b2-4d68-8aff-7a3a5b45f3b1" xlink:href="supn-20210630.xsd#supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_d50c1bc8-e5c2-4c52-bf2c-00a1079c92d4" xlink:to="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentLiabilities_2982e4bc-94b2-4d68-8aff-7a3a5b45f3b1" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAssetsLiabilitiesNet_967555bf-b57c-47a6-9a28-4ed63e56d8f6" xlink:href="supn-20210630.xsd#supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAssetsLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_d50c1bc8-e5c2-4c52-bf2c-00a1079c92d4" xlink:to="loc_supn_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentAssetsLiabilitiesNet_967555bf-b57c-47a6-9a28-4ed63e56d8f6" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_b62a3f2c-2176-4dfe-adae-7a517c338ca2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_d50c1bc8-e5c2-4c52-bf2c-00a1079c92d4" xlink:to="loc_us-gaap_GoodwillPurchaseAccountingAdjustments_b62a3f2c-2176-4dfe-adae-7a517c338ca2" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred_f52959f2-7ffa-465c-b9fa-9be3fd7be610" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentsAbstract_d50c1bc8-e5c2-4c52-bf2c-00a1079c92d4" xlink:to="loc_us-gaap_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentConsiderationTransferred_f52959f2-7ffa-465c-b9fa-9be3fd7be610" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_ef91adc3-7625-43bb-a09f-bf42773fa304" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_078fe61a-2741-415c-95b8-6d4b610af1ad" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_ef91adc3-7625-43bb-a09f-bf42773fa304" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_3940c8f1-f2a9-4364-a800-284e132e8759" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_ef91adc3-7625-43bb-a09f-bf42773fa304" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_3940c8f1-f2a9-4364-a800-284e132e8759" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3940c8f1-f2a9-4364-a800-284e132e8759_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_3940c8f1-f2a9-4364-a800-284e132e8759" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3940c8f1-f2a9-4364-a800-284e132e8759_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2a8874c7-de09-4c61-8825-aaf9da21c42b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_3940c8f1-f2a9-4364-a800-284e132e8759" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2a8874c7-de09-4c61-8825-aaf9da21c42b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_10bfbf3f-ad3b-441e-919e-591a1eaf07da" xlink:href="supn-20210630.xsd#supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_2a8874c7-de09-4c61-8825-aaf9da21c42b" xlink:to="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_10bfbf3f-ad3b-441e-919e-591a1eaf07da" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementAxis_12649fd3-03a4-4263-ba2c-d3805592ef4b" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RestatementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_ef91adc3-7625-43bb-a09f-bf42773fa304" xlink:to="loc_srt_RestatementAxis_12649fd3-03a4-4263-ba2c-d3805592ef4b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_12649fd3-03a4-4263-ba2c-d3805592ef4b_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RestatementAxis_12649fd3-03a4-4263-ba2c-d3805592ef4b" xlink:to="loc_srt_RestatementDomain_12649fd3-03a4-4263-ba2c-d3805592ef4b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RestatementDomain_1e576962-33b3-487c-bf97-152ecf241b09" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RestatementDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RestatementAxis_12649fd3-03a4-4263-ba2c-d3805592ef4b" xlink:to="loc_srt_RestatementDomain_1e576962-33b3-487c-bf97-152ecf241b09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioPreviouslyReportedMember_135487b8-294a-4eee-9e0d-f10c7af378f6" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ScenarioPreviouslyReportedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RestatementDomain_1e576962-33b3-487c-bf97-152ecf241b09" xlink:to="loc_srt_ScenarioPreviouslyReportedMember_135487b8-294a-4eee-9e0d-f10c7af378f6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/USWMAcquisitionComponentsofIntangibleAssetsandEstimatedUsefulLivesDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#USWMAcquisitionComponentsofIntangibleAssetsandEstimatedUsefulLivesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/USWMAcquisitionComponentsofIntangibleAssetsandEstimatedUsefulLivesDetails" xlink:type="extended" id="i7ea943229cd7471dbfed0f8d099e2c69_USWMAcquisitionComponentsofIntangibleAssetsandEstimatedUsefulLivesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_60625172-26df-4913-8dd4-986ccf6d21a6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_4870ce18-3ff7-4b91-afd2-d5cbac8a64a6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_60625172-26df-4913-8dd4-986ccf6d21a6" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_4870ce18-3ff7-4b91-afd2-d5cbac8a64a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_c506ec9e-189a-4f20-b0e0-ac93ac2a4549" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_60625172-26df-4913-8dd4-986ccf6d21a6" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_c506ec9e-189a-4f20-b0e0-ac93ac2a4549" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_2f718b6b-9716-4130-a429-0d08e8cc6e7a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_60625172-26df-4913-8dd4-986ccf6d21a6" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_2f718b6b-9716-4130-a429-0d08e8cc6e7a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_5797cb60-4b31-433a-b076-4f7f4c6a682b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_2f718b6b-9716-4130-a429-0d08e8cc6e7a" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_5797cb60-4b31-433a-b076-4f7f4c6a682b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5797cb60-4b31-433a-b076-4f7f4c6a682b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_5797cb60-4b31-433a-b076-4f7f4c6a682b" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_5797cb60-4b31-433a-b076-4f7f4c6a682b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_14936547-17b3-441a-b87a-6774c6da7258" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_5797cb60-4b31-433a-b076-4f7f4c6a682b" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_14936547-17b3-441a-b87a-6774c6da7258" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_a8d4cf23-8e27-4a6e-b6ef-29ed3d23eec6" xlink:href="supn-20210630.xsd#supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_14936547-17b3-441a-b87a-6774c6da7258" xlink:to="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_a8d4cf23-8e27-4a6e-b6ef-29ed3d23eec6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e7f25edb-a28b-46d7-b4e8-ead36648d142" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_2f718b6b-9716-4130-a429-0d08e8cc6e7a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e7f25edb-a28b-46d7-b4e8-ead36648d142" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e7f25edb-a28b-46d7-b4e8-ead36648d142_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e7f25edb-a28b-46d7-b4e8-ead36648d142" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e7f25edb-a28b-46d7-b4e8-ead36648d142_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_7f350601-2f0e-49f7-b21f-285eb29df825" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_e7f25edb-a28b-46d7-b4e8-ead36648d142" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_7f350601-2f0e-49f7-b21f-285eb29df825" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InProcessResearchAndDevelopmentMember_e5f398a7-e767-462a-9507-87832ff40a27" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InProcessResearchAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_7f350601-2f0e-49f7-b21f-285eb29df825" xlink:to="loc_us-gaap_InProcessResearchAndDevelopmentMember_e5f398a7-e767-462a-9507-87832ff40a27" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_15e3b5a7-77b9-452f-abc7-f9c13c386b94" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_7f350601-2f0e-49f7-b21f-285eb29df825" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_15e3b5a7-77b9-452f-abc7-f9c13c386b94" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_c75b0cfc-69c2-4b47-9721-c395647ccb18" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_2f718b6b-9716-4130-a429-0d08e8cc6e7a" xlink:to="loc_srt_RangeAxis_c75b0cfc-69c2-4b47-9721-c395647ccb18" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c75b0cfc-69c2-4b47-9721-c395647ccb18_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_c75b0cfc-69c2-4b47-9721-c395647ccb18" xlink:to="loc_srt_RangeMember_c75b0cfc-69c2-4b47-9721-c395647ccb18_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_615a0594-81ab-4d16-af6f-ea757425927a" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_c75b0cfc-69c2-4b47-9721-c395647ccb18" xlink:to="loc_srt_RangeMember_615a0594-81ab-4d16-af6f-ea757425927a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_3dc961dc-61b2-41e3-950a-b83441817365" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_615a0594-81ab-4d16-af6f-ea757425927a" xlink:to="loc_srt_MinimumMember_3dc961dc-61b2-41e3-950a-b83441817365" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_45a81dac-6306-46a4-bf0c-01ff7f2b244a" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_615a0594-81ab-4d16-af6f-ea757425927a" xlink:to="loc_srt_MaximumMember_45a81dac-6306-46a4-bf0c-01ff7f2b244a" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/USWMAcquisitionProFormaInformationDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#USWMAcquisitionProFormaInformationDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/USWMAcquisitionProFormaInformationDetails" xlink:type="extended" id="i307768ae92bc4b9ba680e04a6998b915_USWMAcquisitionProFormaInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_0ea87e70-2bab-4bc1-a253-3ace6af6c8bd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_c8f23d4b-b144-4acd-ac05-f9fd56c508fa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0ea87e70-2bab-4bc1-a253-3ace6af6c8bd" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_c8f23d4b-b144-4acd-ac05-f9fd56c508fa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_72da73f4-7a78-4767-bc1d-9de83b3902be" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0ea87e70-2bab-4bc1-a253-3ace6af6c8bd" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_72da73f4-7a78-4767-bc1d-9de83b3902be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_bb1743cd-6c66-424d-ac25-20be228c0e68" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0ea87e70-2bab-4bc1-a253-3ace6af6c8bd" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_bb1743cd-6c66-424d-ac25-20be228c0e68" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_afa5daf6-c599-40cf-a559-2bdf56f36d72" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_bb1743cd-6c66-424d-ac25-20be228c0e68" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_afa5daf6-c599-40cf-a559-2bdf56f36d72" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_afa5daf6-c599-40cf-a559-2bdf56f36d72_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_afa5daf6-c599-40cf-a559-2bdf56f36d72" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_afa5daf6-c599-40cf-a559-2bdf56f36d72_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_4e171b5c-e95b-4eb3-9dfd-40a14e22ed66" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_afa5daf6-c599-40cf-a559-2bdf56f36d72" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_4e171b5c-e95b-4eb3-9dfd-40a14e22ed66" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_97897828-2bf0-4feb-b009-5e1e3d684538" xlink:href="supn-20210630.xsd#supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_4e171b5c-e95b-4eb3-9dfd-40a14e22ed66" xlink:to="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_97897828-2bf0-4feb-b009-5e1e3d684538" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/DisaggregatedRevenuesSummaryofRevenuesDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#DisaggregatedRevenuesSummaryofRevenuesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/DisaggregatedRevenuesSummaryofRevenuesDetails" xlink:type="extended" id="i62e52ff2dfb948b49aa89ba6d13effc3_DisaggregatedRevenuesSummaryofRevenuesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_4dd0e744-dec9-461f-852d-9fbdf2008f00" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_53ec63c3-9798-4531-9548-9395fe449b45" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_4dd0e744-dec9-461f-852d-9fbdf2008f00" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_53ec63c3-9798-4531-9548-9395fe449b45" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_bf46ccb5-a995-4260-b0ad-a81f8709b3ec" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_4dd0e744-dec9-461f-852d-9fbdf2008f00" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_bf46ccb5-a995-4260-b0ad-a81f8709b3ec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_37cca735-210c-44a2-80f0-6ae4c2fd8d1d" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_bf46ccb5-a995-4260-b0ad-a81f8709b3ec" xlink:to="loc_srt_ProductOrServiceAxis_37cca735-210c-44a2-80f0-6ae4c2fd8d1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_37cca735-210c-44a2-80f0-6ae4c2fd8d1d_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_37cca735-210c-44a2-80f0-6ae4c2fd8d1d" xlink:to="loc_srt_ProductsAndServicesDomain_37cca735-210c-44a2-80f0-6ae4c2fd8d1d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_bbbb8b12-fdf7-4030-9bc0-51a1c9ad3887" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_37cca735-210c-44a2-80f0-6ae4c2fd8d1d" xlink:to="loc_srt_ProductsAndServicesDomain_bbbb8b12-fdf7-4030-9bc0-51a1c9ad3887" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_c080a805-798e-43f3-89af-1bad2c7bd458" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_bbbb8b12-fdf7-4030-9bc0-51a1c9ad3887" xlink:to="loc_us-gaap_ProductMember_c080a805-798e-43f3-89af-1bad2c7bd458" