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

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2020 Workiva-->
<!--r:8610448b-c7a4-4b74-b32c-337e0720bc80,g:b1e9a0ed-0573-456f-86c6-13aa843e3d6f-->
<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/CoverPage" xlink:type="simple" xlink:href="supn-20200331.xsd#CoverPage"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CoverPage" xlink:type="extended" id="i1c56a51d47004611aded14ee15fcd81a_CoverPage"/>
  <link:roleRef roleURI="http://www.supernus.com/role/CondensedConsolidatedBalanceSheets" xlink:type="simple" xlink:href="supn-20200331.xsd#CondensedConsolidatedBalanceSheets"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CondensedConsolidatedBalanceSheets" xlink:type="extended" id="id4e61252f24f4b7882d7c70992af1832_CondensedConsolidatedBalanceSheets"/>
  <link:roleRef roleURI="http://www.supernus.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="supn-20200331.xsd#CondensedConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="extended" id="i83cf28dee94f48bc998324ee1a30df37_CondensedConsolidatedBalanceSheetsParenthetical"/>
  <link:roleRef roleURI="http://www.supernus.com/role/CondensedConsolidatedStatementsofEarnings" xlink:type="simple" xlink:href="supn-20200331.xsd#CondensedConsolidatedStatementsofEarnings"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CondensedConsolidatedStatementsofEarnings" xlink:type="extended" id="ie422b74277e04e6db09cb2afe4fd848d_CondensedConsolidatedStatementsofEarnings">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_7b29e520-856a-44e1-abb4-973367cbfaef" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_c37264f2-830f-42e7-86ec-48636d5bc00f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7b29e520-856a-44e1-abb4-973367cbfaef" xlink:to="loc_us-gaap_RevenuesAbstract_c37264f2-830f-42e7-86ec-48636d5bc00f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_0a45d8f8-866d-40ce-b5d3-3104efc7019d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_c37264f2-830f-42e7-86ec-48636d5bc00f" xlink:to="loc_us-gaap_Revenues_0a45d8f8-866d-40ce-b5d3-3104efc7019d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_5bee4141-39f3-418b-a3cf-95359d894c32" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7b29e520-856a-44e1-abb4-973367cbfaef" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_5bee4141-39f3-418b-a3cf-95359d894c32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_b8c1f403-e85b-4962-ab04-8ca856298a0c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_5bee4141-39f3-418b-a3cf-95359d894c32" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_b8c1f403-e85b-4962-ab04-8ca856298a0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_71855474-e498-4480-ab69-bb23af751127" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_5bee4141-39f3-418b-a3cf-95359d894c32" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_71855474-e498-4480-ab69-bb23af751127" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_cf7b969a-c77b-49d2-b817-5946dec5d13e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_5bee4141-39f3-418b-a3cf-95359d894c32" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_cf7b969a-c77b-49d2-b817-5946dec5d13e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_20cb13c2-c02f-4d4d-8bb9-0da053f64514" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_5bee4141-39f3-418b-a3cf-95359d894c32" xlink:to="loc_us-gaap_CostsAndExpenses_20cb13c2-c02f-4d4d-8bb9-0da053f64514" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_4b870eb6-5a45-4bfa-b02b-dad25d451965" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7b29e520-856a-44e1-abb4-973367cbfaef" xlink:to="loc_us-gaap_OperatingIncomeLoss_4b870eb6-5a45-4bfa-b02b-dad25d451965" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_34413781-317d-4c1b-9011-7b1a6fe239ac" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7b29e520-856a-44e1-abb4-973367cbfaef" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_34413781-317d-4c1b-9011-7b1a6fe239ac" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingExpense_1fff1ae9-fea7-422c-a116-f12cc6eb272e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherNonoperatingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_34413781-317d-4c1b-9011-7b1a6fe239ac" xlink:to="loc_us-gaap_OtherNonoperatingExpense_1fff1ae9-fea7-422c-a116-f12cc6eb272e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncome_d3ddce8e-55c2-44f8-aa41-b213076a067d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherNonoperatingIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_34413781-317d-4c1b-9011-7b1a6fe239ac" xlink:to="loc_us-gaap_OtherNonoperatingIncome_d3ddce8e-55c2-44f8-aa41-b213076a067d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_16fdd5b2-4402-41c9-b60e-3449be6a51cc" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherNonoperatingIncomeExpenseAbstract_34413781-317d-4c1b-9011-7b1a6fe239ac" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_16fdd5b2-4402-41c9-b60e-3449be6a51cc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_05ce1f84-c6e1-40f6-8155-879d38749dd2" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7b29e520-856a-44e1-abb4-973367cbfaef" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_05ce1f84-c6e1-40f6-8155-879d38749dd2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_d7df0833-c65c-4f8b-9df1-ed750d3c29ce" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7b29e520-856a-44e1-abb4-973367cbfaef" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_d7df0833-c65c-4f8b-9df1-ed750d3c29ce" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_a5b13b2d-4c1e-4c7f-b8ec-d559abeea1f4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7b29e520-856a-44e1-abb4-973367cbfaef" xlink:to="loc_us-gaap_NetIncomeLoss_a5b13b2d-4c1e-4c7f-b8ec-d559abeea1f4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_a26cd1fb-6ab5-45c1-bd9b-1f43efa08fa2" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EarningsPerShareBasicAndDilutedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7b29e520-856a-44e1-abb4-973367cbfaef" xlink:to="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_a26cd1fb-6ab5-45c1-bd9b-1f43efa08fa2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_d9f395a7-1a6f-4367-8304-eab639ad1b4c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_a26cd1fb-6ab5-45c1-bd9b-1f43efa08fa2" xlink:to="loc_us-gaap_EarningsPerShareBasic_d9f395a7-1a6f-4367-8304-eab639ad1b4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_6ea692fc-7e11-48c1-808b-d1c58ce8f247" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAndDilutedAbstract_a26cd1fb-6ab5-45c1-bd9b-1f43efa08fa2" xlink:to="loc_us-gaap_EarningsPerShareDiluted_6ea692fc-7e11-48c1-808b-d1c58ce8f247" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_c84644c1-feb5-4d0c-a1df-78e93a580925" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_7b29e520-856a-44e1-abb4-973367cbfaef" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_c84644c1-feb5-4d0c-a1df-78e93a580925" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_1decb194-5fd8-441d-9827-0a3f15e3505c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_c84644c1-feb5-4d0c-a1df-78e93a580925" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_1decb194-5fd8-441d-9827-0a3f15e3505c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_26697ef1-db2e-430c-9f17-d84487a0c3f3" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_c84644c1-feb5-4d0c-a1df-78e93a580925" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_26697ef1-db2e-430c-9f17-d84487a0c3f3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_956cc670-306a-46dc-bb77-6ea94bbfa7b7" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_7b29e520-856a-44e1-abb4-973367cbfaef" xlink:to="loc_us-gaap_StatementTable_956cc670-306a-46dc-bb77-6ea94bbfa7b7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_cfb451a6-ac7e-46e2-9cf6-41f552f1afb1" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_956cc670-306a-46dc-bb77-6ea94bbfa7b7" xlink:to="loc_srt_ProductOrServiceAxis_cfb451a6-ac7e-46e2-9cf6-41f552f1afb1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_cfb451a6-ac7e-46e2-9cf6-41f552f1afb1_default" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_cfb451a6-ac7e-46e2-9cf6-41f552f1afb1" xlink:to="loc_srt_ProductsAndServicesDomain_cfb451a6-ac7e-46e2-9cf6-41f552f1afb1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_390531de-2271-4d93-b757-ee5fd2d8afe3" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_cfb451a6-ac7e-46e2-9cf6-41f552f1afb1" xlink:to="loc_srt_ProductsAndServicesDomain_390531de-2271-4d93-b757-ee5fd2d8afe3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_65cc8894-0092-49a3-8c59-00839cc2fb06" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_390531de-2271-4d93-b757-ee5fd2d8afe3" xlink:to="loc_us-gaap_ProductMember_65cc8894-0092-49a3-8c59-00839cc2fb06" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RoyaltyMember_fce31012-1f3f-4c0a-bf53-19e3fea08a7a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RoyaltyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_390531de-2271-4d93-b757-ee5fd2d8afe3" xlink:to="loc_us-gaap_RoyaltyMember_fce31012-1f3f-4c0a-bf53-19e3fea08a7a" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/CondensedConsolidatedStatementsofComprehensiveEarnings" xlink:type="simple" xlink:href="supn-20200331.xsd#CondensedConsolidatedStatementsofComprehensiveEarnings"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CondensedConsolidatedStatementsofComprehensiveEarnings" xlink:type="extended" id="i14048e5196274686b5e32084f4d6b224_CondensedConsolidatedStatementsofComprehensiveEarnings"/>
  <link:roleRef roleURI="http://www.supernus.com/role/CondensedConsolidatedStatementsofChangesinStockholdersEquity" xlink:type="simple" xlink:href="supn-20200331.xsd#CondensedConsolidatedStatementsofChangesinStockholdersEquity"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CondensedConsolidatedStatementsofChangesinStockholdersEquity" xlink:type="extended" id="i54cb1603a1ab44d49fd6780978527184_CondensedConsolidatedStatementsofChangesinStockholdersEquity">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_0609a624-3f4d-4bfe-b834-80cf110ecdcb" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5adfccf4-4e37-4080-9db4-3cd2147dca8f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_0609a624-3f4d-4bfe-b834-80cf110ecdcb" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5adfccf4-4e37-4080-9db4-3cd2147dca8f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_4911bb55-4f20-4c59-83bf-64644456f033" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5adfccf4-4e37-4080-9db4-3cd2147dca8f" xlink:to="loc_us-gaap_SharesOutstanding_4911bb55-4f20-4c59-83bf-64644456f033" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_a03c4be0-df02-4b54-bc07-2526d23edaa4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5adfccf4-4e37-4080-9db4-3cd2147dca8f" xlink:to="loc_us-gaap_StockholdersEquity_a03c4be0-df02-4b54-bc07-2526d23edaa4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_b32cc146-8dd1-4100-85f2-40a31d096822" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5adfccf4-4e37-4080-9db4-3cd2147dca8f" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_b32cc146-8dd1-4100-85f2-40a31d096822" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_StockIssuedDuringPeriodSharesStockOptionsAndWarrantsExercised_cabb074b-36e8-4f5a-8aa7-3b78e2a5a75e" xlink:href="supn-20200331.xsd#supn_StockIssuedDuringPeriodSharesStockOptionsAndWarrantsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5adfccf4-4e37-4080-9db4-3cd2147dca8f" xlink:to="loc_supn_StockIssuedDuringPeriodSharesStockOptionsAndWarrantsExercised_cabb074b-36e8-4f5a-8aa7-3b78e2a5a75e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_StockIssuedDuringPeriodValueStockOptionsAndWarrantsExercised_1def6eb3-6ffe-4656-a087-fa60dc36e19a" xlink:href="supn-20200331.xsd#supn_StockIssuedDuringPeriodValueStockOptionsAndWarrantsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5adfccf4-4e37-4080-9db4-3cd2147dca8f" xlink:to="loc_supn_StockIssuedDuringPeriodValueStockOptionsAndWarrantsExercised_1def6eb3-6ffe-4656-a087-fa60dc36e19a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_e7def781-fbbe-4bb8-b2a4-b8d335a204c4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5adfccf4-4e37-4080-9db4-3cd2147dca8f" xlink:to="loc_us-gaap_NetIncomeLoss_e7def781-fbbe-4bb8-b2a4-b8d335a204c4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent_0b25b07e-6c60-4b4b-ae1a-b5e9580a6866" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_5adfccf4-4e37-4080-9db4-3cd2147dca8f" xlink:to="loc_us-gaap_OtherComprehensiveIncomeAvailableforsaleSecuritiesAdjustmentNetOfTaxPortionAttributableToParent_0b25b07e-6c60-4b4b-ae1a-b5e9580a6866" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_efb512e3-92d3-4ff2-8965-1042f2beb80a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_fa636622-5da8-4798-a9fc-b12a1770a0cc" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_aaafffb8-8705-44fa-90d2-19acfc814f06" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_0609a624-3f4d-4bfe-b834-80cf110ecdcb" xlink:to="loc_us-gaap_StatementTable_aaafffb8-8705-44fa-90d2-19acfc814f06" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_49cff44c-1c53-47a0-8a75-0630684f9c24" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_aaafffb8-8705-44fa-90d2-19acfc814f06" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_49cff44c-1c53-47a0-8a75-0630684f9c24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_49cff44c-1c53-47a0-8a75-0630684f9c24_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_49cff44c-1c53-47a0-8a75-0630684f9c24" xlink:to="loc_us-gaap_EquityComponentDomain_49cff44c-1c53-47a0-8a75-0630684f9c24_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_cf79d69f-a970-43ae-8b99-d2cb832063c7" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_49cff44c-1c53-47a0-8a75-0630684f9c24" xlink:to="loc_us-gaap_EquityComponentDomain_cf79d69f-a970-43ae-8b99-d2cb832063c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_3dfc90d0-b0dc-480c-8ba3-35ecae0ffc26" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_cf79d69f-a970-43ae-8b99-d2cb832063c7" xlink:to="loc_us-gaap_CommonStockMember_3dfc90d0-b0dc-480c-8ba3-35ecae0ffc26" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_defe549d-83a3-432f-a26e-6fed3fd0dc2e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_cf79d69f-a970-43ae-8b99-d2cb832063c7" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_defe549d-83a3-432f-a26e-6fed3fd0dc2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_42ca5f0d-80a3-4f8d-ae42-6d2892ae4e01" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_cf79d69f-a970-43ae-8b99-d2cb832063c7" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_42ca5f0d-80a3-4f8d-ae42-6d2892ae4e01" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_cc3f8ae1-84ab-441b-912f-9810f7119763" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_cf79d69f-a970-43ae-8b99-d2cb832063c7" xlink:to="loc_us-gaap_RetainedEarningsMember_cc3f8ae1-84ab-441b-912f-9810f7119763" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="simple" xlink:href="supn-20200331.xsd#CondensedConsolidatedStatementsofCashFlows"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="extended" id="i9f8b2f1979c84cafaf1eb2eafbb1c439_CondensedConsolidatedStatementsofCashFlows"/>
  <link:roleRef roleURI="http://www.supernus.com/role/OrganizationandBusiness" xlink:type="simple" xlink:href="supn-20200331.xsd#OrganizationandBusiness"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/OrganizationandBusiness" xlink:type="extended" id="i70117bcf80eb4f7285b8b543895c5702_OrganizationandBusiness"/>
  <link:roleRef roleURI="http://www.supernus.com/role/OrganizationandBusinessDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#OrganizationandBusinessDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/OrganizationandBusinessDetails" xlink:type="extended" id="i84171e446f934b4ca040b090d857f14e_OrganizationandBusinessDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/SummaryofSignificantAccountingPolicies" xlink:type="simple" xlink:href="supn-20200331.xsd#SummaryofSignificantAccountingPolicies"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/SummaryofSignificantAccountingPolicies" xlink:type="extended" id="ic619e18ba2d54a14bf98e2df447b3cda_SummaryofSignificantAccountingPolicies"/>
  <link:roleRef roleURI="http://www.supernus.com/role/SummaryofSignificantAccountingPoliciesPolicies" xlink:type="simple" xlink:href="supn-20200331.xsd#SummaryofSignificantAccountingPoliciesPolicies"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/SummaryofSignificantAccountingPoliciesPolicies" xlink:type="extended" id="i63aa947f580a4941bd9480c1139b86d9_SummaryofSignificantAccountingPoliciesPolicies"/>
  <link:roleRef roleURI="http://www.supernus.com/role/SummaryofSignificantAccountingPoliciesBasisofPresentationDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#SummaryofSignificantAccountingPoliciesBasisofPresentationDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/SummaryofSignificantAccountingPoliciesBasisofPresentationDetails" xlink:type="extended" id="if1f8a3922ea94afe933c9fb9582d5e35_SummaryofSignificantAccountingPoliciesBasisofPresentationDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/SummaryofSignificantAccountingPoliciesRevenueRecognitionDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#SummaryofSignificantAccountingPoliciesRevenueRecognitionDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/SummaryofSignificantAccountingPoliciesRevenueRecognitionDetails" xlink:type="extended" id="i7aa380c08b694a8388e62cbf518bc473_SummaryofSignificantAccountingPoliciesRevenueRecognitionDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_4832e586-064c-45f9-84e5-14253e75510f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_SalesReturnPeriodPriorToExpiration_d1340ba6-ce28-4c55-af78-f9829e29b58a" xlink:href="supn-20200331.xsd#supn_SalesReturnPeriodPriorToExpiration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_4832e586-064c-45f9-84e5-14253e75510f" xlink:to="loc_supn_SalesReturnPeriodPriorToExpiration_d1340ba6-ce28-4c55-af78-f9829e29b58a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_SalesReturnPeriod_f7e860f7-862b-4c61-85a0-2ba22b163822" xlink:href="supn-20200331.xsd#supn_SalesReturnPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_4832e586-064c-45f9-84e5-14253e75510f" xlink:to="loc_supn_SalesReturnPeriod_f7e860f7-862b-4c61-85a0-2ba22b163822" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_NumberOfProprietaryCommercialProducts_6a142cc7-efa4-49e7-aa1b-bc223758c2e3" xlink:href="supn-20200331.xsd#supn_NumberOfProprietaryCommercialProducts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_4832e586-064c-45f9-84e5-14253e75510f" xlink:to="loc_supn_NumberOfProprietaryCommercialProducts_6a142cc7-efa4-49e7-aa1b-bc223758c2e3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_ProductsShelfLife_46c9a921-cb5e-4603-805c-271b61f867c3" xlink:href="supn-20200331.xsd#supn_ProductsShelfLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_4832e586-064c-45f9-84e5-14253e75510f" xlink:to="loc_supn_ProductsShelfLife_46c9a921-cb5e-4603-805c-271b61f867c3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_MinimumGuaranteedAmountsOwedToCompany_b56740b9-3631-4b3e-bea0-974b5603fc32" xlink:href="supn-20200331.xsd#supn_MinimumGuaranteedAmountsOwedToCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_4832e586-064c-45f9-84e5-14253e75510f" xlink:to="loc_supn_MinimumGuaranteedAmountsOwedToCompany_b56740b9-3631-4b3e-bea0-974b5603fc32" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_5740f384-588a-4d71-bb01-6046d68687e2" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_4832e586-064c-45f9-84e5-14253e75510f" xlink:to="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_5740f384-588a-4d71-bb01-6046d68687e2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_48e10c75-515c-4d06-aa9d-a01037f4c159" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_5740f384-588a-4d71-bb01-6046d68687e2" xlink:to="loc_us-gaap_TypeOfArrangementAxis_48e10c75-515c-4d06-aa9d-a01037f4c159" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_48e10c75-515c-4d06-aa9d-a01037f4c159_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_48e10c75-515c-4d06-aa9d-a01037f4c159" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_48e10c75-515c-4d06-aa9d-a01037f4c159_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_7a186edc-8b0a-42a0-8d7a-c0785c95bd62" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_48e10c75-515c-4d06-aa9d-a01037f4c159" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_7a186edc-8b0a-42a0-8d7a-c0785c95bd62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollaborativeArrangementMember_c10985a1-a2a1-455a-a20d-18e27a79e6f6" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CollaborativeArrangementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_7a186edc-8b0a-42a0-8d7a-c0785c95bd62" xlink:to="loc_us-gaap_CollaborativeArrangementMember_c10985a1-a2a1-455a-a20d-18e27a79e6f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RoyaltyAgreementsMember_5e64d681-f0e4-4c63-8f9c-549f0e9c7555" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RoyaltyAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_7a186edc-8b0a-42a0-8d7a-c0785c95bd62" xlink:to="loc_us-gaap_RoyaltyAgreementsMember_5e64d681-f0e4-4c63-8f9c-549f0e9c7555" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_5a70c7aa-02fb-44cb-83e4-c2da13947730" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_5740f384-588a-4d71-bb01-6046d68687e2" xlink:to="loc_srt_RangeAxis_5a70c7aa-02fb-44cb-83e4-c2da13947730" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_5a70c7aa-02fb-44cb-83e4-c2da13947730_default" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_5a70c7aa-02fb-44cb-83e4-c2da13947730" xlink:to="loc_srt_RangeMember_5a70c7aa-02fb-44cb-83e4-c2da13947730_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_ef2c0ffb-9546-4625-b124-7582316f87d6" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_5a70c7aa-02fb-44cb-83e4-c2da13947730" xlink:to="loc_srt_RangeMember_ef2c0ffb-9546-4625-b124-7582316f87d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_2492087d-5680-46ab-926b-351988aaa04a" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_ef2c0ffb-9546-4625-b124-7582316f87d6" xlink:to="loc_srt_MaximumMember_2492087d-5680-46ab-926b-351988aaa04a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/SummaryofSignificantAccountingPoliciesSharebasedCompensationDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#SummaryofSignificantAccountingPoliciesSharebasedCompensationDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/SummaryofSignificantAccountingPoliciesSharebasedCompensationDetails" xlink:type="extended" id="i75e1d378f8804c7f93aa73ef37e8e6ce_SummaryofSignificantAccountingPoliciesSharebasedCompensationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_43040efe-de64-415d-a616-b29ec1668d0c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_91f04a80-92de-4ae7-b07a-adf03e963c5d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_43040efe-de64-415d-a616-b29ec1668d0c" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_91f04a80-92de-4ae7-b07a-adf03e963c5d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_61573c3e-94a5-4672-906b-ef845875f679" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_43040efe-de64-415d-a616-b29ec1668d0c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_61573c3e-94a5-4672-906b-ef845875f679" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d2815f32-7346-4540-bbb5-9bdde71516e8" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_43040efe-de64-415d-a616-b29ec1668d0c" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d2815f32-7346-4540-bbb5-9bdde71516e8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_6273835f-8a67-41e3-8eac-0ddc11e04876" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d2815f32-7346-4540-bbb5-9bdde71516e8" xlink:to="loc_us-gaap_AwardTypeAxis_6273835f-8a67-41e3-8eac-0ddc11e04876" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6273835f-8a67-41e3-8eac-0ddc11e04876_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_6273835f-8a67-41e3-8eac-0ddc11e04876" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6273835f-8a67-41e3-8eac-0ddc11e04876_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6ae58dd7-1dd3-496b-b9e4-750756372f76" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_6273835f-8a67-41e3-8eac-0ddc11e04876" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6ae58dd7-1dd3-496b-b9e4-750756372f76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_f300434e-c26f-431a-979b-45178533b021" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6ae58dd7-1dd3-496b-b9e4-750756372f76" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_f300434e-c26f-431a-979b-45178533b021" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/SummaryofSignificantAccountingPoliciesAdvertisingExpenseDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#SummaryofSignificantAccountingPoliciesAdvertisingExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/SummaryofSignificantAccountingPoliciesAdvertisingExpenseDetails" xlink:type="extended" id="ia1175901640b4f0a92252c307f9cd155_SummaryofSignificantAccountingPoliciesAdvertisingExpenseDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_0f6f8a4e-c9d6-4abc-b432-f0a0bb0db172" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketingAndAdvertisingExpenseAbstract_fca280e8-4ac3-44eb-b59f-f4c9ec44dcd2" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MarketingAndAdvertisingExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_0f6f8a4e-c9d6-4abc-b432-f0a0bb0db172" xlink:to="loc_us-gaap_MarketingAndAdvertisingExpenseAbstract_fca280e8-4ac3-44eb-b59f-f4c9ec44dcd2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdvertisingExpense_ed9d4342-1321-4139-abd5-d9c66ee04242" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AdvertisingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketingAndAdvertisingExpenseAbstract_fca280e8-4ac3-44eb-b59f-f4c9ec44dcd2" xlink:to="loc_us-gaap_AdvertisingExpense_ed9d4342-1321-4139-abd5-d9c66ee04242" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_dde23ff5-54ba-4bf6-9796-3546715051ef" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_0f6f8a4e-c9d6-4abc-b432-f0a0bb0db172" xlink:to="loc_us-gaap_ConcentrationRiskTable_dde23ff5-54ba-4bf6-9796-3546715051ef" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_7fc215eb-990c-4b20-81eb-367f84a39e26" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_dde23ff5-54ba-4bf6-9796-3546715051ef" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_7fc215eb-990c-4b20-81eb-367f84a39e26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_7fc215eb-990c-4b20-81eb-367f84a39e26_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_7fc215eb-990c-4b20-81eb-367f84a39e26" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_7fc215eb-990c-4b20-81eb-367f84a39e26_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_b9208970-c5a2-4836-b50a-9ce73f340288" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_7fc215eb-990c-4b20-81eb-367f84a39e26" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_b9208970-c5a2-4836-b50a-9ce73f340288" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_ebceb002-a45d-492c-9727-21ca12f2cf80" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_b9208970-c5a2-4836-b50a-9ce73f340288" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_ebceb002-a45d-492c-9727-21ca12f2cf80" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/DisaggregatedRevenues" xlink:type="simple" xlink:href="supn-20200331.xsd#DisaggregatedRevenues"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/DisaggregatedRevenues" xlink:type="extended" id="ie130e0cd1a7f44189e070c2570b4a2e0_DisaggregatedRevenues"/>
  <link:roleRef roleURI="http://www.supernus.com/role/DisaggregatedRevenuesTables" xlink:type="simple" xlink:href="supn-20200331.xsd#DisaggregatedRevenuesTables"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/DisaggregatedRevenuesTables" xlink:type="extended" id="i3b5c63019e234145bf60f741dfe8a535_DisaggregatedRevenuesTables"/>