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_TrokendiXrMember_00afabf0-9c35-4569-8be9-c0cabce4f9e7" xlink:href="supn-20210630.xsd#supn_TrokendiXrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_c080a805-798e-43f3-89af-1bad2c7bd458" xlink:to="loc_supn_TrokendiXrMember_00afabf0-9c35-4569-8be9-c0cabce4f9e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_OxtellarXRMember_82a7594e-49dc-4631-9365-92ea500bf080" xlink:href="supn-20210630.xsd#supn_OxtellarXRMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_c080a805-798e-43f3-89af-1bad2c7bd458" xlink:to="loc_supn_OxtellarXRMember_82a7594e-49dc-4631-9365-92ea500bf080" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_APOKYNMember_b92395c7-cfbf-4d10-8054-387d0163f038" xlink:href="supn-20210630.xsd#supn_APOKYNMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_c080a805-798e-43f3-89af-1bad2c7bd458" xlink:to="loc_supn_APOKYNMember_b92395c7-cfbf-4d10-8054-387d0163f038" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_MYOBLOCMember_1cc83883-8746-44c3-b214-9195c9d98fd4" xlink:href="supn-20210630.xsd#supn_MYOBLOCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_c080a805-798e-43f3-89af-1bad2c7bd458" xlink:to="loc_supn_MYOBLOCMember_1cc83883-8746-44c3-b214-9195c9d98fd4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_XADAGOMember_22ec938c-c2ac-40be-9c3e-62bb047cfa54" xlink:href="supn-20210630.xsd#supn_XADAGOMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_c080a805-798e-43f3-89af-1bad2c7bd458" xlink:to="loc_supn_XADAGOMember_22ec938c-c2ac-40be-9c3e-62bb047cfa54" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_QelbreeMember_5265ed1f-542d-4404-b7c8-4252c05a917f" xlink:href="supn-20210630.xsd#supn_QelbreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_c080a805-798e-43f3-89af-1bad2c7bd458" xlink:to="loc_supn_QelbreeMember_5265ed1f-542d-4404-b7c8-4252c05a917f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RoyaltyMember_925b8e20-d6dd-4299-adc2-b83b60781481" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RoyaltyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_bbbb8b12-fdf7-4030-9bc0-51a1c9ad3887" xlink:to="loc_us-gaap_RoyaltyMember_925b8e20-d6dd-4299-adc2-b83b60781481" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/DisaggregatedRevenuesNarrativeDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#DisaggregatedRevenuesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/DisaggregatedRevenuesNarrativeDetails" xlink:type="extended" id="i74b0dbd8d8bd4000bab64108bde97e83_DisaggregatedRevenuesNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_7b720f63-0b49-436c-8394-c0508cfa44a7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_9b1d1534-cce1-42a7-a0f5-ec493ade37ad" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_7b720f63-0b49-436c-8394-c0508cfa44a7" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_9b1d1534-cce1-42a7-a0f5-ec493ade37ad" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_RevenueFromRoyaltyAgreement_34f03a59-c15a-40b0-b213-2d75d2c6a9ce" xlink:href="supn-20210630.xsd#supn_RevenueFromRoyaltyAgreement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_7b720f63-0b49-436c-8394-c0508cfa44a7" xlink:to="loc_supn_RevenueFromRoyaltyAgreement_34f03a59-c15a-40b0-b213-2d75d2c6a9ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_e6f14bab-134f-4b5e-ab5f-e04c8b935f2c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_7b720f63-0b49-436c-8394-c0508cfa44a7" xlink:to="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_e6f14bab-134f-4b5e-ab5f-e04c8b935f2c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_1c7f355f-f460-471c-a6b4-4dcfbb5db24d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_e6f14bab-134f-4b5e-ab5f-e04c8b935f2c" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_1c7f355f-f460-471c-a6b4-4dcfbb5db24d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_1c7f355f-f460-471c-a6b4-4dcfbb5db24d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_1c7f355f-f460-471c-a6b4-4dcfbb5db24d" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_1c7f355f-f460-471c-a6b4-4dcfbb5db24d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_18c31960-561d-4f18-a8f8-6ee5b15a0675" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_1c7f355f-f460-471c-a6b4-4dcfbb5db24d" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_18c31960-561d-4f18-a8f8-6ee5b15a0675" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerMember_2a4d0142-d2f6-42fd-9b3e-3436ad2aa83c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueFromContractWithCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_18c31960-561d-4f18-a8f8-6ee5b15a0675" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerMember_2a4d0142-d2f6-42fd-9b3e-3436ad2aa83c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_c18c7e18-d531-4e12-8570-5b9c33fce807" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_e6f14bab-134f-4b5e-ab5f-e04c8b935f2c" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_c18c7e18-d531-4e12-8570-5b9c33fce807" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_c18c7e18-d531-4e12-8570-5b9c33fce807_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_c18c7e18-d531-4e12-8570-5b9c33fce807" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_c18c7e18-d531-4e12-8570-5b9c33fce807_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_ae9d1c3a-479c-4957-a888-3c495f3212b0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_c18c7e18-d531-4e12-8570-5b9c33fce807" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_ae9d1c3a-479c-4957-a888-3c495f3212b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductConcentrationRiskMember_9953f1a7-3689-4541-ba74-85795e6cccde" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProductConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_ae9d1c3a-479c-4957-a888-3c495f3212b0" xlink:to="loc_us-gaap_ProductConcentrationRiskMember_9953f1a7-3689-4541-ba74-85795e6cccde" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_8fc9d2a5-5c05-4a36-8fc1-e3c911127cf5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_ae9d1c3a-479c-4957-a888-3c495f3212b0" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_8fc9d2a5-5c05-4a36-8fc1-e3c911127cf5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_aa18d443-4d28-4843-97dc-73996eeac7f5" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_e6f14bab-134f-4b5e-ab5f-e04c8b935f2c" xlink:to="loc_srt_MajorCustomersAxis_aa18d443-4d28-4843-97dc-73996eeac7f5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_aa18d443-4d28-4843-97dc-73996eeac7f5_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_aa18d443-4d28-4843-97dc-73996eeac7f5" xlink:to="loc_srt_NameOfMajorCustomerDomain_aa18d443-4d28-4843-97dc-73996eeac7f5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_d12e2dbd-6764-4a9a-9602-e718528e6d07" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_aa18d443-4d28-4843-97dc-73996eeac7f5" xlink:to="loc_srt_NameOfMajorCustomerDomain_d12e2dbd-6764-4a9a-9602-e718528e6d07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_TrokendiXrMember_0e010625-e5c7-4630-a57e-281a08aeb8e7" xlink:href="supn-20210630.xsd#supn_TrokendiXrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_d12e2dbd-6764-4a9a-9602-e718528e6d07" xlink:to="loc_supn_TrokendiXrMember_0e010625-e5c7-4630-a57e-281a08aeb8e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_ThreeMajorCustomersMember_35f9b8cd-bd39-40f9-b286-a2976d775bb8" xlink:href="supn-20210630.xsd#supn_ThreeMajorCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_d12e2dbd-6764-4a9a-9602-e718528e6d07" xlink:to="loc_supn_ThreeMajorCustomersMember_35f9b8cd-bd39-40f9-b286-a2976d775bb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_a0ddf44b-1314-48e3-acb5-da788f020f80" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_e6f14bab-134f-4b5e-ab5f-e04c8b935f2c" xlink:to="loc_srt_ProductOrServiceAxis_a0ddf44b-1314-48e3-acb5-da788f020f80" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_a0ddf44b-1314-48e3-acb5-da788f020f80_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_a0ddf44b-1314-48e3-acb5-da788f020f80" xlink:to="loc_srt_ProductsAndServicesDomain_a0ddf44b-1314-48e3-acb5-da788f020f80_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_0e7720d2-9ac3-4962-af7f-1a756f502718" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_a0ddf44b-1314-48e3-acb5-da788f020f80" xlink:to="loc_srt_ProductsAndServicesDomain_0e7720d2-9ac3-4962-af7f-1a756f502718" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_TrokendiXrMember_fb25e275-f3cb-468f-95c2-de50ed814274" xlink:href="supn-20210630.xsd#supn_TrokendiXrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_0e7720d2-9ac3-4962-af7f-1a756f502718" xlink:to="loc_supn_TrokendiXrMember_fb25e275-f3cb-468f-95c2-de50ed814274" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_ThreeMajorCustomersMember_9a8853c5-be75-419f-b17c-dec8c0f08759" xlink:href="supn-20210630.xsd#supn_ThreeMajorCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_0e7720d2-9ac3-4962-af7f-1a756f502718" xlink:to="loc_supn_ThreeMajorCustomersMember_9a8853c5-be75-419f-b17c-dec8c0f08759" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/InvestmentsNarrativeDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#InvestmentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/InvestmentsNarrativeDetails" xlink:type="extended" id="icc89cb8a176348909ec1b82a7cac97f8_InvestmentsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityLineItems_6f3f5096-2bcc-47e6-8fbf-fb84281a9cb0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableInterestEntityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_VariableInterestEntityAgreementTerminationNoticePeriod_3c4395b7-04be-479e-b9da-9190211b8176" xlink:href="supn-20210630.xsd#supn_VariableInterestEntityAgreementTerminationNoticePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_6f3f5096-2bcc-47e6-8fbf-fb84281a9cb0" xlink:to="loc_supn_VariableInterestEntityAgreementTerminationNoticePeriod_3c4395b7-04be-479e-b9da-9190211b8176" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_CollaborativeArrangementThresholdForDevelopmentCostsPayments_9603a744-c88f-41a8-a5b5-1f85a240cf43" xlink:href="supn-20210630.xsd#supn_CollaborativeArrangementThresholdForDevelopmentCostsPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_6f3f5096-2bcc-47e6-8fbf-fb84281a9cb0" xlink:to="loc_supn_CollaborativeArrangementThresholdForDevelopmentCostsPayments_9603a744-c88f-41a8-a5b5-1f85a240cf43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_CollaborativeArrangementPaymentForOptionIssueFee_5ab40fa8-c7fc-4dc5-af80-bc0f3ed6f14e" xlink:href="supn-20210630.xsd#supn_CollaborativeArrangementPaymentForOptionIssueFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_6f3f5096-2bcc-47e6-8fbf-fb84281a9cb0" xlink:to="loc_supn_CollaborativeArrangementPaymentForOptionIssueFee_5ab40fa8-c7fc-4dc5-af80-bc0f3ed6f14e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityOwnershipPercentage_902f4cc3-1a91-469f-a1e5-272aa787e100" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableInterestEntityOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_6f3f5096-2bcc-47e6-8fbf-fb84281a9cb0" xlink:to="loc_us-gaap_VariableInterestEntityOwnershipPercentage_902f4cc3-1a91-469f-a1e5-272aa787e100" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded_7eecd3ba-2852-4bd2-a4e0-8d718290ca2d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_6f3f5096-2bcc-47e6-8fbf-fb84281a9cb0" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded_7eecd3ba-2852-4bd2-a4e0-8d718290ca2d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_6c4fcb50-c40d-4b85-832e-9eff4378e088" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfVariableInterestEntitiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_VariableInterestEntityLineItems_6f3f5096-2bcc-47e6-8fbf-fb84281a9cb0" xlink:to="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_6c4fcb50-c40d-4b85-832e-9eff4378e088" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_41d0b7d1-918d-44cc-9a5d-bf77d34480ed" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_6c4fcb50-c40d-4b85-832e-9eff4378e088" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_41d0b7d1-918d-44cc-9a5d-bf77d34480ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_41d0b7d1-918d-44cc-9a5d-bf77d34480ed_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_41d0b7d1-918d-44cc-9a5d-bf77d34480ed" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_41d0b7d1-918d-44cc-9a5d-bf77d34480ed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_9249a618-538b-4f2d-a292-99f656915233" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_41d0b7d1-918d-44cc-9a5d-bf77d34480ed" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_9249a618-538b-4f2d-a292-99f656915233" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_NavitorPharmaceuticalsIncMember_65ab4071-e422-4128-b22e-889eba16ce33" xlink:href="supn-20210630.xsd#supn_NavitorPharmaceuticalsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_9249a618-538b-4f2d-a292-99f656915233" xlink:to="loc_supn_NavitorPharmaceuticalsIncMember_65ab4071-e422-4128-b22e-889eba16ce33" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_31730e0b-41d8-4802-b1d3-a62607d71dea" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfVariableInterestEntitiesTable_6c4fcb50-c40d-4b85-832e-9eff4378e088" xlink:to="loc_srt_ConsolidatedEntitiesAxis_31730e0b-41d8-4802-b1d3-a62607d71dea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_31730e0b-41d8-4802-b1d3-a62607d71dea_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_31730e0b-41d8-4802-b1d3-a62607d71dea" xlink:to="loc_srt_ConsolidatedEntitiesDomain_31730e0b-41d8-4802-b1d3-a62607d71dea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_3e056ec1-7d1a-4767-808a-24296b0c20ef" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_31730e0b-41d8-4802-b1d3-a62607d71dea" xlink:to="loc_srt_ConsolidatedEntitiesDomain_3e056ec1-7d1a-4767-808a-24296b0c20ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_179817f0-54a3-419d-a6af-59f1175b6252" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_3e056ec1-7d1a-4767-808a-24296b0c20ef" xlink:to="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_179817f0-54a3-419d-a6af-59f1175b6252" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/FairValueofFinancialInstrumentsandContingentConsiderationNarrativeDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#FairValueofFinancialInstrumentsandContingentConsiderationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/FairValueofFinancialInstrumentsandContingentConsiderationNarrativeDetails" xlink:type="extended" id="i2f4e1890d41f4a529f06ba65db97cb34_FairValueofFinancialInstrumentsandContingentConsiderationNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_714cf0ec-fb9f-4041-ac53-48c9781be877" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_dea15f05-11a6-416b-a52b-e7a6a5eb0bae" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_714cf0ec-fb9f-4041-ac53-48c9781be877" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_dea15f05-11a6-416b-a52b-e7a6a5eb0bae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded_2c31e43a-a2ac-4067-b34b-b01b1bd436b8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_714cf0ec-fb9f-4041-ac53-48c9781be877" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded_2c31e43a-a2ac-4067-b34b-b01b1bd436b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_b2953959-b46a-456f-acd5-9421856a20eb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_714cf0ec-fb9f-4041-ac53-48c9781be877" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_b2953959-b46a-456f-acd5-9421856a20eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2bb51174-6227-4323-b4fa-131489b79405" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_714cf0ec-fb9f-4041-ac53-48c9781be877" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2bb51174-6227-4323-b4fa-131489b79405" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_f27cf4a8-4b25-49a8-9729-338de5c622ae" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2bb51174-6227-4323-b4fa-131489b79405" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_f27cf4a8-4b25-49a8-9729-338de5c622ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_f27cf4a8-4b25-49a8-9729-338de5c622ae_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_f27cf4a8-4b25-49a8-9729-338de5c622ae" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_f27cf4a8-4b25-49a8-9729-338de5c622ae_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_bbe494a8-16b8-414b-9629-5c90b3b93917" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_f27cf4a8-4b25-49a8-9729-338de5c622ae" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_bbe494a8-16b8-414b-9629-5c90b3b93917" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_3d0ea425-b9d3-4936-956f-2f6dce48111f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_bbe494a8-16b8-414b-9629-5c90b3b93917" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_3d0ea425-b9d3-4936-956f-2f6dce48111f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_31fb97a0-b0ed-445e-980d-ed4a9ee6bc02" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2bb51174-6227-4323-b4fa-131489b79405" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_31fb97a0-b0ed-445e-980d-ed4a9ee6bc02" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_31fb97a0-b0ed-445e-980d-ed4a9ee6bc02_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_31fb97a0-b0ed-445e-980d-ed4a9ee6bc02" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_31fb97a0-b0ed-445e-980d-ed4a9ee6bc02_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f84eab95-dc3e-490f-9dc7-b78e8f664adf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_31fb97a0-b0ed-445e-980d-ed4a9ee6bc02" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f84eab95-dc3e-490f-9dc7-b78e8f664adf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_387d4773-d0ef-481b-8549-3f7245fc7c04" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_f84eab95-dc3e-490f-9dc7-b78e8f664adf" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_387d4773-d0ef-481b-8549-3f7245fc7c04" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesAxis_1baa8d7e-d0e6-4766-8bb8-4d72bd3911ed" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ConsolidatedEntitiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2bb51174-6227-4323-b4fa-131489b79405" xlink:to="loc_srt_ConsolidatedEntitiesAxis_1baa8d7e-d0e6-4766-8bb8-4d72bd3911ed" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_1baa8d7e-d0e6-4766-8bb8-4d72bd3911ed_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidatedEntitiesAxis_1baa8d7e-d0e6-4766-8bb8-4d72bd3911ed" xlink:to="loc_srt_ConsolidatedEntitiesDomain_1baa8d7e-d0e6-4766-8bb8-4d72bd3911ed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidatedEntitiesDomain_17d7659e-8c29-462d-97a7-08c0a4d1b654" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ConsolidatedEntitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidatedEntitiesAxis_1baa8d7e-d0e6-4766-8bb8-4d72bd3911ed" xlink:to="loc_srt_ConsolidatedEntitiesDomain_17d7659e-8c29-462d-97a7-08c0a4d1b654" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_26de0aca-ad92-4f6c-bb2e-a1ae0edc8b13" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidatedEntitiesDomain_17d7659e-8c29-462d-97a7-08c0a4d1b654" xlink:to="loc_us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember_26de0aca-ad92-4f6c-bb2e-a1ae0edc8b13" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_39a145e5-be56-4d6c-be95-5154f0fe14d9" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2bb51174-6227-4323-b4fa-131489b79405" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_39a145e5-be56-4d6c-be95-5154f0fe14d9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_39a145e5-be56-4d6c-be95-5154f0fe14d9_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_39a145e5-be56-4d6c-be95-5154f0fe14d9" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_39a145e5-be56-4d6c-be95-5154f0fe14d9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_5b613d6e-f9b4-4ae3-b9d4-afb066001b57" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_39a145e5-be56-4d6c-be95-5154f0fe14d9" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_5b613d6e-f9b4-4ae3-b9d4-afb066001b57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_NavitorPharmaceuticalsIncMember_7b531391-8880-47f8-a8b8-2af0b17f916b" xlink:href="supn-20210630.xsd#supn_NavitorPharmaceuticalsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_5b613d6e-f9b4-4ae3-b9d4-afb066001b57" xlink:to="loc_supn_NavitorPharmaceuticalsIncMember_7b531391-8880-47f8-a8b8-2af0b17f916b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_37d3c299-eb66-4f85-81c4-5717a6a2ec9d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2bb51174-6227-4323-b4fa-131489b79405" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_37d3c299-eb66-4f85-81c4-5717a6a2ec9d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_37d3c299-eb66-4f85-81c4-5717a6a2ec9d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_37d3c299-eb66-4f85-81c4-5717a6a2ec9d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_37d3c299-eb66-4f85-81c4-5717a6a2ec9d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0ed7c560-135a-41f7-af24-1d798ed6d6df" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_37d3c299-eb66-4f85-81c4-5717a6a2ec9d" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0ed7c560-135a-41f7-af24-1d798ed6d6df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_9682e79a-c23e-4614-aa43-04efb533efbd" xlink:href="supn-20210630.xsd#supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_0ed7c560-135a-41f7-af24-1d798ed6d6df" xlink:to="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_9682e79a-c23e-4614-aa43-04efb533efbd" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/FairValueofFinancialInstrumentsandContingentConsiderationCarryingValueDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#FairValueofFinancialInstrumentsandContingentConsiderationCarryingValueDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/FairValueofFinancialInstrumentsandContingentConsiderationCarryingValueDetails" xlink:type="extended" id="i40be0b77249943caad6088fc76426ddd_FairValueofFinancialInstrumentsandContingentConsiderationCarryingValueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_be68b72e-a312-4bd8-806f-b4d7c50710fd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_5261e365-db30-46d4-857d-dc020c1d7d99" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_be68b72e-a312-4bd8-806f-b4d7c50710fd" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_5261e365-db30-46d4-857d-dc020c1d7d99" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_39b41e7e-882c-4986-a718-4b96246eb0e9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_5261e365-db30-46d4-857d-dc020c1d7d99" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_39b41e7e-882c-4986-a718-4b96246eb0e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesCurrentAbstract_36be67d1-cba4-4b55-8714-307d3a56ebf9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_5261e365-db30-46d4-857d-dc020c1d7d99" xlink:to="loc_us-gaap_DebtSecuritiesCurrentAbstract_36be67d1-cba4-4b55-8714-307d3a56ebf9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_a2c93843-e7a1-4a5c-b57b-8b2cddc15d73" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesCurrentAbstract_36be67d1-cba4-4b55-8714-307d3a56ebf9" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_a2c93843-e7a1-4a5c-b57b-8b2cddc15d73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesNoncurrentAbstract_a3c2fcd0-eee0-4121-9420-a1e45fc08c28" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtSecuritiesNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_5261e365-db30-46d4-857d-dc020c1d7d99" xlink:to="loc_us-gaap_DebtSecuritiesNoncurrentAbstract_a3c2fcd0-eee0-4121-9420-a1e45fc08c28" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent_edc22953-f6a6-4ed8-a711-731392508390" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesNoncurrentAbstract_a3c2fcd0-eee0-4121-9420-a1e45fc08c28" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent_edc22953-f6a6-4ed8-a711-731392508390" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrentAbstract_0ef3e79b-78e9-4571-a8ee-636879eea597" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherAssetsNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_5261e365-db30-46d4-857d-dc020c1d7d99" xlink:to="loc_us-gaap_OtherAssetsNoncurrentAbstract_0ef3e79b-78e9-4571-a8ee-636879eea597" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent_22098753-3726-4b12-9a2a-bb5d625d73fc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherAssetsNoncurrentAbstract_0ef3e79b-78e9-4571-a8ee-636879eea597" xlink:to="loc_us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent_22098753-3726-4b12-9a2a-bb5d625d73fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_5ed1c824-fd41-4f30-b43d-2d27826ef451" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_5261e365-db30-46d4-857d-dc020c1d7d99" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_5ed1c824-fd41-4f30-b43d-2d27826ef451" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_aad1a419-e52c-475b-938d-57fffab67d14" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_be68b72e-a312-4bd8-806f-b4d7c50710fd" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_aad1a419-e52c-475b-938d-57fffab67d14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_a976546b-a6d9-4f27-8e9a-19303cb51acc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_aad1a419-e52c-475b-938d-57fffab67d14" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_a976546b-a6d9-4f27-8e9a-19303cb51acc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesFairValueDisclosure_668f6613-b6d6-419b-b2c3-ad06f4b51825" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesFairValueDisclosureAbstract_aad1a419-e52c-475b-938d-57fffab67d14" xlink:to="loc_us-gaap_LiabilitiesFairValueDisclosure_668f6613-b6d6-419b-b2c3-ad06f4b51825" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_4e62271a-280b-4a9b-b976-15bd7ff5353e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_be68b72e-a312-4bd8-806f-b4d7c50710fd" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_4e62271a-280b-4a9b-b976-15bd7ff5353e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_718779cf-a90e-4392-976d-7d746ee27049" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_4e62271a-280b-4a9b-b976-15bd7ff5353e" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_718779cf-a90e-4392-976d-7d746ee27049" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_718779cf-a90e-4392-976d-7d746ee27049_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_718779cf-a90e-4392-976d-7d746ee27049" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_718779cf-a90e-4392-976d-7d746ee27049_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_8c66882c-36ab-41da-b534-ac0c22187b36" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_718779cf-a90e-4392-976d-7d746ee27049" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_8c66882c-36ab-41da-b534-ac0c22187b36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_f4d2e2ba-18c3-4aa4-bbe8-e2c46a303952" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_8c66882c-36ab-41da-b534-ac0c22187b36" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_f4d2e2ba-18c3-4aa4-bbe8-e2c46a303952" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4d3cdea2-fe48-46b9-8f4e-1b04e163b380" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_4e62271a-280b-4a9b-b976-15bd7ff5353e" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4d3cdea2-fe48-46b9-8f4e-1b04e163b380" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4d3cdea2-fe48-46b9-8f4e-1b04e163b380_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4d3cdea2-fe48-46b9-8f4e-1b04e163b380" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4d3cdea2-fe48-46b9-8f4e-1b04e163b380_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d99b0126-0225-4271-8209-4ac131f49072" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4d3cdea2-fe48-46b9-8f4e-1b04e163b380" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d99b0126-0225-4271-8209-4ac131f49072" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_e8ca2f33-01e6-4836-bfb6-58446029ed07" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d99b0126-0225-4271-8209-4ac131f49072" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_e8ca2f33-01e6-4836-bfb6-58446029ed07" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_f3f49f7d-6c40-4c3f-b255-09a4805c3cff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d99b0126-0225-4271-8209-4ac131f49072" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_f3f49f7d-6c40-4c3f-b255-09a4805c3cff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_fb325750-09b2-44e5-ad89-31c1803027be" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d99b0126-0225-4271-8209-4ac131f49072" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_fb325750-09b2-44e5-ad89-31c1803027be" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_c2af581a-5126-4bff-88ed-23cdb5993f1a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_4e62271a-280b-4a9b-b976-15bd7ff5353e" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_c2af581a-5126-4bff-88ed-23cdb5993f1a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_c2af581a-5126-4bff-88ed-23cdb5993f1a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_c2af581a-5126-4bff-88ed-23cdb5993f1a" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_c2af581a-5126-4bff-88ed-23cdb5993f1a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_c7e2eb96-0f30-40c2-b33a-2266f6238f93" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_c2af581a-5126-4bff-88ed-23cdb5993f1a" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_c7e2eb96-0f30-40c2-b33a-2266f6238f93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashMember_208e406f-f5b5-4f78-b159-d6165d7c62dc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_c7e2eb96-0f30-40c2-b33a-2266f6238f93" xlink:to="loc_us-gaap_CashMember_208e406f-f5b5-4f78-b159-d6165d7c62dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_1f77e668-b07f-42af-9fba-0784b13dcf50" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_c7e2eb96-0f30-40c2-b33a-2266f6238f93" xlink:to="loc_us-gaap_MoneyMarketFundsMember_1f77e668-b07f-42af-9fba-0784b13dcf50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_2181be90-5002-43e4-a76e-f5b227c03c91" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_4e62271a-280b-4a9b-b976-15bd7ff5353e" xlink:to="loc_us-gaap_FinancialInstrumentAxis_2181be90-5002-43e4-a76e-f5b227c03c91" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2181be90-5002-43e4-a76e-f5b227c03c91_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_2181be90-5002-43e4-a76e-f5b227c03c91" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_2181be90-5002-43e4-a76e-f5b227c03c91_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_41ca2ea0-1169-4002-b0b9-b1c839d958cb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_2181be90-5002-43e4-a76e-f5b227c03c91" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_41ca2ea0-1169-4002-b0b9-b1c839d958cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_27d5cfff-d1cf-4982-9e6b-59dcaa55a1e6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_41ca2ea0-1169-4002-b0b9-b1c839d958cb" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_27d5cfff-d1cf-4982-9e6b-59dcaa55a1e6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MunicipalBondsMember_f06e470e-4af4-4ebb-8f00-91050e1ae66b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MunicipalBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_41ca2ea0-1169-4002-b0b9-b1c839d958cb" xlink:to="loc_us-gaap_MunicipalBondsMember_f06e470e-4af4-4ebb-8f00-91050e1ae66b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_75b6c047-3709-414f-9681-61a10beaad5e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_4e62271a-280b-4a9b-b976-15bd7ff5353e" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_75b6c047-3709-414f-9681-61a10beaad5e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_75b6c047-3709-414f-9681-61a10beaad5e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_75b6c047-3709-414f-9681-61a10beaad5e" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_75b6c047-3709-414f-9681-61a10beaad5e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_ada6ca05-39f5-4064-9ee1-a4d499b11dc1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_75b6c047-3709-414f-9681-61a10beaad5e" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_ada6ca05-39f5-4064-9ee1-a4d499b11dc1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_7dd8febe-5ce0-4e6a-885c-f18af27fdeea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_ada6ca05-39f5-4064-9ee1-a4d499b11dc1" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_7dd8febe-5ce0-4e6a-885c-f18af27fdeea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_67fc74f0-53fd-49e4-be54-e2485881d38c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_ada6ca05-39f5-4064-9ee1-a4d499b11dc1" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_67fc74f0-53fd-49e4-be54-e2485881d38c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/FairValueofFinancialInstrumentsandContingentConsiderationReconciliationoftheBeginningandEndingBalancesRelatedtotheContingentConsiderationDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#FairValueofFinancialInstrumentsandContingentConsiderationReconciliationoftheBeginningandEndingBalancesRelatedtotheContingentConsiderationDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/FairValueofFinancialInstrumentsandContingentConsiderationReconciliationoftheBeginningandEndingBalancesRelatedtotheContingentConsiderationDetails" xlink:type="extended" id="i7ed1d6a413194d748d189a9e35874ee5_FairValueofFinancialInstrumentsandContingentConsiderationReconciliationoftheBeginningandEndingBalancesRelatedtotheContingentConsiderationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_bcf527da-8e6d-4c89-998f-00f80854d829" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_cf4f65f5-9e78-4e18-9a6c-69b6bddc2d52" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_bcf527da-8e6d-4c89-998f-00f80854d829" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_cf4f65f5-9e78-4e18-9a6c-69b6bddc2d52" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_8bbe5157-275f-45d3-b07f-0a3f6f74189e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_bcf527da-8e6d-4c89-998f-00f80854d829" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_8bbe5157-275f-45d3-b07f-0a3f6f74189e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationByTypeAxis_49e663ce-9ad6-4753-80e3-1f04b1c39bfe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContingentConsiderationByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_8bbe5157-275f-45d3-b07f-0a3f6f74189e" xlink:to="loc_us-gaap_ContingentConsiderationByTypeAxis_49e663ce-9ad6-4753-80e3-1f04b1c39bfe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_49e663ce-9ad6-4753-80e3-1f04b1c39bfe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_49e663ce-9ad6-4753-80e3-1f04b1c39bfe" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_49e663ce-9ad6-4753-80e3-1f04b1c39bfe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_4e6fc6d2-e9fb-40f7-b8f4-def9189e948d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_49e663ce-9ad6-4753-80e3-1f04b1c39bfe" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_4e6fc6d2-e9fb-40f7-b8f4-def9189e948d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_RegulatoryAndDevelopmentalContingentConsiderationLiabilityMember_7412cb2c-8347-4a6d-ab37-671d6ddb3a8a" xlink:href="supn-20210630.xsd#supn_RegulatoryAndDevelopmentalContingentConsiderationLiabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_4e6fc6d2-e9fb-40f7-b8f4-def9189e948d" xlink:to="loc_supn_RegulatoryAndDevelopmentalContingentConsiderationLiabilityMember_7412cb2c-8347-4a6d-ab37-671d6ddb3a8a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_SalesBasedContingentConsiderationLiabilityMember_8845bddf-dde8-4cd4-b1c6-3a32a9de2809" xlink:href="supn-20210630.xsd#supn_SalesBasedContingentConsiderationLiabilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_4e6fc6d2-e9fb-40f7-b8f4-def9189e948d" xlink:to="loc_supn_SalesBasedContingentConsiderationLiabilityMember_8845bddf-dde8-4cd4-b1c6-3a32a9de2809" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/GoodwillandIntangibleAssetsNetGoodwillandIntangibleAssetsGrossCarryingAmountandRelatedAccumulatedAmortizationDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#GoodwillandIntangibleAssetsNetGoodwillandIntangibleAssetsGrossCarryingAmountandRelatedAccumulatedAmortizationDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/GoodwillandIntangibleAssetsNetGoodwillandIntangibleAssetsGrossCarryingAmountandRelatedAccumulatedAmortizationDetails" xlink:type="extended" id="i2a008f840ce74e4bae222c23de842be0_GoodwillandIntangibleAssetsNetGoodwillandIntangibleAssetsGrossCarryingAmountandRelatedAccumulatedAmortizationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_c19f6f67-fb58-4ebf-8704-0651094d9197" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_9973b787-7334-4554-8d78-6c48b7cf9c08" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_c19f6f67-fb58-4ebf-8704-0651094d9197" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_9973b787-7334-4554-8d78-6c48b7cf9c08" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_46f14a0d-ec12-4499-8e2a-4fb3d718390b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_c19f6f67-fb58-4ebf-8704-0651094d9197" xlink:to="loc_us-gaap_Goodwill_46f14a0d-ec12-4499-8e2a-4fb3d718390b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_e7f8e329-24a2-4eab-aeb1-d8a3afa51580" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_c19f6f67-fb58-4ebf-8704-0651094d9197" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_e7f8e329-24a2-4eab-aeb1-d8a3afa51580" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_6b2ef9c6-510c-450d-81e4-9f62c79be676" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_c19f6f67-fb58-4ebf-8704-0651094d9197" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_6b2ef9c6-510c-450d-81e4-9f62c79be676" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_cd033d92-1016-4cd2-94c0-2232c673f69f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_c19f6f67-fb58-4ebf-8704-0651094d9197" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_cd033d92-1016-4cd2-94c0-2232c673f69f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_b98db06c-b3c2-4f78-8451-de27fb111d5f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_c19f6f67-fb58-4ebf-8704-0651094d9197" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_b98db06c-b3c2-4f78-8451-de27fb111d5f" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_373f9d5e-3961-47c8-9183-960688ec7510" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_c19f6f67-fb58-4ebf-8704-0651094d9197" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_373f9d5e-3961-47c8-9183-960688ec7510" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_a53a847b-8dec-4717-a758-25fe26d11b70" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_373f9d5e-3961-47c8-9183-960688ec7510" xlink:to="loc_srt_RangeAxis_a53a847b-8dec-4717-a758-25fe26d11b70" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_a53a847b-8dec-4717-a758-25fe26d11b70_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_a53a847b-8dec-4717-a758-25fe26d11b70" xlink:to="loc_srt_RangeMember_a53a847b-8dec-4717-a758-25fe26d11b70_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_25948dac-fb88-4e8d-8fa8-49114b5da0b0" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_a53a847b-8dec-4717-a758-25fe26d11b70" xlink:to="loc_srt_RangeMember_25948dac-fb88-4e8d-8fa8-49114b5da0b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_c40a1317-4ebe-4205-9793-8f00e36c8e10" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_25948dac-fb88-4e8d-8fa8-49114b5da0b0" xlink:to="loc_srt_MinimumMember_c40a1317-4ebe-4205-9793-8f00e36c8e10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_78252441-b5c0-4e87-9a7c-49e0b7c2c235" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_25948dac-fb88-4e8d-8fa8-49114b5da0b0" xlink:to="loc_srt_MaximumMember_78252441-b5c0-4e87-9a7c-49e0b7c2c235" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_66126ff7-3e22-4ef8-8a0d-747ce2bdc4e2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_373f9d5e-3961-47c8-9183-960688ec7510" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_66126ff7-3e22-4ef8-8a0d-747ce2bdc4e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_66126ff7-3e22-4ef8-8a0d-747ce2bdc4e2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_66126ff7-3e22-4ef8-8a0d-747ce2bdc4e2" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_66126ff7-3e22-4ef8-8a0d-747ce2bdc4e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_a13e0899-a8c6-4a2b-83cf-8c2c98f55ca8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_66126ff7-3e22-4ef8-8a0d-747ce2bdc4e2" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_a13e0899-a8c6-4a2b-83cf-8c2c98f55ca8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InProcessResearchAndDevelopmentMember_a0287cf6-d24b-481c-b38f-2a0305b9c405" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InProcessResearchAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_a13e0899-a8c6-4a2b-83cf-8c2c98f55ca8" xlink:to="loc_us-gaap_InProcessResearchAndDevelopmentMember_a0287cf6-d24b-481c-b38f-2a0305b9c405" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_73e028cf-fb26-49d6-ac6a-d06f9b23d98a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_373f9d5e-3961-47c8-9183-960688ec7510" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