  <link:roleRef roleURI="http://www.supernus.com/role/DisaggregatedRevenuesSummaryofRevenuesDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#DisaggregatedRevenuesSummaryofRevenuesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/DisaggregatedRevenuesSummaryofRevenuesDetails" xlink:type="extended" id="i30caf50936fd4d4a96188b97bb91457e_DisaggregatedRevenuesSummaryofRevenuesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_2bca5eaf-ce9b-4242-9d95-af753703c4ce" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_f996b5c4-549c-47c8-9dc5-54027edb0cdb" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2bca5eaf-ce9b-4242-9d95-af753703c4ce" xlink:to="loc_us-gaap_Revenues_f996b5c4-549c-47c8-9dc5-54027edb0cdb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_86d4ecbe-e66b-4991-8d1c-8ae59d1ffaab" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_2bca5eaf-ce9b-4242-9d95-af753703c4ce" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_86d4ecbe-e66b-4991-8d1c-8ae59d1ffaab" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_20ed4d36-5e3c-460d-a019-38a1c3e5eee4" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_86d4ecbe-e66b-4991-8d1c-8ae59d1ffaab" xlink:to="loc_srt_ProductOrServiceAxis_20ed4d36-5e3c-460d-a019-38a1c3e5eee4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_20ed4d36-5e3c-460d-a019-38a1c3e5eee4_default" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_20ed4d36-5e3c-460d-a019-38a1c3e5eee4" xlink:to="loc_srt_ProductsAndServicesDomain_20ed4d36-5e3c-460d-a019-38a1c3e5eee4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_3cec9250-5b99-4e69-b39e-3c4ff3bd0018" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_20ed4d36-5e3c-460d-a019-38a1c3e5eee4" xlink:to="loc_srt_ProductsAndServicesDomain_3cec9250-5b99-4e69-b39e-3c4ff3bd0018" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_TrokendiXrMember_40e7d346-4316-4058-99ed-23d6898928ca" xlink:href="supn-20200331.xsd#supn_TrokendiXrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_3cec9250-5b99-4e69-b39e-3c4ff3bd0018" xlink:to="loc_supn_TrokendiXrMember_40e7d346-4316-4058-99ed-23d6898928ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_OxtellarXRMember_ca9b3ff9-8b45-44e0-918e-63ec692d53e6" xlink:href="supn-20200331.xsd#supn_OxtellarXRMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_3cec9250-5b99-4e69-b39e-3c4ff3bd0018" xlink:to="loc_supn_OxtellarXRMember_ca9b3ff9-8b45-44e0-918e-63ec692d53e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_838b0bac-aab6-467c-9752-91b7405e658f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_3cec9250-5b99-4e69-b39e-3c4ff3bd0018" xlink:to="loc_us-gaap_ProductMember_838b0bac-aab6-467c-9752-91b7405e658f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RoyaltyMember_fda9e41c-1788-4785-b500-d78b238eca79" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RoyaltyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_3cec9250-5b99-4e69-b39e-3c4ff3bd0018" xlink:to="loc_us-gaap_RoyaltyMember_fda9e41c-1788-4785-b500-d78b238eca79" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/DisaggregatedRevenuesDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#DisaggregatedRevenuesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/DisaggregatedRevenuesDetails" xlink:type="extended" id="i79ffe21cad824d0ead6cfea40ffe290b_DisaggregatedRevenuesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_b7ffe38d-bc12-451c-894b-d40f64ae7fe3" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_9edcd60d-6406-4033-8cef-e14ee358c6c4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_b7ffe38d-bc12-451c-894b-d40f64ae7fe3" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_9edcd60d-6406-4033-8cef-e14ee358c6c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_RevenueFromRoyaltyAgreement_f295f4f1-c361-4ef4-9607-1ec54428c656" xlink:href="supn-20200331.xsd#supn_RevenueFromRoyaltyAgreement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_b7ffe38d-bc12-451c-894b-d40f64ae7fe3" xlink:to="loc_supn_RevenueFromRoyaltyAgreement_f295f4f1-c361-4ef4-9607-1ec54428c656" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_RevenueFromContractWithCustomerProductsReturnsAllowance_f3f0b5f7-07ab-492f-b290-c500e1d5bdac" xlink:href="supn-20200331.xsd#supn_RevenueFromContractWithCustomerProductsReturnsAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_b7ffe38d-bc12-451c-894b-d40f64ae7fe3" xlink:to="loc_supn_RevenueFromContractWithCustomerProductsReturnsAllowance_f3f0b5f7-07ab-492f-b290-c500e1d5bdac" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_f3fc0e28-431a-436a-9d7b-01e64640c167" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_b7ffe38d-bc12-451c-894b-d40f64ae7fe3" xlink:to="loc_us-gaap_Revenues_f3fc0e28-431a-436a-9d7b-01e64640c167" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_d6feb357-2e9b-418f-b8fa-71c64347cec4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_b7ffe38d-bc12-451c-894b-d40f64ae7fe3" xlink:to="loc_us-gaap_NetIncomeLoss_d6feb357-2e9b-418f-b8fa-71c64347cec4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicAndDiluted_a4955fa6-7255-4d85-8412-09466108fe1a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EarningsPerShareBasicAndDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_b7ffe38d-bc12-451c-894b-d40f64ae7fe3" xlink:to="loc_us-gaap_EarningsPerShareBasicAndDiluted_a4955fa6-7255-4d85-8412-09466108fe1a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_f53e9d81-cac8-4d99-8177-c0bcded0153b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionLineItems_b7ffe38d-bc12-451c-894b-d40f64ae7fe3" xlink:to="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_f53e9d81-cac8-4d99-8177-c0bcded0153b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_3f31ff22-3a87-48d4-a006-23981e6af418" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_f53e9d81-cac8-4d99-8177-c0bcded0153b" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_3f31ff22-3a87-48d4-a006-23981e6af418" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_3f31ff22-3a87-48d4-a006-23981e6af418_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_3f31ff22-3a87-48d4-a006-23981e6af418" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_3f31ff22-3a87-48d4-a006-23981e6af418_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_9f6fe333-e04e-497b-a24c-0cb3a4f82f50" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_3f31ff22-3a87-48d4-a006-23981e6af418" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_9f6fe333-e04e-497b-a24c-0cb3a4f82f50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_9d966e63-733a-4fb0-a478-fe0e59df5d94" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_9f6fe333-e04e-497b-a24c-0cb3a4f82f50" xlink:to="loc_us-gaap_SalesRevenueNetMember_9d966e63-733a-4fb0-a478-fe0e59df5d94" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_d69eb2e4-e6a0-418e-a47a-d4abcdb188a6" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_f53e9d81-cac8-4d99-8177-c0bcded0153b" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_d69eb2e4-e6a0-418e-a47a-d4abcdb188a6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_d69eb2e4-e6a0-418e-a47a-d4abcdb188a6_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_d69eb2e4-e6a0-418e-a47a-d4abcdb188a6" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_d69eb2e4-e6a0-418e-a47a-d4abcdb188a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_1c45bb50-a181-4be0-893e-e7b8a4e2cdf4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_d69eb2e4-e6a0-418e-a47a-d4abcdb188a6" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_1c45bb50-a181-4be0-893e-e7b8a4e2cdf4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_9ba3cdf5-b248-460d-9462-aafce6dc65b7" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_1c45bb50-a181-4be0-893e-e7b8a4e2cdf4" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_9ba3cdf5-b248-460d-9462-aafce6dc65b7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_b27da951-e4c4-4f55-89db-1d10c1ce6ab9" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_f53e9d81-cac8-4d99-8177-c0bcded0153b" xlink:to="loc_srt_MajorCustomersAxis_b27da951-e4c4-4f55-89db-1d10c1ce6ab9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_b27da951-e4c4-4f55-89db-1d10c1ce6ab9_default" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_b27da951-e4c4-4f55-89db-1d10c1ce6ab9" xlink:to="loc_srt_NameOfMajorCustomerDomain_b27da951-e4c4-4f55-89db-1d10c1ce6ab9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_1eb8ab97-3664-4695-a69e-6f3cdaa14131" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_b27da951-e4c4-4f55-89db-1d10c1ce6ab9" xlink:to="loc_srt_NameOfMajorCustomerDomain_1eb8ab97-3664-4695-a69e-6f3cdaa14131" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_TrokendiXrMember_85cccecf-3558-41fa-b9cc-66104eea2934" xlink:href="supn-20200331.xsd#supn_TrokendiXrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_1eb8ab97-3664-4695-a69e-6f3cdaa14131" xlink:to="loc_supn_TrokendiXrMember_85cccecf-3558-41fa-b9cc-66104eea2934" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_d287c2a0-b066-45cd-86a2-84f7e39f137c" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_f53e9d81-cac8-4d99-8177-c0bcded0153b" xlink:to="loc_srt_ProductOrServiceAxis_d287c2a0-b066-45cd-86a2-84f7e39f137c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_d287c2a0-b066-45cd-86a2-84f7e39f137c_default" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_d287c2a0-b066-45cd-86a2-84f7e39f137c" xlink:to="loc_srt_ProductsAndServicesDomain_d287c2a0-b066-45cd-86a2-84f7e39f137c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_a6141be9-79a4-4c03-974e-16392132ed6c" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_d287c2a0-b066-45cd-86a2-84f7e39f137c" xlink:to="loc_srt_ProductsAndServicesDomain_a6141be9-79a4-4c03-974e-16392132ed6c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_TrokendiXrMember_153795ef-80c8-40f2-89c5-9b0ea56cb596" xlink:href="supn-20200331.xsd#supn_TrokendiXrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_a6141be9-79a4-4c03-974e-16392132ed6c" xlink:to="loc_supn_TrokendiXrMember_153795ef-80c8-40f2-89c5-9b0ea56cb596" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_bbab8977-92e9-49cf-a499-679489d6bf55" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ChangeInAccountingEstimateByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueInitialApplicationPeriodCumulativeEffectTransitionTable_f53e9d81-cac8-4d99-8177-c0bcded0153b" xlink:to="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_bbab8977-92e9-49cf-a499-679489d6bf55" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_bbab8977-92e9-49cf-a499-679489d6bf55_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ChangeInAccountingEstimateTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_bbab8977-92e9-49cf-a499-679489d6bf55" xlink:to="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_bbab8977-92e9-49cf-a499-679489d6bf55_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_6a2b1def-7ba8-4f4a-ba95-8ce34f865781" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ChangeInAccountingEstimateTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_bbab8977-92e9-49cf-a499-679489d6bf55" xlink:to="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_6a2b1def-7ba8-4f4a-ba95-8ce34f865781" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesReturnsAndAllowancesMember_0aba1879-756f-4be4-8f38-2eedad171564" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SalesReturnsAndAllowancesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_6a2b1def-7ba8-4f4a-ba95-8ce34f865781" xlink:to="loc_us-gaap_SalesReturnsAndAllowancesMember_0aba1879-756f-4be4-8f38-2eedad171564" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/FairValueofFinancialInstruments" xlink:type="simple" xlink:href="supn-20200331.xsd#FairValueofFinancialInstruments"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/FairValueofFinancialInstruments" xlink:type="extended" id="i6dba86658a4a401a8361a2d70fb6ee61_FairValueofFinancialInstruments"/>
  <link:roleRef roleURI="http://www.supernus.com/role/FairValueofFinancialInstrumentsTables" xlink:type="simple" xlink:href="supn-20200331.xsd#FairValueofFinancialInstrumentsTables"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/FairValueofFinancialInstrumentsTables" xlink:type="extended" id="i023bea2fde924c24b6c9832045ad076a_FairValueofFinancialInstrumentsTables"/>
  <link:roleRef roleURI="http://www.supernus.com/role/FairValueofFinancialInstrumentsNarrativeDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#FairValueofFinancialInstrumentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/FairValueofFinancialInstrumentsNarrativeDetails" xlink:type="extended" id="ic8b5d6d7e4534235a14cfd6c449955e6_FairValueofFinancialInstrumentsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_3f4369fb-eaef-4ada-a09a-2b8ac466173a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_3a01babe-6a3a-4d89-8e4f-1316b667359f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_3f4369fb-eaef-4ada-a09a-2b8ac466173a" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_3a01babe-6a3a-4d89-8e4f-1316b667359f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded_e7325eba-594a-4378-9aab-9346361aa252" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_3f4369fb-eaef-4ada-a09a-2b8ac466173a" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAllowanceForCreditLossNotPreviouslyRecorded_e7325eba-594a-4378-9aab-9346361aa252" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d186b74d-2470-4e23-926c-1a1b22400c3d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_3f4369fb-eaef-4ada-a09a-2b8ac466173a" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d186b74d-2470-4e23-926c-1a1b22400c3d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_33ef7df8-9282-43b1-abd8-7f3597bc656e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d186b74d-2470-4e23-926c-1a1b22400c3d" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_33ef7df8-9282-43b1-abd8-7f3597bc656e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_33ef7df8-9282-43b1-abd8-7f3597bc656e_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_33ef7df8-9282-43b1-abd8-7f3597bc656e" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_33ef7df8-9282-43b1-abd8-7f3597bc656e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_f361e4d8-c242-49b4-b03e-c8efcd016086" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_33ef7df8-9282-43b1-abd8-7f3597bc656e" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_f361e4d8-c242-49b4-b03e-c8efcd016086" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_622b99ef-a5ec-4d8d-b801-e5ff22be1bba" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_f361e4d8-c242-49b4-b03e-c8efcd016086" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_622b99ef-a5ec-4d8d-b801-e5ff22be1bba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0aa2c754-22e9-4095-984a-49915f98cec9" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_d186b74d-2470-4e23-926c-1a1b22400c3d" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0aa2c754-22e9-4095-984a-49915f98cec9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0aa2c754-22e9-4095-984a-49915f98cec9_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0aa2c754-22e9-4095-984a-49915f98cec9" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_0aa2c754-22e9-4095-984a-49915f98cec9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_6e987e71-d232-4054-b57c-ce3445730be1" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_0aa2c754-22e9-4095-984a-49915f98cec9" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_6e987e71-d232-4054-b57c-ce3445730be1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_8ca652c7-c71c-4bf1-a7cd-e5aa5cf725c7" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_6e987e71-d232-4054-b57c-ce3445730be1" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_8ca652c7-c71c-4bf1-a7cd-e5aa5cf725c7" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/FairValueofFinancialInstrumentsCarryingValueDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#FairValueofFinancialInstrumentsCarryingValueDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/FairValueofFinancialInstrumentsCarryingValueDetails" xlink:type="extended" id="i6c05d39e623e44e5ad7ff4c9f04bdd8e_FairValueofFinancialInstrumentsCarryingValueDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a005b2c6-6bf3-4b76-a9e7-ff04e2329099" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_b5972215-08c4-4ccd-8acc-9782f7570f5f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a005b2c6-6bf3-4b76-a9e7-ff04e2329099" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_b5972215-08c4-4ccd-8acc-9782f7570f5f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_396a39b5-98f6-419d-98c8-9587102c7ead" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_b5972215-08c4-4ccd-8acc-9782f7570f5f" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_396a39b5-98f6-419d-98c8-9587102c7ead" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesCurrentAbstract_92fe57a1-1166-4f2c-b784-4d72674b68a0" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtSecuritiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_b5972215-08c4-4ccd-8acc-9782f7570f5f" xlink:to="loc_us-gaap_DebtSecuritiesCurrentAbstract_92fe57a1-1166-4f2c-b784-4d72674b68a0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_441dc0bd-be74-40cc-b974-af73a899de69" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesCurrentAbstract_92fe57a1-1166-4f2c-b784-4d72674b68a0" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_441dc0bd-be74-40cc-b974-af73a899de69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesNoncurrentAbstract_83a7f8aa-de3f-4161-bc4b-f621b5859897" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtSecuritiesNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_b5972215-08c4-4ccd-8acc-9782f7570f5f" xlink:to="loc_us-gaap_DebtSecuritiesNoncurrentAbstract_83a7f8aa-de3f-4161-bc4b-f621b5859897" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent_38bd59af-a3cc-477e-968f-814be59b4bc0" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtSecuritiesNoncurrentAbstract_83a7f8aa-de3f-4161-bc4b-f621b5859897" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent_38bd59af-a3cc-477e-968f-814be59b4bc0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrentAbstract_8379d675-feac-4cfd-9201-7e3f1f0fc5f2" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_OtherAssetsNoncurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_b5972215-08c4-4ccd-8acc-9782f7570f5f" xlink:to="loc_us-gaap_OtherAssetsNoncurrentAbstract_8379d675-feac-4cfd-9201-7e3f1f0fc5f2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent_20f02ac3-66b5-485b-aec6-fb2b83a935c3" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherAssetsNoncurrentAbstract_8379d675-feac-4cfd-9201-7e3f1f0fc5f2" xlink:to="loc_us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent_20f02ac3-66b5-485b-aec6-fb2b83a935c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_328f9b81-aec0-4565-bc09-01766c4d3e04" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_b5972215-08c4-4ccd-8acc-9782f7570f5f" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_328f9b81-aec0-4565-bc09-01766c4d3e04" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_fba14d14-014b-4e78-9615-9612b953312e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_a005b2c6-6bf3-4b76-a9e7-ff04e2329099" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_fba14d14-014b-4e78-9615-9612b953312e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByAssetClassAxis_894310d8-c3c2-4d6d-968f-d666de72a5a9" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByAssetClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_fba14d14-014b-4e78-9615-9612b953312e" xlink:to="loc_us-gaap_FairValueByAssetClassAxis_894310d8-c3c2-4d6d-968f-d666de72a5a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_894310d8-c3c2-4d6d-968f-d666de72a5a9_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_894310d8-c3c2-4d6d-968f-d666de72a5a9" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_894310d8-c3c2-4d6d-968f-d666de72a5a9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_f2f41593-1af8-40c2-813a-e5b771180406" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByAssetClassAxis_894310d8-c3c2-4d6d-968f-d666de72a5a9" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_f2f41593-1af8-40c2-813a-e5b771180406" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashMember_18347591-cb43-490f-8eed-c050272bca9d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CashMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_f2f41593-1af8-40c2-813a-e5b771180406" xlink:to="loc_us-gaap_CashMember_18347591-cb43-490f-8eed-c050272bca9d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_ca39e3a3-f2ea-492e-b56c-2c89e4f8396f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationByAssetClassDomain_f2f41593-1af8-40c2-813a-e5b771180406" xlink:to="loc_us-gaap_MoneyMarketFundsMember_ca39e3a3-f2ea-492e-b56c-2c89e4f8396f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_059aabbf-4cff-4065-b681-249b5539f494" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_fba14d14-014b-4e78-9615-9612b953312e" xlink:to="loc_us-gaap_FinancialInstrumentAxis_059aabbf-4cff-4065-b681-249b5539f494" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_059aabbf-4cff-4065-b681-249b5539f494_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_059aabbf-4cff-4065-b681-249b5539f494" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_059aabbf-4cff-4065-b681-249b5539f494_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_c0b237ec-7775-47ae-bfe5-ec84e0a24e47" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_059aabbf-4cff-4065-b681-249b5539f494" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_c0b237ec-7775-47ae-bfe5-ec84e0a24e47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_9150aabd-c9a7-44ad-af75-3df918885fdc" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_c0b237ec-7775-47ae-bfe5-ec84e0a24e47" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_9150aabd-c9a7-44ad-af75-3df918885fdc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MunicipalBondsMember_70c6d7d7-15fd-4ba1-a482-c5652fb4517f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MunicipalBondsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_c0b237ec-7775-47ae-bfe5-ec84e0a24e47" xlink:to="loc_us-gaap_MunicipalBondsMember_70c6d7d7-15fd-4ba1-a482-c5652fb4517f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_73c36e3b-be8b-44a8-9852-b7a8ab6b48fa" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_c0b237ec-7775-47ae-bfe5-ec84e0a24e47" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_73c36e3b-be8b-44a8-9852-b7a8ab6b48fa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_e7f7dea6-5b96-468b-bad9-1b3752166dce" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_fba14d14-014b-4e78-9615-9612b953312e" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_e7f7dea6-5b96-468b-bad9-1b3752166dce" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_e7f7dea6-5b96-468b-bad9-1b3752166dce_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_e7f7dea6-5b96-468b-bad9-1b3752166dce" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_e7f7dea6-5b96-468b-bad9-1b3752166dce_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_fa497f02-bedb-4d97-a1f4-8a9c034d4d1e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_e7f7dea6-5b96-468b-bad9-1b3752166dce" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_fa497f02-bedb-4d97-a1f4-8a9c034d4d1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_3ecce136-d75b-4cd6-9ba4-c8bd37eeb9a6" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_fa497f02-bedb-4d97-a1f4-8a9c034d4d1e" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_3ecce136-d75b-4cd6-9ba4-c8bd37eeb9a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_a7ef20a7-5b51-4854-8593-b37b41320727" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_fba14d14-014b-4e78-9615-9612b953312e" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_a7ef20a7-5b51-4854-8593-b37b41320727" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_a7ef20a7-5b51-4854-8593-b37b41320727_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_a7ef20a7-5b51-4854-8593-b37b41320727" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_a7ef20a7-5b51-4854-8593-b37b41320727_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_602140af-9eb1-4185-a034-84943b7fdfe9" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_a7ef20a7-5b51-4854-8593-b37b41320727" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_602140af-9eb1-4185-a034-84943b7fdfe9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_4cf3f5d0-19c4-4308-b993-1012035b3e5c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_602140af-9eb1-4185-a034-84943b7fdfe9" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_4cf3f5d0-19c4-4308-b993-1012035b3e5c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_407b55b4-3aef-4dd1-aa8e-3dfcaef59d14" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_602140af-9eb1-4185-a034-84943b7fdfe9" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_407b55b4-3aef-4dd1-aa8e-3dfcaef59d14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_d8ab567f-96b6-4af1-8416-b91ae06ba38d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_fba14d14-014b-4e78-9615-9612b953312e" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_d8ab567f-96b6-4af1-8416-b91ae06ba38d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d8ab567f-96b6-4af1-8416-b91ae06ba38d_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_d8ab567f-96b6-4af1-8416-b91ae06ba38d" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_d8ab567f-96b6-4af1-8416-b91ae06ba38d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8374693b-d573-42a2-960f-747004a2626b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_d8ab567f-96b6-4af1-8416-b91ae06ba38d" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8374693b-d573-42a2-960f-747004a2626b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_4e9d142c-32d7-4591-9470-1194ba48e4f6" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8374693b-d573-42a2-960f-747004a2626b" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_4e9d142c-32d7-4591-9470-1194ba48e4f6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_ed82ff07-a723-48c1-b249-49376b15394d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_8374693b-d573-42a2-960f-747004a2626b" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_ed82ff07-a723-48c1-b249-49376b15394d" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/FairValueofFinancialInstrumentsUnrestrictedMarketableSecuritiesDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#FairValueofFinancialInstrumentsUnrestrictedMarketableSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/FairValueofFinancialInstrumentsUnrestrictedMarketableSecuritiesDetails" xlink:type="extended" id="i1c32851f3f724f9c80d72162bcee40a2_FairValueofFinancialInstrumentsUnrestrictedMarketableSecuritiesDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/FairValueofFinancialInstrumentsFairValueofFinancialInstrumentsContractualMaturitiesDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#FairValueofFinancialInstrumentsFairValueofFinancialInstrumentsContractualMaturitiesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/FairValueofFinancialInstrumentsFairValueofFinancialInstrumentsContractualMaturitiesDetails" xlink:type="extended" id="ie1e901520f7f40ac8f4f802323dab0cc_FairValueofFinancialInstrumentsFairValueofFinancialInstrumentsContractualMaturitiesDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/FairValueofFinancialInstrumentsFinancialLiabilitiesDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#FairValueofFinancialInstrumentsFinancialLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/FairValueofFinancialInstrumentsFinancialLiabilitiesDetails" xlink:type="extended" id="if8f911d93dc740c1a1756b88d3ae7896_FairValueofFinancialInstrumentsFinancialLiabilitiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7e82cd97-7f98-4f09-8feb-c5efce5651b9" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleLongTermNotesPayable_1d292b39-f41b-4381-9760-d2644058711c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConvertibleLongTermNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7e82cd97-7f98-4f09-8feb-c5efce5651b9" xlink:to="loc_us-gaap_ConvertibleLongTermNotesPayable_1d292b39-f41b-4381-9760-d2644058711c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtFairValueDisclosures_abd7707c-6179-437e-952f-4fac36d103df" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConvertibleDebtFairValueDisclosures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7e82cd97-7f98-4f09-8feb-c5efce5651b9" xlink:to="loc_us-gaap_ConvertibleDebtFairValueDisclosures_abd7707c-6179-437e-952f-4fac36d103df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2669f1bd-6cb2-4e96-8e04-2cba97c328fd" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_7e82cd97-7f98-4f09-8feb-c5efce5651b9" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2669f1bd-6cb2-4e96-8e04-2cba97c328fd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_9d77d26b-002a-44a7-8553-d538c765432e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2669f1bd-6cb2-4e96-8e04-2cba97c328fd" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_9d77d26b-002a-44a7-8553-d538c765432e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_9d77d26b-002a-44a7-8553-d538c765432e_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_9d77d26b-002a-44a7-8553-d538c765432e" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_9d77d26b-002a-44a7-8553-d538c765432e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_333fc198-b3c1-4b5e-8396-3476002f2ac4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_9d77d26b-002a-44a7-8553-d538c765432e" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_333fc198-b3c1-4b5e-8396-3476002f2ac4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleNotesPayableMember_cd72ed68-5a6f-4244-9ad0-039848951e12" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConvertibleNotesPayableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_333fc198-b3c1-4b5e-8396-3476002f2ac4" xlink:to="loc_us-gaap_ConvertibleNotesPayableMember_cd72ed68-5a6f-4244-9ad0-039848951e12" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_812a842f-1916-4d3e-830b-85e87f1d613c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_2669f1bd-6cb2-4e96-8e04-2cba97c328fd" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_812a842f-1916-4d3e-830b-85e87f1d613c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_812a842f-1916-4d3e-830b-85e87f1d613c_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_812a842f-1916-4d3e-830b-85e87f1d613c" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_812a842f-1916-4d3e-830b-85e87f1d613c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_57378fb1-edbe-4423-8837-11a31ff62e97" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_812a842f-1916-4d3e-830b-85e87f1d613c" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_57378fb1-edbe-4423-8837-11a31ff62e97" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_d20750ec-b60e-41b3-be42-1df6965630cf" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_57378fb1-edbe-4423-8837-11a31ff62e97" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_d20750ec-b60e-41b3-be42-1df6965630cf" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/ConvertibleSeniorNotesDue2023" xlink:type="simple" xlink:href="supn-20200331.xsd#ConvertibleSeniorNotesDue2023"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ConvertibleSeniorNotesDue2023" xlink:type="extended" id="ifeb145e4711944e782fa61002c6ee95f_ConvertibleSeniorNotesDue2023"/>