_73e028cf-fb26-49d6-ac6a-d06f9b23d98a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_73e028cf-fb26-49d6-ac6a-d06f9b23d98a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_73e028cf-fb26-49d6-ac6a-d06f9b23d98a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_73e028cf-fb26-49d6-ac6a-d06f9b23d98a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_d505b6a3-e580-4a07-852f-75ec5f2e4761" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_73e028cf-fb26-49d6-ac6a-d06f9b23d98a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_d505b6a3-e580-4a07-852f-75ec5f2e4761" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_eb5fc8d4-9f4e-46bc-8518-5189b6f3f731" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_d505b6a3-e580-4a07-852f-75ec5f2e4761" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_eb5fc8d4-9f4e-46bc-8518-5189b6f3f731" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_PatentDefenseCostsMember_890dc7e9-9d7b-41ab-98d1-90ec5f7c5f73" xlink:href="supn-20210630.xsd#supn_PatentDefenseCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_d505b6a3-e580-4a07-852f-75ec5f2e4761" xlink:to="loc_supn_PatentDefenseCostsMember_890dc7e9-9d7b-41ab-98d1-90ec5f7c5f73" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/ConvertibleSeniorNotesDue2023NarrativeDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#ConvertibleSeniorNotesDue2023NarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ConvertibleSeniorNotesDue2023NarrativeDetails" xlink:type="extended" id="ic7befe64656b4d6e9b01edd92cbd3932_ConvertibleSeniorNotesDue2023NarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_9e44540c-674a-4ef6-b42d-8c5197fefea1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_9e44540c-674a-4ef6-b42d-8c5197fefea1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_b4899b19-b401-480a-a9e8-cf1f3797a8d8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_b4899b19-b401-480a-a9e8-cf1f3797a8d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_ec13865e-2302-4a42-8a91-4479c052f466" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_ec13865e-2302-4a42-8a91-4479c052f466" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_ac4726fa-2dbb-47f8-83c1-1bb39bb60b70" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_ac4726fa-2dbb-47f8-83c1-1bb39bb60b70" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_be1d843b-ba2e-49ca-b311-bb11b285b1e6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_be1d843b-ba2e-49ca-b311-bb11b285b1e6" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleStockPriceTrigger_bcb358fa-7a2f-4cd4-91c2-a5c82dbd0a00" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentConvertibleStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_us-gaap_DebtInstrumentConvertibleStockPriceTrigger_bcb358fa-7a2f-4cd4-91c2-a5c82dbd0a00" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_e2c7ae52-4243-41ed-b5b1-2cabefc0e49c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_e2c7ae52-4243-41ed-b5b1-2cabefc0e49c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_3be4b8b3-efcf-4674-bd5c-e9ae47774ad1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_3be4b8b3-efcf-4674-bd5c-e9ae47774ad1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1_86ea28aa-6f4c-42be-a19c-db709ca2da3b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1_86ea28aa-6f4c-42be-a19c-db709ca2da3b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionConvertedInstrumentSharesIssued1_36c1d2de-efef-4edf-8577-8a7cdc091a4f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtConversionConvertedInstrumentSharesIssued1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_us-gaap_DebtConversionConvertedInstrumentSharesIssued1_36c1d2de-efef-4edf-8577-8a7cdc091a4f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_4a45c632-5b85-4450-b390-0437b8635a2f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_4a45c632-5b85-4450-b390-0437b8635a2f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_ClassOfWarrantOrRightNumberOfSharesInWhichHolderCanBeEntitledPerWarrantsAtStrikePrice_77c4fc68-2503-4b58-80dd-69377284e9d3" xlink:href="supn-20210630.xsd#supn_ClassOfWarrantOrRightNumberOfSharesInWhichHolderCanBeEntitledPerWarrantsAtStrikePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_supn_ClassOfWarrantOrRightNumberOfSharesInWhichHolderCanBeEntitledPerWarrantsAtStrikePrice_77c4fc68-2503-4b58-80dd-69377284e9d3" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_13f8cfce-d37a-4300-b863-0aa42b33e342" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_13f8cfce-d37a-4300-b863-0aa42b33e342" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionOriginalDebtAmount1_a887394d-1304-416b-9dfa-6814547fc057" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtConversionOriginalDebtAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_us-gaap_DebtConversionOriginalDebtAmount1_a887394d-1304-416b-9dfa-6814547fc057" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_d6260f99-3896-4f5e-bde9-1535426c1cd7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01207843-b8ec-4d8e-823b-e105b27be0c2" xlink:to="loc_us-gaap_DebtInstrumentTable_d6260f99-3896-4f5e-bde9-1535426c1cd7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_8df2a738-4780-4855-8d16-88795cab9588" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_d6260f99-3896-4f5e-bde9-1535426c1cd7" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_8df2a738-4780-4855-8d16-88795cab9588" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_8df2a738-4780-4855-8d16-88795cab9588_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_8df2a738-4780-4855-8d16-88795cab9588" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_8df2a738-4780-4855-8d16-88795cab9588_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_f4becfdd-95cf-422c-b607-ecc585d4d8d4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_8df2a738-4780-4855-8d16-88795cab9588" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_f4becfdd-95cf-422c-b607-ecc585d4d8d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_104b420b-b4e4-4ee7-af18-edfff324435b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_f4becfdd-95cf-422c-b607-ecc585d4d8d4" xlink:to="loc_us-gaap_ConvertibleDebtMember_104b420b-b4e4-4ee7-af18-edfff324435b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionByUniqueDescriptionAxis_49db8b78-442d-4179-b766-fe586e8b7f86" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtConversionByUniqueDescriptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_d6260f99-3896-4f5e-bde9-1535426c1cd7" xlink:to="loc_us-gaap_DebtConversionByUniqueDescriptionAxis_49db8b78-442d-4179-b766-fe586e8b7f86" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionNameDomain_49db8b78-442d-4179-b766-fe586e8b7f86_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtConversionNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtConversionByUniqueDescriptionAxis_49db8b78-442d-4179-b766-fe586e8b7f86" xlink:to="loc_us-gaap_DebtConversionNameDomain_49db8b78-442d-4179-b766-fe586e8b7f86_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionNameDomain_665cc1b1-6709-44fb-9dc7-69aecc65a6f4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtConversionNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtConversionByUniqueDescriptionAxis_49db8b78-442d-4179-b766-fe586e8b7f86" xlink:to="loc_us-gaap_DebtConversionNameDomain_665cc1b1-6709-44fb-9dc7-69aecc65a6f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_ConversionCircumstanceOneMember_97d852c3-f53a-40b4-9102-12ea213313bb" xlink:href="supn-20210630.xsd#supn_ConversionCircumstanceOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtConversionNameDomain_665cc1b1-6709-44fb-9dc7-69aecc65a6f4" xlink:to="loc_supn_ConversionCircumstanceOneMember_97d852c3-f53a-40b4-9102-12ea213313bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_ConversionCircumstanceTwoMember_275521e1-55a0-4c66-9bb7-fd302e1ec6a8" xlink:href="supn-20210630.xsd#supn_ConversionCircumstanceTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtConversionNameDomain_665cc1b1-6709-44fb-9dc7-69aecc65a6f4" xlink:to="loc_supn_ConversionCircumstanceTwoMember_275521e1-55a0-4c66-9bb7-fd302e1ec6a8" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/ConvertibleSeniorNotesDue2023Summaryofliabilitycomponentof2023NotesDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#ConvertibleSeniorNotesDue2023Summaryofliabilitycomponentof2023NotesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ConvertibleSeniorNotesDue2023Summaryofliabilitycomponentof2023NotesDetails" xlink:type="extended" id="ibf48cb5632a2466cac5b37226e2d22fb_ConvertibleSeniorNotesDue2023Summaryofliabilitycomponentof2023NotesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_d687712c-6798-4bb4-878e-dc32c1f15d8c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_138e0b9e-b158-462f-9d69-1facebe30806" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d687712c-6798-4bb4-878e-dc32c1f15d8c" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_138e0b9e-b158-462f-9d69-1facebe30806" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_ab2c014c-6ccb-4101-ab26-385c19bc56ee" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d687712c-6798-4bb4-878e-dc32c1f15d8c" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_ab2c014c-6ccb-4101-ab26-385c19bc56ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleLongTermNotesPayable_29642a45-e679-4c7e-9c6c-d796fff8cf64" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConvertibleLongTermNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d687712c-6798-4bb4-878e-dc32c1f15d8c" xlink:to="loc_us-gaap_ConvertibleLongTermNotesPayable_29642a45-e679-4c7e-9c6c-d796fff8cf64" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtFairValueDisclosures_cbf5fcf6-507b-4b55-a229-5f6bff162923" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConvertibleDebtFairValueDisclosures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d687712c-6798-4bb4-878e-dc32c1f15d8c" xlink:to="loc_us-gaap_ConvertibleDebtFairValueDisclosures_cbf5fcf6-507b-4b55-a229-5f6bff162923" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_36863a46-ad82-4028-b203-697a3ae69561" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d687712c-6798-4bb4-878e-dc32c1f15d8c" xlink:to="loc_us-gaap_DebtInstrumentTable_36863a46-ad82-4028-b203-697a3ae69561" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_e398ea9c-62c9-469b-8700-aed64a40dfe7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_36863a46-ad82-4028-b203-697a3ae69561" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_e398ea9c-62c9-469b-8700-aed64a40dfe7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_e398ea9c-62c9-469b-8700-aed64a40dfe7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_e398ea9c-62c9-469b-8700-aed64a40dfe7" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_e398ea9c-62c9-469b-8700-aed64a40dfe7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_2f9b9b60-4cf3-4630-8650-87556df4717b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_e398ea9c-62c9-469b-8700-aed64a40dfe7" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_2f9b9b60-4cf3-4630-8650-87556df4717b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_f02bf4db-a181-40cd-b57e-61a6140f6117" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_2f9b9b60-4cf3-4630-8650-87556df4717b" xlink:to="loc_us-gaap_ConvertibleDebtMember_f02bf4db-a181-40cd-b57e-61a6140f6117" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleNotesPayableMember_77982143-b347-427b-92af-642b85534412" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConvertibleNotesPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_2f9b9b60-4cf3-4630-8650-87556df4717b" xlink:to="loc_us-gaap_ConvertibleNotesPayableMember_77982143-b347-427b-92af-642b85534412" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_d1dec358-29f7-45a7-82b2-2224c651b327" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_36863a46-ad82-4028-b203-697a3ae69561" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_d1dec358-29f7-45a7-82b2-2224c651b327" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d1dec358-29f7-45a7-82b2-2224c651b327_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_d1dec358-29f7-45a7-82b2-2224c651b327" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d1dec358-29f7-45a7-82b2-2224c651b327_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_84a8fb13-3662-4475-be31-21f8a4d15e3b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_d1dec358-29f7-45a7-82b2-2224c651b327" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_84a8fb13-3662-4475-be31-21f8a4d15e3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_da2992ef-5051-4f24-b0b3-71f7df671532" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_84a8fb13-3662-4475-be31-21f8a4d15e3b" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_da2992ef-5051-4f24-b0b3-71f7df671532" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/ShareBasedPaymentsSharebasedCompensationExpenseDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#ShareBasedPaymentsSharebasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ShareBasedPaymentsSharebasedCompensationExpenseDetails" xlink:type="extended" id="idcc856e437f246518ad079b03674a097_ShareBasedPaymentsSharebasedCompensationExpenseDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_791b3151-4c67-4a86-8692-6dafa15c64f9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_1117fc76-b4d1-4a84-986e-82664b65352f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_791b3151-4c67-4a86-8692-6dafa15c64f9" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_1117fc76-b4d1-4a84-986e-82664b65352f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_a1647f95-a7a9-40e5-9269-6d31fd7c7488" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_791b3151-4c67-4a86-8692-6dafa15c64f9" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_a1647f95-a7a9-40e5-