  <link:roleRef roleURI="http://www.supernus.com/role/ConvertibleSeniorNotesDue2023Tables" xlink:type="simple" xlink:href="supn-20200331.xsd#ConvertibleSeniorNotesDue2023Tables"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ConvertibleSeniorNotesDue2023Tables" xlink:type="extended" id="i753ec51a52354c099e5a80f0c15f3eb5_ConvertibleSeniorNotesDue2023Tables"/>
  <link:roleRef roleURI="http://www.supernus.com/role/ConvertibleSeniorNotesDue2023NarrativeDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#ConvertibleSeniorNotesDue2023NarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ConvertibleSeniorNotesDue2023NarrativeDetails" xlink:type="extended" id="i059dae19c3a644bcb35514e2ba4e83a0_ConvertibleSeniorNotesDue2023NarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_01d99d52-f69e-41f8-b156-66b244fb3087" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_ee305bb1-ae04-48be-a3d1-1e6b2df83246" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01d99d52-f69e-41f8-b156-66b244fb3087" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_ee305bb1-ae04-48be-a3d1-1e6b2df83246" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_2c8cca6d-176a-4db4-acda-684ce45a1687" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01d99d52-f69e-41f8-b156-66b244fb3087" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_2c8cca6d-176a-4db4-acda-684ce45a1687" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_0b560467-39c3-4533-86d5-48be03ce6629" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01d99d52-f69e-41f8-b156-66b244fb3087" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_0b560467-39c3-4533-86d5-48be03ce6629" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_bae21927-82a5-4800-b742-14a7ce4f9fe2" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01d99d52-f69e-41f8-b156-66b244fb3087" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_bae21927-82a5-4800-b742-14a7ce4f9fe2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_740bbaa5-80c6-477f-8c19-901d50a46e24" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01d99d52-f69e-41f8-b156-66b244fb3087" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_740bbaa5-80c6-477f-8c19-901d50a46e24" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1_e344a6f7-ec2a-4f3c-a47d-42143676aebf" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01d99d52-f69e-41f8-b156-66b244fb3087" xlink:to="loc_us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1_e344a6f7-ec2a-4f3c-a47d-42143676aebf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionConvertedInstrumentSharesIssued1_9e252f6f-5ed7-4fba-b1e7-82f985e78326" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtConversionConvertedInstrumentSharesIssued1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01d99d52-f69e-41f8-b156-66b244fb3087" xlink:to="loc_us-gaap_DebtConversionConvertedInstrumentSharesIssued1_9e252f6f-5ed7-4fba-b1e7-82f985e78326" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_99c52814-3634-4b25-b563-aaf7404ba316" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01d99d52-f69e-41f8-b156-66b244fb3087" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_99c52814-3634-4b25-b563-aaf7404ba316" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_ClassOfWarrantOrRightNumberOfSharesInWhichHolderCanBeEntitledPerWarrantsAtStrikePrice_439f78fe-9088-4e10-b6ec-913b4948f146" xlink:href="supn-20200331.xsd#supn_ClassOfWarrantOrRightNumberOfSharesInWhichHolderCanBeEntitledPerWarrantsAtStrikePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01d99d52-f69e-41f8-b156-66b244fb3087" xlink:to="loc_supn_ClassOfWarrantOrRightNumberOfSharesInWhichHolderCanBeEntitledPerWarrantsAtStrikePrice_439f78fe-9088-4e10-b6ec-913b4948f146" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_37722fe2-886b-4d45-8448-d932162e8842" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01d99d52-f69e-41f8-b156-66b244fb3087" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_37722fe2-886b-4d45-8448-d932162e8842" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtConversionOriginalDebtAmount1_6952b3c2-35b6-4ee8-ac5b-e376d80136e0" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtConversionOriginalDebtAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01d99d52-f69e-41f8-b156-66b244fb3087" xlink:to="loc_us-gaap_DebtConversionOriginalDebtAmount1_6952b3c2-35b6-4ee8-ac5b-e376d80136e0" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_11d83638-9ed9-48b1-b92a-cc27d86ef201" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_01d99d52-f69e-41f8-b156-66b244fb3087" xlink:to="loc_us-gaap_DebtInstrumentTable_11d83638-9ed9-48b1-b92a-cc27d86ef201" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_2aaf4ddc-7945-4ef1-b8ee-5a8d9547d5a6" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_11d83638-9ed9-48b1-b92a-cc27d86ef201" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_2aaf4ddc-7945-4ef1-b8ee-5a8d9547d5a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_2aaf4ddc-7945-4ef1-b8ee-5a8d9547d5a6_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_2aaf4ddc-7945-4ef1-b8ee-5a8d9547d5a6" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_2aaf4ddc-7945-4ef1-b8ee-5a8d9547d5a6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_2398df84-0396-4c08-b5c1-2365927b5f70" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_2aaf4ddc-7945-4ef1-b8ee-5a8d9547d5a6" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_2398df84-0396-4c08-b5c1-2365927b5f70" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_PercentageOf0.625ConvertibleSeniorNotesDue2023Member_2e9e5349-558d-4589-ac45-9e424d0b2308" xlink:href="supn-20200331.xsd#supn_PercentageOf0.625ConvertibleSeniorNotesDue2023Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_2398df84-0396-4c08-b5c1-2365927b5f70" xlink:to="loc_supn_PercentageOf0.625ConvertibleSeniorNotesDue2023Member_2e9e5349-558d-4589-ac45-9e424d0b2308" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/ConvertibleSeniorNotesDue2023Summaryofliabilitycomponentof2023NotesDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#ConvertibleSeniorNotesDue2023Summaryofliabilitycomponentof2023NotesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ConvertibleSeniorNotesDue2023Summaryofliabilitycomponentof2023NotesDetails" xlink:type="extended" id="if7999a542d124d02aba4e03307c668cc_ConvertibleSeniorNotesDue2023Summaryofliabilitycomponentof2023NotesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_2742f47f-2ee4-4277-a82c-fa948ddbcc4b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_fc501a67-3800-4699-848d-9a83bea1bb6b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2742f47f-2ee4-4277-a82c-fa948ddbcc4b" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_fc501a67-3800-4699-848d-9a83bea1bb6b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_8e05009f-42ff-4acd-8e6f-470c49b57786" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2742f47f-2ee4-4277-a82c-fa948ddbcc4b" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_8e05009f-42ff-4acd-8e6f-470c49b57786" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleLongTermNotesPayable_8de19f26-f3b0-47bb-ae88-2bbeddf6c5fb" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConvertibleLongTermNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2742f47f-2ee4-4277-a82c-fa948ddbcc4b" xlink:to="loc_us-gaap_ConvertibleLongTermNotesPayable_8de19f26-f3b0-47bb-ae88-2bbeddf6c5fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_0c0dc160-b1eb-4483-a1a6-ecb9c5e0f52f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_2742f47f-2ee4-4277-a82c-fa948ddbcc4b" xlink:to="loc_us-gaap_DebtInstrumentTable_0c0dc160-b1eb-4483-a1a6-ecb9c5e0f52f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_3f7a9560-7d99-4072-84f0-4e0d347f363c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_0c0dc160-b1eb-4483-a1a6-ecb9c5e0f52f" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_3f7a9560-7d99-4072-84f0-4e0d347f363c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_3f7a9560-7d99-4072-84f0-4e0d347f363c_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_3f7a9560-7d99-4072-84f0-4e0d347f363c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_3f7a9560-7d99-4072-84f0-4e0d347f363c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_bfe4390d-e7da-4462-a1c9-77ca97e33287" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_3f7a9560-7d99-4072-84f0-4e0d347f363c" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_bfe4390d-e7da-4462-a1c9-77ca97e33287" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_PercentageOf0.625ConvertibleSeniorNotesDue2023Member_176201a2-b337-4d5d-b415-dc1dbdcbd9bf" xlink:href="supn-20200331.xsd#supn_PercentageOf0.625ConvertibleSeniorNotesDue2023Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_bfe4390d-e7da-4462-a1c9-77ca97e33287" xlink:to="loc_supn_PercentageOf0.625ConvertibleSeniorNotesDue2023Member_176201a2-b337-4d5d-b415-dc1dbdcbd9bf" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/ShareBasedPayments" xlink:type="simple" xlink:href="supn-20200331.xsd#ShareBasedPayments"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ShareBasedPayments" xlink:type="extended" id="i1b8f0547673c4dbaafa759f71ef298f3_ShareBasedPayments"/>
  <link:roleRef roleURI="http://www.supernus.com/role/ShareBasedPaymentsTables" xlink:type="simple" xlink:href="supn-20200331.xsd#ShareBasedPaymentsTables"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ShareBasedPaymentsTables" xlink:type="extended" id="i07d4214010be407ca5a3dc2f38f48a71_ShareBasedPaymentsTables"/>
  <link:roleRef roleURI="http://www.supernus.com/role/ShareBasedPaymentsSharebasedCompensationExpenseDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#ShareBasedPaymentsSharebasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ShareBasedPaymentsSharebasedCompensationExpenseDetails" xlink:type="extended" id="ibb13a39770f047198ae058964e910570_ShareBasedPaymentsSharebasedCompensationExpenseDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_3470f2e2-d1f3-4073-8a6f-bc167ff4b557" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_ccd592d6-7934-4878-8e50-c1d630fcbea5" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_3470f2e2-d1f3-4073-8a6f-bc167ff4b557" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_ccd592d6-7934-4878-8e50-c1d630fcbea5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_10a13f63-faf6-4367-a39f-df3a26bd1402" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_3470f2e2-d1f3-4073-8a6f-bc167ff4b557" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_10a13f63-faf6-4367-a39f-df3a26bd1402" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_a0dd7d3a-d9fd-4af4-8f12-eec5b844b510" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_10a13f63-faf6-4367-a39f-df3a26bd1402" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_a0dd7d3a-d9fd-4af4-8f12-eec5b844b510" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_a0dd7d3a-d9fd-4af4-8f12-eec5b844b510_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_a0dd7d3a-d9fd-4af4-8f12-eec5b844b510" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_a0dd7d3a-d9fd-4af4-8f12-eec5b844b510_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_720f0dc7-3a7c-414e-bbb1-91ebee1512d0" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_a0dd7d3a-d9fd-4af4-8f12-eec5b844b510" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_720f0dc7-3a7c-414e-bbb1-91ebee1512d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_1cb657cb-6e1e-4412-85dd-397174205f3c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_720f0dc7-3a7c-414e-bbb1-91ebee1512d0" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_1cb657cb-6e1e-4412-85dd-397174205f3c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_bd156d00-2607-4a59-9693-ef978c674fdb" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_720f0dc7-3a7c-414e-bbb1-91ebee1512d0" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_bd156d00-2607-4a59-9693-ef978c674fdb" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/ShareBasedPaymentsActivityDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#ShareBasedPaymentsActivityDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ShareBasedPaymentsActivityDetails" xlink:type="extended" id="i7c0c3af7d7d64ba3a9d9514ae99f5a08_ShareBasedPaymentsActivityDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2caa345e-aa49-4c9a-b53c-a5995abf4ee4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_f402fd41-6106-46a5-9a16-f38d568e0cf7" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2caa345e-aa49-4c9a-b53c-a5995abf4ee4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_f402fd41-6106-46a5-9a16-f38d568e0cf7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_451a623b-4a26-4c75-b11f-8c4f3fe8f0a6" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_f402fd41-6106-46a5-9a16-f38d568e0cf7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_451a623b-4a26-4c75-b11f-8c4f3fe8f0a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_c6f251fa-6daf-4cdf-9274-8faf95f8fb6b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_f402fd41-6106-46a5-9a16-f38d568e0cf7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_c6f251fa-6daf-4cdf-9274-8faf95f8fb6b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_0a25d3d4-c378-416c-900a-03d8fffbb1ff" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_f402fd41-6106-46a5-9a16-f38d568e0cf7" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_0a25d3d4-c378-416c-900a-03d8fffbb1ff" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_17f7ed4b-e564-4036-ae1b-2173c1152e34" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_f402fd41-6106-46a5-