9269-6d31fd7c7488" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_73fe71be-4c86-43a4-bf66-61ef0770f4a6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_a1647f95-a7a9-40e5-9269-6d31fd7c7488" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_73fe71be-4c86-43a4-bf66-61ef0770f4a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_73fe71be-4c86-43a4-bf66-61ef0770f4a6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_73fe71be-4c86-43a4-bf66-61ef0770f4a6" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_73fe71be-4c86-43a4-bf66-61ef0770f4a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_46498aa5-db5f-4c6a-a305-48939db46938" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_73fe71be-4c86-43a4-bf66-61ef0770f4a6" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_46498aa5-db5f-4c6a-a305-48939db46938" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_4d6217a2-8485-47fe-81c9-e4a7279dec8b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_46498aa5-db5f-4c6a-a305-48939db46938" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_4d6217a2-8485-47fe-81c9-e4a7279dec8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_b65503ba-5607-4c4b-bd85-319d1e767d8c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_46498aa5-db5f-4c6a-a305-48939db46938" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_b65503ba-5607-4c4b-bd85-319d1e767d8c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/ShareBasedPaymentsSARActivityDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#ShareBasedPaymentsSARActivityDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ShareBasedPaymentsSARActivityDetails" xlink:type="extended" id="i99ab4bf51e8f4f8db758e546f5f25418_ShareBasedPaymentsSARActivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6c03c45f-2f9b-43a2-badf-e03a42f168f4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_d58cbd37-bebd-4574-92e2-a5f82b8f7e1d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6c03c45f-2f9b-43a2-badf-e03a42f168f4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_d58cbd37-bebd-4574-92e2-a5f82b8f7e1d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_c4dc55fa-4e8a-4f9b-99ad-0d3d15dba1fb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_d58cbd37-bebd-4574-92e2-a5f82b8f7e1d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_c4dc55fa-4e8a-4f9b-99ad-0d3d15dba1fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_815a179a-5c5c-462b-9b63-f50b407f03a4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_d58cbd37-bebd-4574-92e2-a5f82b8f7e1d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_815a179a-5c5c-462b-9b63-f50b407f03a4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_771dd649-212c-418b-9d3c-adf44674d0c9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_d58cbd37-bebd-4574-92e2-a5f82b8f7e1d" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_771dd649-212c-418b-9d3c-adf44674d0c9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_e02b5bd4-5b98-4183-aa8e-9fddc2cd9330" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_d58cbd37-bebd-4574-92e2-a5f82b8f7e1d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_e02b5bd4-5b98-4183-aa8e-9fddc2cd9330" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_ff1714c5-7548-4e71-a934-8095f47e9bd1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_d70df708-031f-4cd1-b2d8-b6e4891f0967" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6c03c45f-2f9b-43a2-badf-e03a42f168f4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_d70df708-031f-4cd1-b2d8-b6e4891f0967" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_ae522cc9-dcbb-46ce-8eef-98afaf9bd1b2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6c03c45f-2f9b-43a2-badf-e03a42f168f4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_ae522cc9-dcbb-46ce-8eef-98afaf9bd1b2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_52e0d51b-d726-4c23-9d0d-aee6e3b7fb42" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6c03c45f-2f9b-43a2-badf-e03a42f168f4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_52e0d51b-d726-4c23-9d0d-aee6e3b7fb42" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_03b7e34e-3626-41ca-b42f-0f2e0862015f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_52e0d51b-d726-4c23-9d0d-aee6e3b7fb42" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_03b7e34e-3626-41ca-b42f-0f2e0862015f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_12568915-c995-47e4-afe1-eeb0c9f87956" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_52e0d51b-d726-4c23-9d0d-aee6e3b7fb42" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_12568915-c995-47e4-afe1-eeb0c9f87956" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_2fc598aa-310a-4844-89ba-48cd9d1580b0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_52e0d51b-d726-4c23-9d0d-aee6e3b7fb42" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_2fc598aa-310a-4844-89ba-48cd9d1580b0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_d9ebf444-fb1f-443c-ac7f-2e9c2da0c14c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_52e0d51b-d726-4c23-9d0d-aee6e3b7fb42" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_d9ebf444-fb1f-443c-ac7f-2e9c2da0c14c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_e4060bf4-9325-4acf-9b8b-ddaedaca2a77" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_e7143a2d-1025-4365-80cf-534880d826d2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6c03c45f-2f9b-43a2-badf-e03a42f168f4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_e7143a2d-1025-4365-80cf-534880d826d2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_8124dcb9-4335-45d9-8d9f-465ac415d72b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6c03c45f-2f9b-43a2-badf-e03a42f168f4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_8124dcb9-4335-45d9-8d9f-465ac415d72b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_bfb7d6b7-4ddd-4b75-8261-1ef49ccad206" xlink:href="supn-20210630.xsd#supn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6c03c45f-2f9b-43a2-badf-e03a42f168f4" xlink:to="loc_supn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_bfb7d6b7-4ddd-4b75-8261-1ef49ccad206" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_a94e8530-3865-42f0-8b24-8002a151c6fb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_supn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_bfb7d6b7-4ddd-4b75-8261-1ef49ccad206" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_a94e8530-3865-42f0-8b24-8002a151c6fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_05a83382-fae5-41d0-a61f-0a4372e1310c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_supn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_bfb7d6b7-4ddd-4b75-8261-1ef49ccad206" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_05a83382-fae5-41d0-a61f-0a4372e1310c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_61800b1f-4768-4c39-864f-23c56e14c75a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_supn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_bfb7d6b7-4ddd-4b75-8261-1ef49ccad206" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_61800b1f-4768-4c39-864f-23c56e14c75a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1a4fc82c-0ea0-496a-aac0-4054309fa89d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_6c03c45f-2f9b-43a2-badf-e03a42f168f4" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1a4fc82c-0ea0-496a-aac0-4054309fa89d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_972abb5a-db06-4cdf-ab41-7930c0c8cc97" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_1a4fc82c-0ea0-496a-aac0-4054309fa89d" xlink:to="loc_us-gaap_AwardTypeAxis_972abb5a-db06-4cdf-ab41-7930c0c8cc97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_972abb5a-db06-4cdf-ab41-7930c0c8cc97_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_972abb5a-db06-4cdf-ab41-7930c0c8cc97" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_972abb5a-db06-4cdf-ab41-7930c0c8cc97_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_659e35a2-5e53-4f9a-8237-d5d4dd092c88" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_972abb5a-db06-4cdf-ab41-7930c0c8cc97" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_659e35a2-5e53-4f9a-8237-d5d4dd092c88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_StockOptionStockAppreciationRightsMember_62a189ef-2c86-4ff3-9a83-fe56dcf42054" xlink:href="supn-20210630.xsd#supn_StockOptionStockAppreciationRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_659e35a2-5e53-4f9a-8237-d5d4dd092c88" xlink:to="loc_supn_StockOptionStockAppreciationRightsMember_62a189ef-2c86-4ff3-9a83-fe56dcf42054" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/ShareBasedPaymentsRestrictedStockUnitsDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#ShareBasedPaymentsRestrictedStockUnitsDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ShareBasedPaymentsRestrictedStockUnitsDetails" xlink:type="extended" id="if12b4ded4c4b4f01a8b27150a5bd6b9d_ShareBasedPaymentsRestrictedStockUnitsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ca7b4517-3f42-4bba-9ab2-45cc963e5407" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_9e13458d-bf21-4be9-9f0f-94d54cde1a8c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ca7b4517-3f42-4bba-9ab2-45cc963e5407" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_9e13458d-bf21-4be9-9f0f-94d54cde1a8c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_0dc507f9-128a-4633-bc66-e96de4867fd4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_9e13458d-bf21-4be9-9f0f-94d54cde1a8c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_0dc507f9-128a-4633-bc66-e96de4867fd4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_1d2f0740-7652-4fe9-a03e-92d467e06ba9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_9e13458d-bf21-4be9-9f0f-94d54cde1a8c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_1d2f0740-7652-4fe9-a03e-92d467e06ba9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_3f470071-17ed-4eee-a853-029eae2e22d5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_9e13458d-bf21-4be9-9f0f-94d54cde1a8c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_3f470071-17ed-4eee-a853-029eae2e22d5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_6fbfe906-4e9f-4bca-a56d-4ca13eb5b4ca" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_9e13458d-bf21-4be9-9f0f-94d54cde1a8c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_6fbfe906-4e9f-4bca-a56d-4ca13eb5b4ca" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_0883622a-474b-4280-a6ee-cecb4459f14f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_d4191026-5841-4d52-973a-cb71299b8732" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ca7b4517-3f42-4bba-9ab2-45cc963e5407" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_d4191026-5841-4d52-973a-cb71299b8732" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_93b87d38-2352-4139-8881-ab8e0a75ab56" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_d4191026-5841-4d52-973a-cb71299b8732" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_93b87d38-2352-4139-8881-ab8e0a75ab56" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_648ca5f4-e804-41ce-8af4-96e3ae3ce1bd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_d4191026-5841-4d52-973a-cb71299b8732" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_648ca5f4-e804-41ce-8af4-96e3ae3ce1bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_aeba1c05-65db-4f16-91d3-38364ed6092d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_d4191026-5841-4d52-973a-cb71299b8732" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_aeba1c05-65db-4f16-91d3-38364ed6092d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_b541b85d-2081-47d2-9b9b-d8745f943cd1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_d4191026-5841-4d52-973a-cb71299b8732" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_b541b85d-2081-47d2-9b9b-d8745f943cd1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_c2e94940-8da5-48a4-8ca9-954eef48bd79" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_db9293f3-d0a6-4cbe-86e3-58bbd447773c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_ca7b4517-3f42-4bba-9ab2-45cc963e5407" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_db9293f3-d0a6-4cbe-86e3-58bbd447773c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_c125bf65-8c67-4ddc-931c-f9a933781301" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_db9293f3-d0a6-4cbe-86e3-58bbd447773c" xlink:to="loc_us-gaap_AwardTypeAxis_c125bf65-8c67-4ddc-931c-f9a933781301" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c125bf65-8c67-4ddc-931c-f9a933781301_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_c125bf65-8c67-4ddc-931c-f9a933781301" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c125bf65-8c67-4ddc-931c-f9a933781301_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5829c895-fb09-4304-9cb8-ae4b15d66397" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_c125bf65-8c67-4ddc-931c-f9a933781301" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5829c895-fb09-4304-9cb8-ae4b15d66397" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_db7a19d7-27ba-4c94-81d8-ed3e3499ac09" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_5829c895-fb09-4304-9cb8-ae4b15d66397" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_db7a19d7-27ba-4c94-81d8-ed3e3499ac09" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/ShareBasedPaymentsPerformanceStockUnitsDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#ShareBasedPaymentsPerformanceStockUnitsDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ShareBasedPaymentsPerformanceStockUnitsDetails" xlink:type="extended" id="ic709e8e09396458b87d97b2cea297e36_ShareBasedPaymentsPerformanceStockUnitsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1b56eb7f-3440-46e4-843a-c02fccbaf3de" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_11e34935-