9a16-f38d568e0cf7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_17f7ed4b-e564-4036-ae1b-2173c1152e34" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_8b22ea7e-f230-490d-bbe6-119cf247764e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_7b37e8c4-4ac9-436a-92a6-072fd0fabb3f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_f402fd41-6106-46a5-9a16-f38d568e0cf7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingNumber_7b37e8c4-4ac9-436a-92a6-072fd0fabb3f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_bb0b88a4-f8f6-48f1-82d0-9dcf9ee21dd3" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_f402fd41-6106-46a5-9a16-f38d568e0cf7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_bb0b88a4-f8f6-48f1-82d0-9dcf9ee21dd3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_b2cf220a-ded5-4f62-b6f7-4d0a7627761f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2caa345e-aa49-4c9a-b53c-a5995abf4ee4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_b2cf220a-ded5-4f62-b6f7-4d0a7627761f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_4b116b9c-5968-48b5-81fa-1e3550b653eb" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_b2cf220a-ded5-4f62-b6f7-4d0a7627761f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_4b116b9c-5968-48b5-81fa-1e3550b653eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_75e707d5-bfe4-4963-9684-46db39d765b4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_b2cf220a-ded5-4f62-b6f7-4d0a7627761f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_75e707d5-bfe4-4963-9684-46db39d765b4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_b998de27-e049-4dcb-b136-0e728b9d28b7" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_b2cf220a-ded5-4f62-b6f7-4d0a7627761f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_b998de27-e049-4dcb-b136-0e728b9d28b7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_151096b5-ead3-4596-a499-8b2f523ec7c5" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_b2cf220a-ded5-4f62-b6f7-4d0a7627761f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_151096b5-ead3-4596-a499-8b2f523ec7c5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_ca710f89-650b-4987-8c5e-ac08e37f9515" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_6ce24fb4-3651-42f2-8a5e-22ccd870a4d2" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_b2cf220a-ded5-4f62-b6f7-4d0a7627761f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageExercisePrice_6ce24fb4-3651-42f2-8a5e-22ccd870a4d2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_2fc33b01-8925-402e-9203-688a6460c099" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_b2cf220a-ded5-4f62-b6f7-4d0a7627761f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_2fc33b01-8925-402e-9203-688a6460c099" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_e83b6171-5f21-4fbf-87d7-38eafa785ce5" xlink:href="supn-20200331.xsd#supn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2caa345e-aa49-4c9a-b53c-a5995abf4ee4" xlink:to="loc_supn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_e83b6171-5f21-4fbf-87d7-38eafa785ce5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_8831a734-185a-428b-9ac1-20dd42abe142" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_supn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_e83b6171-5f21-4fbf-87d7-38eafa785ce5" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_8831a734-185a-428b-9ac1-20dd42abe142" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_e1482e65-298f-4d5e-a7b2-984315cf7d78" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_supn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_e83b6171-5f21-4fbf-87d7-38eafa785ce5" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedAndExpectedToVestOutstandingWeightedAverageRemainingContractualTerm1_e1482e65-298f-4d5e-a7b2-984315cf7d78" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_9da74d4e-5911-4d2f-9a6f-0f1e893abac1" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_supn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsWeightedAverageRemainingContractualTermAbstract_e83b6171-5f21-4fbf-87d7-38eafa785ce5" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1_9da74d4e-5911-4d2f-9a6f-0f1e893abac1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_6289a025-c6d5-44d7-afca-9a95b4623551" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_2caa345e-aa49-4c9a-b53c-a5995abf4ee4" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_6289a025-c6d5-44d7-afca-9a95b4623551" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_ca9284c2-061f-4f76-94ae-e4687c4ecb7d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_6289a025-c6d5-44d7-afca-9a95b4623551" xlink:to="loc_us-gaap_AwardTypeAxis_ca9284c2-061f-4f76-94ae-e4687c4ecb7d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ca9284c2-061f-4f76-94ae-e4687c4ecb7d_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_ca9284c2-061f-4f76-94ae-e4687c4ecb7d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ca9284c2-061f-4f76-94ae-e4687c4ecb7d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_82411178-1da8-40ce-8041-d1235e801ae0" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_ca9284c2-061f-4f76-94ae-e4687c4ecb7d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_82411178-1da8-40ce-8041-d1235e801ae0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_StockOptionStockAppreciationRightsMember_e8c6335e-3adc-4de3-aea9-ce5cec2d30b6" xlink:href="supn-20200331.xsd#supn_StockOptionStockAppreciationRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_82411178-1da8-40ce-8041-d1235e801ae0" xlink:to="loc_supn_StockOptionStockAppreciationRightsMember_e8c6335e-3adc-4de3-aea9-ce5cec2d30b6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/ShareBasedPaymentsNarrativeDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#ShareBasedPaymentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/ShareBasedPaymentsNarrativeDetails" xlink:type="extended" id="i98a59733ea40494a8ea745dafe8772e8_ShareBasedPaymentsNarrativeDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_908ca70f-4452-41ee-956d-fa3c2f3781a8" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_803af4f0-bfe8-49d0-aa1a-bac1899ee487" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_908ca70f-4452-41ee-956d-fa3c2f3781a8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_803af4f0-bfe8-49d0-aa1a-bac1899ee487" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_a5f6f842-d6ab-4e70-b2ba-8e8e437e64e5" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_908ca70f-4452-41ee-956d-fa3c2f3781a8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_a5f6f842-d6ab-4e70-b2ba-8e8e437e64e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_4109f725-0c90-4ae7-9fb6-56cda31ab4fe" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_908ca70f-4452-41ee-956d-fa3c2f3781a8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_4109f725-0c90-4ae7-9fb6-56cda31ab4fe" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_d01be63b-0c19-4fb6-8758-5c64cc26be8f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_908ca70f-4452-41ee-956d-fa3c2f3781a8" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_d01be63b-0c19-4fb6-8758-5c64cc26be8f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_58a98047-75ad-4ad9-9198-0c9ca1348ff3" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_908ca70f-4452-41ee-956d-fa3c2f3781a8" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_58a98047-75ad-4ad9-9198-0c9ca1348ff3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_3dc76560-0b1e-41bf-bfb2-2477a475a01b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_58a98047-75ad-4ad9-9198-0c9ca1348ff3" xlink:to="loc_us-gaap_AwardTypeAxis_3dc76560-0b1e-41bf-bfb2-2477a475a01b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3dc76560-0b1e-41bf-bfb2-2477a475a01b_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_3dc76560-0b1e-41bf-bfb2-2477a475a01b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3dc76560-0b1e-41bf-bfb2-2477a475a01b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_09c6ff7d-f18a-401f-be80-1e581de2341d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_3dc76560-0b1e-41bf-bfb2-2477a475a01b" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_09c6ff7d-f18a-401f-be80-1e581de2341d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_e06f0bed-f4ff-4f14-afff-eee0ef98bb19" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_09c6ff7d-f18a-401f-be80-1e581de2341d" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_e06f0bed-f4ff-4f14-afff-eee0ef98bb19" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_ffa3f4bf-ac9e-4ddd-ab1c-a7b60b7498c9" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_09c6ff7d-f18a-401f-be80-1e581de2341d" xlink:to="loc_us-gaap_PerformanceSharesMember_ffa3f4bf-ac9e-4ddd-ab1c-a7b60b7498c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_MarketBasedPerformanceSharesMember_7a043a38-fef4-4882-ad37-c47553e0a343" xlink:href="supn-20200331.xsd#supn_MarketBasedPerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_09c6ff7d-f18a-401f-be80-1e581de2341d" xlink:to="loc_supn_MarketBasedPerformanceSharesMember_7a043a38-fef4-4882-ad37-c47553e0a343" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/EarningsperShare" xlink:type="simple" xlink:href="supn-20200331.xsd#EarningsperShare"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/EarningsperShare" xlink:type="extended" id="ic6b3c973ba6240758ccf06b07c38391e_EarningsperShare"/>
  <link:roleRef roleURI="http://www.supernus.com/role/EarningsperShareTables" xlink:type="simple" xlink:href="supn-20200331.xsd#EarningsperShareTables"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/EarningsperShareTables" xlink:type="extended" id="iaecebd8221a7439e843208fc03dcb13c_EarningsperShareTables"/>
  <link:roleRef roleURI="http://www.supernus.com/role/EarningsperShareDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#EarningsperShareDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/EarningsperShareDetails" xlink:type="extended" id="i7c98cb520cb042ac8e422f751cbfe954_EarningsperShareDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e5af578b-f54d-413e-b0a2-45b2ba746e8a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_78a80b19-215e-4264-9d09-d9a269089067" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e5af578b-f54d-413e-b0a2-45b2ba746e8a" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_78a80b19-215e-4264-9d09-d9a269089067" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_bd9e5e97-e81e-44f0-9330-ba8356a3de54" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e5af578b-f54d-413e-b0a2-45b2ba746e8a" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_bd9e5e97-e81e-44f0-9330-ba8356a3de54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_492d84ad-6a2e-4a30-82b1-7715a3e27887" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e5af578b-f54d-413e-b0a2-45b2ba746e8a" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_492d84ad-6a2e-4a30-82b1-7715a3e27887" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_3c5063ef-cf56-4385-8a40-c63d7df7d15e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e5af578b-f54d-413e-b0a2-45b2ba746e8a" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_3c5063ef-cf56-4385-8a40-c63d7df7d15e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_add2944c-c585-495b-8b8c-8c43a9eb9223" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_3c5063ef-cf56-4385-8a40-c63d7df7d15e" xlink:to="loc_us-gaap_NetIncomeLoss_add2944c-c585-495b-8b8c-8c43a9eb9223" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_bcd38785-c161-4ece-8ed5-9cc5512884c8" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e5af578b-f54d-413e-b0a2-45b2ba746e8a" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_bcd38785-c161-4ece-8ed5-9cc5512884c8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_4bc4bddf-db17-4cb2-914c-e927285d86b6" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_bcd38785-c161-4ece-8ed5-9cc5512884c8" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_4bc4bddf-db17-4cb2-914c-e927285d86b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_d5cbe8b0-44a9-4fb0-87d2-da4e2116e928" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_bcd38785-c161-4ece-8ed5-9cc5512884c8" xlink:to="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_d5cbe8b0-44a9-4fb0-87d2-da4e2116e928" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_c05e5016-5d01-4e35-8e89-4abee058b333" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_d5cbe8b0-44a9-4fb0-87d2-da4e2116e928" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_c05e5016-5d01-4e35-8e89-4abee058b333" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_d173aba1-dc4f-4993-98b4-ae07c86b3c7b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasicAbstract_bcd38785-c161-4ece-8ed5-9cc5512884c8" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_d173aba1-dc4f-4993-98b4-ae07c86b3c7b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_bc497b8e-b21c-42f3-a4f7-8a50e59e24be" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e5af578b-f54d-413e-b0a2-45b2ba746e8a" xlink:to="loc_us-gaap_EarningsPerShareBasic_bc497b8e-b21c-42f3-a4f7-8a50e59e24be" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_e33bc60b-e8f5-4030-aa34-fff8762250dc" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e5af578b-f54d-413e-b0a2-45b2ba746e8a" xlink:to="loc_us-gaap_EarningsPerShareDiluted_e33bc60b-e8f5-4030-aa34-fff8762250dc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_a8d85aaa-5c67-4400-bf6d-1a11bcd66cb2" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_e5af578b-f54d-413e-b0a2-45b2ba746e8a" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_a8d85aaa-5c67-4400-bf6d-1a11bcd66cb2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_6300cc89-8797-4178-b106-9465b55bfb5e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_a8d85aaa-5c67-4400-bf6d-1a11bcd66cb2" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_6300cc89-8797-4178-b106-9465b55bfb5e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_6300cc89-8797-4178-b106-9465b55bfb5e_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_6300cc89-8797-4178-b106-9465b55bfb5e" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_6300cc89-8797-4178-b106-9465b55bfb5e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_60965ff0-d7c5-45b6-bb59-5ab827a4762d" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_6300cc89-8797-4178-b106-9465b55bfb5e" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_60965ff0-d7c5-45b6-bb59-5ab827a4762d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_PercentageOf0.625ConvertibleSeniorNotesDue2023Member_98965905-209b-40f0-aae1-8e404b002cc7" xlink:href="supn-20200331.xsd#supn_PercentageOf0.625ConvertibleSeniorNotesDue2023Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_60965ff0-d7c5-45b6-bb59-5ab827a4762d" xlink:to="loc_supn_PercentageOf0.625ConvertibleSeniorNotesDue2023Member_98965905-209b-40f0-aae1-8e404b002cc7" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/IncomeTaxes" xlink:type="simple" xlink:href="supn-20200331.xsd#IncomeTaxes"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/IncomeTaxes" xlink:type="extended" id="icdda8adcc84449a3802f19798e50ad73_IncomeTaxes"/>