4074-457e-bc50-f5a3544c8123" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1b56eb7f-3440-46e4-843a-c02fccbaf3de" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_11e34935-4074-457e-bc50-f5a3544c8123" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_6cf2236b-fe68-4572-85e1-3fdab4d0e670" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_11e34935-4074-457e-bc50-f5a3544c8123" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_6cf2236b-fe68-4572-85e1-3fdab4d0e670" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_4a1c80f2-7c8b-4d7d-b45a-587feced35f1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_11e34935-4074-457e-bc50-f5a3544c8123" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_4a1c80f2-7c8b-4d7d-b45a-587feced35f1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_b73a24ae-98c7-4cc6-a078-dbd9e920e308" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_20c766e1-9677-4ac2-b30e-b72fa65c3f7f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1b56eb7f-3440-46e4-843a-c02fccbaf3de" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_20c766e1-9677-4ac2-b30e-b72fa65c3f7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_d93d191c-7a6b-431f-a6d6-4202b8d9dfd7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_20c766e1-9677-4ac2-b30e-b72fa65c3f7f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_d93d191c-7a6b-431f-a6d6-4202b8d9dfd7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_afe480b1-8e23-417d-b685-b14faf62d9d2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_20c766e1-9677-4ac2-b30e-b72fa65c3f7f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_afe480b1-8e23-417d-b685-b14faf62d9d2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_bc625fca-bbad-4b08-b9f4-6437d7d13401" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_6ab623f7-011d-480a-9b20-b606178582f9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1b56eb7f-3440-46e4-843a-c02fccbaf3de" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_6ab623f7-011d-480a-9b20-b606178582f9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_2c572e30-e945-4556-9c96-cb7664bf43a9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1b56eb7f-3440-46e4-843a-c02fccbaf3de" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_2c572e30-e945-4556-9c96-cb7664bf43a9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c1343636-07c2-4715-b509-1d87946fd33e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1b56eb7f-3440-46e4-843a-c02fccbaf3de" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c1343636-07c2-4715-b509-1d87946fd33e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_0d2ef107-a0f4-4894-bacd-453a63212f04" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_c1343636-07c2-4715-b509-1d87946fd33e" xlink:to="loc_us-gaap_AwardTypeAxis_0d2ef107-a0f4-4894-bacd-453a63212f04" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0d2ef107-a0f4-4894-bacd-453a63212f04_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_0d2ef107-a0f4-4894-bacd-453a63212f04" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_0d2ef107-a0f4-4894-bacd-453a63212f04_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6898a830-81ab-49d3-904b-4115f8de7f0a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_0d2ef107-a0f4-4894-bacd-453a63212f04" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6898a830-81ab-49d3-904b-4115f8de7f0a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_d3030c1b-0a2f-40fd-a27d-8f2ef650aeaf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6898a830-81ab-49d3-904b-4115f8de7f0a" xlink:to="loc_us-gaap_PerformanceSharesMember_d3030c1b-0a2f-40fd-a27d-8f2ef650aeaf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_PerformanceBasedUnitsMember_635bbc18-71ba-4cdd-b8e2-c5b2ba1bbfd0" xlink:href="supn-20210630.xsd#supn_PerformanceBasedUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PerformanceSharesMember_d3030c1b-0a2f-40fd-a27d-8f2ef650aeaf" xlink:to="loc_supn_PerformanceBasedUnitsMember_635bbc18-71ba-4cdd-b8e2-c5b2ba1bbfd0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_MarketBasedUnitsMember_282faad0-cede-45f3-8bcc-c1cd7e292033" xlink:href="supn-20210630.xsd#supn_MarketBasedUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PerformanceSharesMember_d3030c1b-0a2f-40fd-a27d-8f2ef650aeaf" xlink:to="loc_supn_MarketBasedUnitsMember_282faad0-cede-45f3-8bcc-c1cd7e292033" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/EarningsperShareDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#EarningsperShareDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/EarningsperShareDetails" xlink:type="extended" id="i8af154019f2b4109b5ec8055408ef057_EarningsperShareDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1f53bd84-5ba9-4439-8e77-3e0c01952b27" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_0a522109-ef53-4c88-9018-71c5f3b9c630" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1f53bd84-5ba9-4439-8e77-3e0c01952b27" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_0a522109-ef53-4c88-9018-71c5f3b9c630" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_d9fdbf36-3ea5-4543-84d1-cdd9f3e52019" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1f53bd84-5ba9-4439-8e77-3e0c01952b27" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_d9fdbf36-3ea5-4543-84d1-cdd9f3e52019" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_af13a762-d065-45e4-8fa7-722075bff137" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1f53bd84-5ba9-4439-8e77-3e0c01952b27" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_af13a762-d065-45e4-8fa7-722075bff137" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_b01340d7-d0f3-41d7-abd8-86d3910b77bf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1f53bd84-5ba9-4439-8e77-3e0c01952b27" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_b01340d7-d0f3-41d7-abd8-86d3910b77bf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_30f2866d-847a-4482-8599-4e9ee4f71e3f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_b01340d7-d0f3-41d7-abd8-86d3910b77bf" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_30f2866d-847a-4482-8599-4e9ee4f71e3f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_a4ece271-fee2-4ab2-926b-ba5ddcfc5623" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1f53bd84-5ba9-4439-8e77-3e0c01952b27" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_a4ece271-fee2-4ab2-926b-ba5ddcfc5623" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_c3843916-8a6e-4026-99f5-91dd7cf29c44" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_a4ece271-fee2-4ab2-926b-ba5ddcfc5623" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_c3843916-8a6e-4026-99f5-91dd7cf29c44" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_22ad8ee4-daab-4352-a719-ac9632535b88" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1f53bd84-5ba9-4439-8e77-3e0c01952b27" xlink:to="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_22ad8ee4-daab-4352-a719-ac9632535b88" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_66e3d529-abbf-4555-b179-495369193ebd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_22ad8ee4-daab-4352-a719-ac9632535b88" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_66e3d529-abbf-4555-b179-495369193ebd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_ae762309-5276-43c4-b127-2e205800f747" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1f53bd84-5ba9-4439-8e77-3e0c01952b27" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_ae762309-5276-43c4-b127-2e205800f747" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_4f2b83ee-a0b4-42f5-ba5b-817a285afa9c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1f53bd84-5ba9-4439-8e77-3e0c01952b27" xlink:to="loc_us-gaap_EarningsPerShareBasic_4f2b83ee-a0b4-42f5-ba5b-817a285afa9c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_dd621a97-a026-42a1-a006-a2e12e286bf3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1f53bd84-5ba9-4439-8e77-3e0c01952b27" xlink:to="loc_us-gaap_EarningsPerShareDiluted_dd621a97-a026-42a1-a006-a2e12e286bf3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_2214c384-351a-4d79-b3d3-f2e5ef5ce2d9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1f53bd84-5ba9-4439-8e77-3e0c01952b27" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_2214c384-351a-4d79-b3d3-f2e5ef5ce2d9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_c6a50eb6-0bce-4287-a856-590efcdcb3a7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_2214c384-351a-4d79-b3d3-f2e5ef5ce2d9" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_c6a50eb6-0bce-4287-a856-590efcdcb3a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_c6a50eb6-0bce-4287-a856-590efcdcb3a7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_c6a50eb6-0bce-4287-a856-590efcdcb3a7" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_c6a50eb6-0bce-4287-a856-590efcdcb3a7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_11cd09c7-3634-49d1-8e43-e411756f450c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_c6a50eb6-0bce-4287-a856-590efcdcb3a7" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_11cd09c7-3634-49d1-8e43-e411756f450c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_5e0633ac-fe9b-47c2-920d-c5f4eb8e0f3c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_11cd09c7-3634-49d1-8e43-e411756f450c" xlink:to="loc_us-gaap_ConvertibleDebtMember_5e0633ac-fe9b-47c2-920d-c5f4eb8e0f3c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_5a1afdc0-93e3-457d-912a-a042d5a7e088" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_2214c384-351a-4d79-b3d3-f2e5ef5ce2d9" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_5a1afdc0-93e3-457d-912a-a042d5a7e088" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_5a1afdc0-93e3-457d-912a-a042d5a7e088_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_5a1afdc0-93e3-457d-912a-a042d5a7e088" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_5a1afdc0-93e3-457d-912a-a042d5a7e088_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_b7a731ad-f977-4ae7-b604-b00bf0a0b446" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_5a1afdc0-93e3-457d-912a-a042d5a7e088" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_b7a731ad-f977-4ae7-b604-b00bf0a0b446" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_7147022a-d0a4-42a9-837a-4e60caccff12" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_b7a731ad-f977-4ae7-b604-b00bf0a0b446" xlink:to="loc_us-gaap_EmployeeStockOptionMember_7147022a-d0a4-42a9-837a-4e60caccff12" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/CompositionofBalanceSheetItemsAccountsReceivablesDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#CompositionofBalanceSheetItemsAccountsReceivablesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CompositionofBalanceSheetItemsAccountsReceivablesDetails" xlink:type="extended" id="id597dc3e1a574de989b00710a5a88010_CompositionofBalanceSheetItemsAccountsReceivablesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_01a3e104-006f-4429-a7f1-4249ec0c5672" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_add4d8cc-6679-4188-bf22-e4aa6def87d8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_01a3e104-006f-4429-a7f1-4249ec0c5672" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_add4d8cc-6679-4188-bf22-e4aa6def87d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_63fd8b4e-c2e1-4156-b6d5-2ab7c6a386e5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_01a3e104-006f-4429-a7f1-4249ec0c5672" xlink:to="loc_us-gaap_ConcentrationRiskTable_63fd8b4e-c2e1-4156-b6d5-2ab7c6a386e5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_6596bd81-9e13-46e2-8d03-2307306e2a3f" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_63fd8b4e-c2e1-4156-b6d5-2ab7c6a386e5" xlink:to="loc_srt_ProductOrServiceAxis_6596bd81-9e13-46e2-8d03-2307306e2a3f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_6596bd81-9e13-46e2-8d03-2307306e2a3f_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_6596bd81-9e13-46e2-8d03-2307306e2a3f" xlink:to="loc_srt_ProductsAndServicesDomain_6596bd81-9e13-46e2-8d03-2307306e2a3f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_083828e6-b553-4431-bfba-c02eccfab6c1" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_6596bd81-9e13-46e2-8d03-2307306e2a3f" xlink:to="loc_srt_ProductsAndServicesDomain_083828e6-b553-4431-bfba-c02eccfab6c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_ThreeMajorCustomersMember_6cdae05b-690b-4ab6-9a3e-862d9ec17b97" xlink:href="supn-20210630.xsd#supn_ThreeMajorCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_083828e6-b553-4431-bfba-c02eccfab6c1" xlink:to="loc_supn_ThreeMajorCustomersMember_6cdae05b-690b-4ab6-9a3e-862d9ec17b97" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_47f3b8cc-a0c3-4992-8e6e-7f2f9c15990b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_63fd8b4e-c2e1-4156-b6d5-2ab7c6a386e5" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_47f3b8cc-a0c3-4992-8e6e-7f2f9c15990b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_47f3b8cc-a0c3-4992-8e6e-7f2f9c15990b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_47f3b8cc-a0c3-4992-8e6e-7f2f9c15990b" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_47f3b8cc-a0c3-4992-8e6e-7f2f9c15990b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_eb800e1c-11ed-4d80-a4ba-2a4da45cb02a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_47f3b8cc-a0c3-4992-8e6e-7f2f9c15990b" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_eb800e1c-11ed-4d80-a4ba-2a4da45cb02a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_2586201d-dd1d-4635-83d4-3f452f66c572" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_eb800e1c-11ed-4d80-a4ba-2a4da45cb02a" xlink:to="loc_us-gaap_AccountsReceivableMember_2586201d-dd1d-4635-83d4-3f452f66c572" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_d5417bdd-2f3e-40a2-9916-d6d56b1179aa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