  <link:roleRef roleURI="http://www.supernus.com/role/IncomeTaxesTables" xlink:type="simple" xlink:href="supn-20200331.xsd#IncomeTaxesTables"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/IncomeTaxesTables" xlink:type="extended" id="ie13c68df97ca4cdfb3e18e27a8325c9c_IncomeTaxesTables"/>
  <link:roleRef roleURI="http://www.supernus.com/role/IncomeTaxesDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#IncomeTaxesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/IncomeTaxesDetails" xlink:type="extended" id="i51b594e9e4764e3c8665a03d1f104c96_IncomeTaxesDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/Leases" xlink:type="simple" xlink:href="supn-20200331.xsd#Leases"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/Leases" xlink:type="extended" id="i60bd3a0c40464551999bf6c4c63777f6_Leases"/>
  <link:roleRef roleURI="http://www.supernus.com/role/LeasesTables" xlink:type="simple" xlink:href="supn-20200331.xsd#LeasesTables"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/LeasesTables" xlink:type="extended" id="i8cb047c2c9ed49e3a542b582cd00146a_LeasesTables"/>
  <link:roleRef roleURI="http://www.supernus.com/role/LeasesNewHeadquartersLeaseDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#LeasesNewHeadquartersLeaseDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/LeasesNewHeadquartersLeaseDetails" xlink:type="extended" id="i890fe71c855b448fb4e7b400a580e84a_LeasesNewHeadquartersLeaseDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_2e6b6345-856b-457c-a25c-0d9f40ff662b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_4d04207a-33a1-4a1d-9f6c-b7075c59f7c4" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_2e6b6345-856b-457c-a25c-0d9f40ff662b" xlink:to="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_4d04207a-33a1-4a1d-9f6c-b7075c59f7c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_OperatingLeasesRentalExpensesInitialFixedMonthlyRentalPayments_0035b6e8-936b-4fa1-b0fb-533936a00e81" xlink:href="supn-20200331.xsd#supn_OperatingLeasesRentalExpensesInitialFixedMonthlyRentalPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_2e6b6345-856b-457c-a25c-0d9f40ff662b" xlink:to="loc_supn_OperatingLeasesRentalExpensesInitialFixedMonthlyRentalPayments_0035b6e8-936b-4fa1-b0fb-533936a00e81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_OperatingLeasesRentalExpensesAnnualIncreaseInRentalPaymentsPercentage_e6efe345-8e3c-4191-a469-008d57fd0ad1" xlink:href="supn-20200331.xsd#supn_OperatingLeasesRentalExpensesAnnualIncreaseInRentalPaymentsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_2e6b6345-856b-457c-a25c-0d9f40ff662b" xlink:to="loc_supn_OperatingLeasesRentalExpensesAnnualIncreaseInRentalPaymentsPercentage_e6efe345-8e3c-4191-a469-008d57fd0ad1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecurityDeposit_3f772e28-78a4-4d89-b4a6-5639fa87921f" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SecurityDeposit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_2e6b6345-856b-457c-a25c-0d9f40ff662b" xlink:to="loc_us-gaap_SecurityDeposit_3f772e28-78a4-4d89-b4a6-5639fa87921f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_OperatingLeasesAdditionalAllowanceForTenantAndCapitalImprovement_45f78969-c034-41a8-a400-44db448f482f" xlink:href="supn-20200331.xsd#supn_OperatingLeasesAdditionalAllowanceForTenantAndCapitalImprovement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_2e6b6345-856b-457c-a25c-0d9f40ff662b" xlink:to="loc_supn_OperatingLeasesAdditionalAllowanceForTenantAndCapitalImprovement_45f78969-c034-41a8-a400-44db448f482f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_beb25512-7476-4f05-b2ce-46d3d798789a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_2e6b6345-856b-457c-a25c-0d9f40ff662b" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_beb25512-7476-4f05-b2ce-46d3d798789a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_16481761-8f3d-45cb-b24d-4e4b58e96d4d" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_beb25512-7476-4f05-b2ce-46d3d798789a" xlink:to="loc_srt_CounterpartyNameAxis_16481761-8f3d-45cb-b24d-4e4b58e96d4d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_16481761-8f3d-45cb-b24d-4e4b58e96d4d_default" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_16481761-8f3d-45cb-b24d-4e4b58e96d4d" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_16481761-8f3d-45cb-b24d-4e4b58e96d4d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_e7609651-bb86-4515-84f7-cba8f5b66d6f" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_16481761-8f3d-45cb-b24d-4e4b58e96d4d" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_e7609651-bb86-4515-84f7-cba8f5b66d6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_AdventKeyWestLlcMember_1f80a64c-0da8-4e79-a15f-1ca6f0eedd01" xlink:href="supn-20200331.xsd#supn_AdventKeyWestLlcMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_e7609651-bb86-4515-84f7-cba8f5b66d6f" xlink:to="loc_supn_AdventKeyWestLlcMember_1f80a64c-0da8-4e79-a15f-1ca6f0eedd01" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/LeasesLeasesBalanceSheetInformationDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#LeasesLeasesBalanceSheetInformationDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/LeasesLeasesBalanceSheetInformationDetails" xlink:type="extended" id="i303d6ec15be94c70a94b9408978672a1_LeasesLeasesBalanceSheetInformationDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/LeasesLeaseCostsDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#LeasesLeaseCostsDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/LeasesLeaseCostsDetails" xlink:type="extended" id="ifb0e6c61d1634041b275af3184554a15_LeasesLeaseCostsDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/LeasesSupplementalCashFlowsDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#LeasesSupplementalCashFlowsDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/LeasesSupplementalCashFlowsDetails" xlink:type="extended" id="i7c21156a3a594cd5bc146c87f8d8035a_LeasesSupplementalCashFlowsDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/LeasesScheduleofMaturitiesofLeaseLiabilitiesDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#LeasesScheduleofMaturitiesofLeaseLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/LeasesScheduleofMaturitiesofLeaseLiabilitiesDetails" xlink:type="extended" id="i697e76843aca4dcb943f3cca1c4a91b2_LeasesScheduleofMaturitiesofLeaseLiabilitiesDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/AccountsReceivable" xlink:type="simple" xlink:href="supn-20200331.xsd#AccountsReceivable"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/AccountsReceivable" xlink:type="extended" id="ie768013e98be44fa9c1380c207309571_AccountsReceivable"/>
  <link:roleRef roleURI="http://www.supernus.com/role/AccountsReceivableDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#AccountsReceivableDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/AccountsReceivableDetails" xlink:type="extended" id="icb14ef5ba0bb4ca2b3a71ea2891de5db_AccountsReceivableDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/Inventories" xlink:type="simple" xlink:href="supn-20200331.xsd#Inventories"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/Inventories" xlink:type="extended" id="i9dcac88d76324621909f5bd61fc6b34f_Inventories"/>
  <link:roleRef roleURI="http://www.supernus.com/role/InventoriesTables" xlink:type="simple" xlink:href="supn-20200331.xsd#InventoriesTables"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/InventoriesTables" xlink:type="extended" id="i47ad178288294da396b625144d8f3357_InventoriesTables"/>
  <link:roleRef roleURI="http://www.supernus.com/role/InventoriesDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#InventoriesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/InventoriesDetails" xlink:type="extended" id="i468e7581c7b24beda40d210f07ff1054_InventoriesDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/PropertyandEquipment" xlink:type="simple" xlink:href="supn-20200331.xsd#PropertyandEquipment"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/PropertyandEquipment" xlink:type="extended" id="i0aa33d315ea54a7992eed5d8ba8c88ad_PropertyandEquipment"/>
  <link:roleRef roleURI="http://www.supernus.com/role/PropertyandEquipmentTables" xlink:type="simple" xlink:href="supn-20200331.xsd#PropertyandEquipmentTables"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/PropertyandEquipmentTables" xlink:type="extended" id="i1a2f6c6259794fccb364b47a9bc5586b_PropertyandEquipmentTables"/>
  <link:roleRef roleURI="http://www.supernus.com/role/PropertyandEquipmentDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#PropertyandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/PropertyandEquipmentDetails" xlink:type="extended" id="ia150a6ef2a4a49b699ff549f127ef707_PropertyandEquipmentDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_4c075cee-6c0d-422a-8de9-bc62051c8563" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_ab60a0f9-2e2a-416e-8b81-46d57eb4d698" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_4c075cee-6c0d-422a-8de9-bc62051c8563" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_ab60a0f9-2e2a-416e-8b81-46d57eb4d698" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_0ec6fa07-a05b-4c94-9a2d-04366b69c713" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_4c075cee-6c0d-422a-8de9-bc62051c8563" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_0ec6fa07-a05b-4c94-9a2d-04366b69c713" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_b565b1e7-ec07-4491-9bde-8f49f7dc2fff" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_4c075cee-6c0d-422a-8de9-bc62051c8563" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_b565b1e7-ec07-4491-9bde-8f49f7dc2fff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_c6b6d4c7-d89b-4cfc-a2bc-bb1bb8a73fb8" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_4c075cee-6c0d-422a-8de9-bc62051c8563" xlink:to="loc_us-gaap_DepreciationAndAmortization_c6b6d4c7-d89b-4cfc-a2bc-bb1bb8a73fb8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_a834f856-7425-4f76-83de-e54c5ff62597" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_4c075cee-6c0d-422a-8de9-bc62051c8563" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_a834f856-7425-4f76-83de-e54c5ff62597" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_3dbc8cda-bf41-4e74-8dfd-a55bc1f95ca1" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_a834f856-7425-4f76-83de-e54c5ff62597" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_3dbc8cda-bf41-4e74-8dfd-a55bc1f95ca1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_3dbc8cda-bf41-4e74-8dfd-a55bc1f95ca1_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_3dbc8cda-bf41-4e74-8dfd-a55bc1f95ca1" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_3dbc8cda-bf41-4e74-8dfd-a55bc1f95ca1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_54d7ad52-0608-45fd-933b-ed0c6dd6b564" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_3dbc8cda-bf41-4e74-8dfd-a55bc1f95ca1" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_54d7ad52-0608-45fd-933b-ed0c6dd6b564" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_LabEquipmentAndFurnitureMember_07fba9a9-971b-4d17-a8a6-76bfa8f5e1fa" xlink:href="supn-20200331.xsd#supn_LabEquipmentAndFurnitureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_54d7ad52-0608-45fd-933b-ed0c6dd6b564" xlink:to="loc_supn_LabEquipmentAndFurnitureMember_07fba9a9-971b-4d17-a8a6-76bfa8f5e1fa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_15fbc865-63fe-49fa-88ba-a1509b05a2b3" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_54d7ad52-0608-45fd-933b-ed0c6dd6b564" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_15fbc865-63fe-49fa-88ba-a1509b05a2b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_6b2339e7-a783-46ba-a49f-dc4a5dad269c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ComputerSoftwareIntangibleAssetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_54d7ad52-0608-45fd-933b-ed0c6dd6b564" xlink:to="loc_us-gaap_ComputerSoftwareIntangibleAssetMember_6b2339e7-a783-46ba-a49f-dc4a5dad269c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_132ed606-5f35-40a4-ad90-8234c4c108bd" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_54d7ad52-0608-45fd-933b-ed0c6dd6b564" xlink:to="loc_us-gaap_ComputerEquipmentMember_132ed606-5f35-40a4-ad90-8234c4c108bd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_80247bc9-5c0f-4c86-9ea1-5cfd64791ac2" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_54d7ad52-0608-45fd-933b-ed0c6dd6b564" xlink:to="loc_us-gaap_ConstructionInProgressMember_80247bc9-5c0f-4c86-9ea1-5cfd64791ac2" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/IntangibleAssets" xlink:type="simple" xlink:href="supn-20200331.xsd#IntangibleAssets"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/IntangibleAssets" xlink:type="extended" id="i19e47ef007654932851c66fefdb08984_IntangibleAssets"/>
  <link:roleRef roleURI="http://www.supernus.com/role/IntangibleAssetsTables" xlink:type="simple" xlink:href="supn-20200331.xsd#IntangibleAssetsTables"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/IntangibleAssetsTables" xlink:type="extended" id="ie90b9c238c57458a888c102a8a8acb7e_IntangibleAssetsTables"/>