_63fd8b4e-c2e1-4156-b6d5-2ab7c6a386e5" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_d5417bdd-2f3e-40a2-9916-d6d56b1179aa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_d5417bdd-2f3e-40a2-9916-d6d56b1179aa_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_d5417bdd-2f3e-40a2-9916-d6d56b1179aa" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_d5417bdd-2f3e-40a2-9916-d6d56b1179aa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_bb563e50-2d63-4d92-83ce-7bb4c2c14b96" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_d5417bdd-2f3e-40a2-9916-d6d56b1179aa" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_bb563e50-2d63-4d92-83ce-7bb4c2c14b96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_ce2f4d0d-e490-4c25-9b7f-4d9d665bcee1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_bb563e50-2d63-4d92-83ce-7bb4c2c14b96" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_ce2f4d0d-e490-4c25-9b7f-4d9d665bcee1" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/CompositionofBalanceSheetItemsInventoriesDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#CompositionofBalanceSheetItemsInventoriesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CompositionofBalanceSheetItemsInventoriesDetails" xlink:type="extended" id="i7167366b680844c2aa0dc3f368163880_CompositionofBalanceSheetItemsInventoriesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryLineItems_3028d2a4-048d-44dd-b703-ef78037e5eea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InventoryLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryWorkInProcessAndRawMaterialsNetOfReserves_6fe04372-5f53-4c2b-b954-344b4a0029fd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InventoryWorkInProcessAndRawMaterialsNetOfReserves"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InventoryLineItems_3028d2a4-048d-44dd-b703-ef78037e5eea" xlink:to="loc_us-gaap_InventoryWorkInProcessAndRawMaterialsNetOfReserves_6fe04372-5f53-4c2b-b954-344b4a0029fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryCurrentTable_ca5c6527-62ce-4327-919c-a8e9b7986eb8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InventoryCurrentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_InventoryLineItems_3028d2a4-048d-44dd-b703-ef78037e5eea" xlink:to="loc_us-gaap_InventoryCurrentTable_ca5c6527-62ce-4327-919c-a8e9b7986eb8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesInventoryAxis_eabf4f8e-ce0e-41dc-a270-d798ec4eb545" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PublicUtilitiesInventoryAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_InventoryCurrentTable_ca5c6527-62ce-4327-919c-a8e9b7986eb8" xlink:to="loc_us-gaap_PublicUtilitiesInventoryAxis_eabf4f8e-ce0e-41dc-a270-d798ec4eb545" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_eabf4f8e-ce0e-41dc-a270-d798ec4eb545_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PublicUtilitiesInventoryTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PublicUtilitiesInventoryAxis_eabf4f8e-ce0e-41dc-a270-d798ec4eb545" xlink:to="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_eabf4f8e-ce0e-41dc-a270-d798ec4eb545_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_07bbd0fe-c78c-463b-b489-67d8bd7753e8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PublicUtilitiesInventoryTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PublicUtilitiesInventoryAxis_eabf4f8e-ce0e-41dc-a270-d798ec4eb545" xlink:to="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_07bbd0fe-c78c-463b-b489-67d8bd7753e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_ProductCandidatesMember_d6c9e34a-c1a2-4e30-a8d9-ec5e885f24d3" xlink:href="supn-20210630.xsd#supn_ProductCandidatesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PublicUtilitiesInventoryTypeDomain_07bbd0fe-c78c-463b-b489-67d8bd7753e8" xlink:to="loc_supn_ProductCandidatesMember_d6c9e34a-c1a2-4e30-a8d9-ec5e885f24d3" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/CompositionofBalanceSheetItemsPropertyandEquipmentDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#CompositionofBalanceSheetItemsPropertyandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CompositionofBalanceSheetItemsPropertyandEquipmentDetails" xlink:type="extended" id="id0ecb2ff054f4017a68772c28f04eccd_CompositionofBalanceSheetItemsPropertyandEquipmentDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c181967b-8e28-4980-8ff8-279c0909e514" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_ceeab33a-7ae5-428d-a8af-328f5f58eff2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c181967b-8e28-4980-8ff8-279c0909e514" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_ceeab33a-7ae5-428d-a8af-328f5f58eff2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization_b5f10e13-158a-4a8c-b77b-509a2d0e29fc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c181967b-8e28-4980-8ff8-279c0909e514" xlink:to="loc_us-gaap_FinanceLeaseRightOfUseAssetBeforeAccumulatedAmortization_b5f10e13-158a-4a8c-b77b-509a2d0e29fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization_aa601736-46fc-4482-8b03-b070b8d89dc7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c181967b-8e28-4980-8ff8-279c0909e514" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization_aa601736-46fc-4482-8b03-b070b8d89dc7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_52d65606-e898-4f92-9c50-982b861c4f8b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c181967b-8e28-4980-8ff8-279c0909e514" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_52d65606-e898-4f92-9c50-982b861c4f8b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_e96fd4a9-dc89-4299-bfd5-fff6126500e1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c181967b-8e28-4980-8ff8-279c0909e514" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_e96fd4a9-dc89-4299-bfd5-fff6126500e1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_21d162d8-138f-45f2-9558-d56649a6e010" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c181967b-8e28-4980-8ff8-279c0909e514" xlink:to="loc_us-gaap_DepreciationAndAmortization_21d162d8-138f-45f2-9558-d56649a6e010" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_17e6c9ff-d309-40e4-923b-78ca990c02c5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c181967b-8e28-4980-8ff8-279c0909e514" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_17e6c9ff-d309-40e4-923b-78ca990c02c5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_4e547afb-8f5c-4da3-a038-82aa4e6d0355" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_17e6c9ff-d309-40e4-923b-78ca990c02c5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_4e547afb-8f5c-4da3-a038-82aa4e6d0355" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_4e547afb-8f5c-4da3-a038-82aa4e6d0355_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_4e547afb-8f5c-4da3-a038-82aa4e6d0355" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_4e547afb-8f5c-4da3-a038-82aa4e6d0355_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_a99785f1-d039-400d-bc1f-583a5ce6c346" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_4e547afb-8f5c-4da3-a038-82aa4e6d0355" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_a99785f1-d039-400d-bc1f-583a5ce6c346" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_LabEquipmentAndFurnitureMember_9b0ef6e4-0e1e-4d3d-a31f-fe0b859487e3" xlink:href="supn-20210630.xsd#supn_LabEquipmentAndFurnitureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_a99785f1-d039-400d-bc1f-583a5ce6c346" xlink:to="loc_supn_LabEquipmentAndFurnitureMember_9b0ef6e4-0e1e-4d3d-a31f-fe0b859487e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_da739868-3ceb-4f0d-b6a7-8d6f10032ce6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_a99785f1-d039-400d-bc1f-583a5ce6c346" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_da739868-3ceb-4f0d-b6a7-8d6f10032ce6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_a175c6bd-8614-4b54-8ed9-9b23c564ef35" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ComputerSoftwareIntangibleAssetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_a99785f1-d039-400d-bc1f-583a5ce6c346" xlink:to="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_a175c6bd-8614-4b54-8ed9-9b23c564ef35" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_c44d1009-3324-4591-9019-8552a3345b53" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_a99785f1-d039-400d-bc1f-583a5ce6c346" xlink:to="loc_us-gaap_ComputerEquipmentMember_c44d1009-3324-4591-9019-8552a3345b53" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="supn-20210630.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CommitmentsandContingenciesDetails" xlink:type="extended" id="ie3bb38df63ab4876b379bee8838dc84c_CommitmentsandContingenciesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentLineItems_aea8e6f1-e251-4ce8-86c3-d97827a19a7d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermPurchaseCommitmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_NonRecourseDebtSaleOfFutureRoyaltiesNoncurrent_7d8e5266-da2b-47ef-89e2-f16dc06a2a03" xlink:href="supn-20210630.xsd#supn_NonRecourseDebtSaleOfFutureRoyaltiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_aea8e6f1-e251-4ce8-86c3-d97827a19a7d" xlink:to="loc_supn_NonRecourseDebtSaleOfFutureRoyaltiesNoncurrent_7d8e5266-da2b-47ef-89e2-f16dc06a2a03" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_PurchaseCommitmentAnnualMinimumAmountCommitted_a6f0f171-8877-4a8a-9b92-9f0b7cbf0d77" xlink:href="supn-20210630.xsd#supn_PurchaseCommitmentAnnualMinimumAmountCommitted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_aea8e6f1-e251-4ce8-86c3-d97827a19a7d" xlink:to="loc_supn_PurchaseCommitmentAnnualMinimumAmountCommitted_a6f0f171-8877-4a8a-9b92-9f0b7cbf0d77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermPurchaseCommitmentPeriod_5ec4f53a-bda0-4454-947c-de070e574ed0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongtermPurchaseCommitmentPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_aea8e6f1-e251-4ce8-86c3-d97827a19a7d" xlink:to="loc_us-gaap_LongtermPurchaseCommitmentPeriod_5ec4f53a-bda0-4454-947c-de070e574ed0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_PurchaseCommitmentRemainingMinimumAmountCommittedDueInNextThreeMonths_d9a675f8-2306-468f-8d3a-c847ec35c305" xlink:href="supn-20210630.xsd#supn_PurchaseCommitmentRemainingMinimumAmountCommittedDueInNextThreeMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_aea8e6f1-e251-4ce8-86c3-d97827a19a7d" xlink:to="loc_supn_PurchaseCommitmentRemainingMinimumAmountCommittedDueInNextThreeMonths_d9a675f8-2306-468f-8d3a-c847ec35c305" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_7df65c98-3844-4e24-a81b-77097c8e0d54" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LitigationSettlementAmountAwardedToOtherParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_aea8e6f1-e251-4ce8-86c3-d97827a19a7d" xlink:to="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_7df65c98-3844-4e24-a81b-77097c8e0d54" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermPurchaseCommitmentTable_451725ff-0d26-44ed-bbe9-09e5c29a2a45" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermPurchaseCommitmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentLineItems_aea8e6f1-e251-4ce8-86c3-d97827a19a7d" xlink:to="loc_us-gaap_LongTermPurchaseCommitmentTable_451725ff-0d26-44ed-bbe9-09e5c29a2a45" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_8b5c4da1-72b8-4454-a5c5-471bcb93f94a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_451725ff-0d26-44ed-bbe9-09e5c29a2a45" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_8b5c4da1-72b8-4454-a5c5-471bcb93f94a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8b5c4da1-72b8-4454-a5c5-471bcb93f94a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_8b5c4da1-72b8-4454-a5c5-471bcb93f94a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8b5c4da1-72b8-4454-a5c5-471bcb93f94a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_7abafc18-cb92-474c-bc43-fdbddea245f2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_8b5c4da1-72b8-4454-a5c5-471bcb93f94a" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_7abafc18-cb92-474c-bc43-fdbddea245f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_05ee90f5-8a9a-4028-93be-2f105c3a1472" xlink:href="supn-20210630.xsd#supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_7abafc18-cb92-474c-bc43-fdbddea245f2" xlink:to="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_05ee90f5-8a9a-4028-93be-2f105c3a1472" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_6189672b-ed6c-443d-b889-3e6a08526b45" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LongTermPurchaseCommitmentTable_451725ff-0d26-44ed-bbe9-09e5c29a2a45" xlink:to="loc_dei_LegalEntityAxis_6189672b-ed6c-443d-b889-3e6a08526b45" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_6189672b-ed6c-443d-b889-3e6a08526b45_default" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_6189672b-ed6c-443d-b889-3e6a08526b45" xlink:to="loc_dei_EntityDomain_6189672b-ed6c-443d-b889-3e6a08526b45_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_4cf7e8dc-f589-4297-b2cb-2b4db4b07881" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_6189672b-ed6c-443d-b889-3e6a08526b45" xlink:to="loc_dei_EntityDomain_4cf7e8dc-f589-4297-b2cb-2b4db4b07881" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_d7606821-4698-44aa-afe5-74985bb7aaca" xlink:href="supn-20210630.xsd#supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_4cf7e8dc-f589-4297-b2cb-2b4db4b07881" xlink:to="loc_supn_MDDUSEnterprisesLLCFormerlyUSWMEnterprisesMember_d7606821-4698-44aa-afe5-74985bb7aaca" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-roles-2021-01-31.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_us-gaap_OtherAssetsNoncurrent" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet" xlink:type="arc" order="1"/>
  </link:definitionLink>
</link:linkbase>