  <link:roleRef roleURI="http://www.supernus.com/role/IntangibleAssetsDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#IntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/IntangibleAssetsDetails" xlink:type="extended" id="i60c7b92363d6422489fcf36efb1bf62f_IntangibleAssetsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_3f99b527-37a2-4db2-bfcc-599112016c32" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_003663e0-893c-4e34-82dc-3a32ec6a343b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_3f99b527-37a2-4db2-bfcc-599112016c32" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_003663e0-893c-4e34-82dc-3a32ec6a343b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_a859f884-e2a7-4bea-afee-78e0dd577a00" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_3f99b527-37a2-4db2-bfcc-599112016c32" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_a859f884-e2a7-4bea-afee-78e0dd577a00" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_8e077891-42c8-44b4-af5b-98b404cbe32b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_3f99b527-37a2-4db2-bfcc-599112016c32" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_8e077891-42c8-44b4-af5b-98b404cbe32b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_451db500-4b53-4f04-b635-8484511f7f08" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_3f99b527-37a2-4db2-bfcc-599112016c32" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_451db500-4b53-4f04-b635-8484511f7f08" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract_56e6fa11-5b4b-4e17-8144-8c9de63f71b1" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_3f99b527-37a2-4db2-bfcc-599112016c32" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract_56e6fa11-5b4b-4e17-8144-8c9de63f71b1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_0116ebee-f991-42e1-aa54-e4c3e67f43cc" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IntangibleAssetsNetExcludingGoodwillAbstract_56e6fa11-5b4b-4e17-8144-8c9de63f71b1" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_0116ebee-f991-42e1-aa54-e4c3e67f43cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_84c7c9c0-37cf-43f2-925a-a72cd5f49113" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_3f99b527-37a2-4db2-bfcc-599112016c32" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_84c7c9c0-37cf-43f2-925a-a72cd5f49113" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_79d9b64f-6d5f-445b-b136-1d0f6f84fad7" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_84c7c9c0-37cf-43f2-925a-a72cd5f49113" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_79d9b64f-6d5f-445b-b136-1d0f6f84fad7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_79d9b64f-6d5f-445b-b136-1d0f6f84fad7_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_79d9b64f-6d5f-445b-b136-1d0f6f84fad7" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_79d9b64f-6d5f-445b-b136-1d0f6f84fad7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6de96b0a-e64a-4238-9890-c47f13113433" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_79d9b64f-6d5f-445b-b136-1d0f6f84fad7" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6de96b0a-e64a-4238-9890-c47f13113433" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_PatentDefenseCostsMember_85427ef1-dc3f-484d-8a4d-92767ac145b0" xlink:href="supn-20200331.xsd#supn_PatentDefenseCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_6de96b0a-e64a-4238-9890-c47f13113433" xlink:to="loc_supn_PatentDefenseCostsMember_85427ef1-dc3f-484d-8a4d-92767ac145b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_7d412b03-2d35-4d0b-a8c6-b49cd28c29a0" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_84c7c9c0-37cf-43f2-925a-a72cd5f49113" xlink:to="loc_srt_RangeAxis_7d412b03-2d35-4d0b-a8c6-b49cd28c29a0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_7d412b03-2d35-4d0b-a8c6-b49cd28c29a0_default" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_7d412b03-2d35-4d0b-a8c6-b49cd28c29a0" xlink:to="loc_srt_RangeMember_7d412b03-2d35-4d0b-a8c6-b49cd28c29a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_087e280e-fa73-4b62-b840-a75a5c21e244" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_7d412b03-2d35-4d0b-a8c6-b49cd28c29a0" xlink:to="loc_srt_RangeMember_087e280e-fa73-4b62-b840-a75a5c21e244" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_8c1c5d59-2fdf-4cec-8d85-34ba8c057a22" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_087e280e-fa73-4b62-b840-a75a5c21e244" xlink:to="loc_srt_MinimumMember_8c1c5d59-2fdf-4cec-8d85-34ba8c057a22" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_e4dac0b2-3a23-4f52-8a1c-ed5fbda48c9e" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_087e280e-fa73-4b62-b840-a75a5c21e244" xlink:to="loc_srt_MaximumMember_e4dac0b2-3a23-4f52-8a1c-ed5fbda48c9e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.supernus.com/role/AccruedExpensesandOtherCurrentLiabilities" xlink:type="simple" xlink:href="supn-20200331.xsd#AccruedExpensesandOtherCurrentLiabilities"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/AccruedExpensesandOtherCurrentLiabilities" xlink:type="extended" id="ie038fa254ef549479a21b850d08c6c02_AccruedExpensesandOtherCurrentLiabilities"/>
  <link:roleRef roleURI="http://www.supernus.com/role/AccruedExpensesandOtherCurrentLiabilitiesTables" xlink:type="simple" xlink:href="supn-20200331.xsd#AccruedExpensesandOtherCurrentLiabilitiesTables"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/AccruedExpensesandOtherCurrentLiabilitiesTables" xlink:type="extended" id="i57670ef8bb7b44fc95fd5a2a9fa9224e_AccruedExpensesandOtherCurrentLiabilitiesTables"/>
  <link:roleRef roleURI="http://www.supernus.com/role/AccruedExpensesandOtherCurrentLiabilitiesDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#AccruedExpensesandOtherCurrentLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/AccruedExpensesandOtherCurrentLiabilitiesDetails" xlink:type="extended" id="ic6ede7fa07034570bea627734a3a689d_AccruedExpensesandOtherCurrentLiabilitiesDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/AccruedProductReturnsandRebates" xlink:type="simple" xlink:href="supn-20200331.xsd#AccruedProductReturnsandRebates"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/AccruedProductReturnsandRebates" xlink:type="extended" id="i810b852f02424e6a918801a60b43016a_AccruedProductReturnsandRebates"/>
  <link:roleRef roleURI="http://www.supernus.com/role/AccruedProductReturnsandRebatesTables" xlink:type="simple" xlink:href="supn-20200331.xsd#AccruedProductReturnsandRebatesTables"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/AccruedProductReturnsandRebatesTables" xlink:type="extended" id="i209f2c024a8947bc8023e3aac4817cd6_AccruedProductReturnsandRebatesTables"/>
  <link:roleRef roleURI="http://www.supernus.com/role/AccruedProductReturnsandRebatesDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#AccruedProductReturnsandRebatesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/AccruedProductReturnsandRebatesDetails" xlink:type="extended" id="i703e8129a8e841f8b2e85b7fcf12cc1c_AccruedProductReturnsandRebatesDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/OtherIncomeExpense" xlink:type="simple" xlink:href="supn-20200331.xsd#OtherIncomeExpense"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/OtherIncomeExpense" xlink:type="extended" id="i3d10d23b487d4e63aea6850ee686847d_OtherIncomeExpense"/>
  <link:roleRef roleURI="http://www.supernus.com/role/OtherIncomeExpenseTables" xlink:type="simple" xlink:href="supn-20200331.xsd#OtherIncomeExpenseTables"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/OtherIncomeExpenseTables" xlink:type="extended" id="i6bb5492983174404a695f564a4dffee1_OtherIncomeExpenseTables"/>
  <link:roleRef roleURI="http://www.supernus.com/role/OtherIncomeExpenseDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#OtherIncomeExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/OtherIncomeExpenseDetails" xlink:type="extended" id="ibc1bf6b8c04544179e0ce743aac32043_OtherIncomeExpenseDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/CommitmentsandContingencies" xlink:type="simple" xlink:href="supn-20200331.xsd#CommitmentsandContingencies"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CommitmentsandContingencies" xlink:type="extended" id="ib8722bda89c04a32aac8569df86ac772_CommitmentsandContingencies"/>
  <link:roleRef roleURI="http://www.supernus.com/role/CommitmentsandContingenciesDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#CommitmentsandContingenciesDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/CommitmentsandContingenciesDetails" xlink:type="extended" id="iec50d0c3845a4ea89820751047c9051b_CommitmentsandContingenciesDetails"/>
  <link:roleRef roleURI="http://www.supernus.com/role/SubsequentEvents" xlink:type="simple" xlink:href="supn-20200331.xsd#SubsequentEvents"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/SubsequentEvents" xlink:type="extended" id="ifbf5d4f69adc45b09d2b78fbf098cfdc_SubsequentEvents"/>
  <link:roleRef roleURI="http://www.supernus.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="supn-20200331.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://www.supernus.com/role/SubsequentEventsDetails" xlink:type="extended" id="i3cdf35e58a4e495f876f25ac89031586_SubsequentEventsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_88b48998-4d79-47c8-babf-d0ba7c70f547" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries_a0d10974-2186-40c9-b00b-6e786f22695a" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_88b48998-4d79-47c8-babf-d0ba7c70f547" xlink:to="loc_us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries_a0d10974-2186-40c9-b00b-6e786f22695a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_54b6d857-a7f4-4c94-aeea-8c9d9adead22" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_88b48998-4d79-47c8-babf-d0ba7c70f547" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners_54b6d857-a7f4-4c94-aeea-8c9d9adead22" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_CollaborativeArrangementPaymentForOptionIssueFee_4b819aa7-3787-4272-a8a5-91f11f67df36" xlink:href="supn-20200331.xsd#supn_CollaborativeArrangementPaymentForOptionIssueFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_88b48998-4d79-47c8-babf-d0ba7c70f547" xlink:to="loc_supn_CollaborativeArrangementPaymentForOptionIssueFee_4b819aa7-3787-4272-a8a5-91f11f67df36" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_CollaborativeArrangementPotentialPayments_38cf5543-03aa-4fd4-b3e2-b9eaf9cc87c9" xlink:href="supn-20200331.xsd#supn_CollaborativeArrangementPotentialPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_88b48998-4d79-47c8-babf-d0ba7c70f547" xlink:to="loc_supn_CollaborativeArrangementPotentialPayments_38cf5543-03aa-4fd4-b3e2-b9eaf9cc87c9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_CollaborativeArrangementUpfrontCashPayments_2789f33a-a382-422f-a7f1-c6cece49ab25" xlink:href="supn-20200331.xsd#supn_CollaborativeArrangementUpfrontCashPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_88b48998-4d79-47c8-babf-d0ba7c70f547" xlink:to="loc_supn_CollaborativeArrangementUpfrontCashPayments_2789f33a-a382-422f-a7f1-c6cece49ab25" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_CollaborativeArrangementThresholdForDevelopmentCostsPayments_67c22348-0c00-40e8-8be0-9a749966d59d" xlink:href="supn-20200331.xsd#supn_CollaborativeArrangementThresholdForDevelopmentCostsPayments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_88b48998-4d79-47c8-babf-d0ba7c70f547" xlink:to="loc_supn_CollaborativeArrangementThresholdForDevelopmentCostsPayments_67c22348-0c00-40e8-8be0-9a749966d59d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_c49ed3d8-2899-497b-9ce4-687e2aa65345" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_88b48998-4d79-47c8-babf-d0ba7c70f547" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_c49ed3d8-2899-497b-9ce4-687e2aa65345" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_4a7effef-6365-44f3-86fe-dd0a7477fd07" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_88b48998-4d79-47c8-babf-d0ba7c70f547" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_4a7effef-6365-44f3-86fe-dd0a7477fd07" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_b8d5b65c-ea12-4305-91af-a9f5c9b297d2" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_88b48998-4d79-47c8-babf-d0ba7c70f547" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsRangeOfOutcomesValueHigh_b8d5b65c-ea12-4305-91af-a9f5c9b297d2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_NumberOfEstablishedMarketedProducts_f70536f1-4257-49ad-8f37-4b9d6ee1d602" xlink:href="supn-20200331.xsd#supn_NumberOfEstablishedMarketedProducts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_88b48998-4d79-47c8-babf-d0ba7c70f547" xlink:to="loc_supn_NumberOfEstablishedMarketedProducts_f70536f1-4257-49ad-8f37-4b9d6ee1d602" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_NumberOfProductCandidates_b6438836-0888-4890-9f4f-c40e081b10db" xlink:href="supn-20200331.xsd#supn_NumberOfProductCandidates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_88b48998-4d79-47c8-babf-d0ba7c70f547" xlink:to="loc_supn_NumberOfProductCandidates_b6438836-0888-4890-9f4f-c40e081b10db" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_908baa72-7a76-472b-89d6-2d8d426c8009" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_88b48998-4d79-47c8-babf-d0ba7c70f547" xlink:to="loc_us-gaap_SubsequentEventTable_908baa72-7a76-472b-89d6-2d8d426c8009" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_9067dbf1-91ff-47d2-b474-6e92dc9dbe7e" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_908baa72-7a76-472b-89d6-2d8d426c8009" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_9067dbf1-91ff-47d2-b474-6e92dc9dbe7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_9067dbf1-91ff-47d2-b474-6e92dc9dbe7e_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_9067dbf1-91ff-47d2-b474-6e92dc9dbe7e" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_9067dbf1-91ff-47d2-b474-6e92dc9dbe7e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_66cf5708-e975-43bc-9e36-503c895bf26c" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_9067dbf1-91ff-47d2-b474-6e92dc9dbe7e" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_66cf5708-e975-43bc-9e36-503c895bf26c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_cd5a4df3-95bc-4173-95f3-043de139ae37" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_66cf5708-e975-43bc-9e36-503c895bf26c" xlink:to="loc_us-gaap_SubsequentEventMember_cd5a4df3-95bc-4173-95f3-043de139ae37" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_ccd23b6c-6c3d-418a-9743-d044cd038bed" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_908baa72-7a76-472b-89d6-2d8d426c8009" xlink:to="loc_srt_OwnershipAxis_ccd23b6c-6c3d-418a-9743-d044cd038bed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_ccd23b6c-6c3d-418a-9743-d044cd038bed_default" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_ccd23b6c-6c3d-418a-9743-d044cd038bed" xlink:to="loc_srt_OwnershipDomain_ccd23b6c-6c3d-418a-9743-d044cd038bed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_48c1feaa-f919-4d58-81fa-028ca7921c78" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_ccd23b6c-6c3d-418a-9743-d044cd038bed" xlink:to="loc_srt_OwnershipDomain_48c1feaa-f919-4d58-81fa-028ca7921c78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_NavitorPharmaceuticalsIncMember_3de1ddd0-6ab2-4a02-9152-f3b58ea4e13d" xlink:href="supn-20200331.xsd#supn_NavitorPharmaceuticalsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_48c1feaa-f919-4d58-81fa-028ca7921c78" xlink:to="loc_supn_NavitorPharmaceuticalsIncMember_3de1ddd0-6ab2-4a02-9152-f3b58ea4e13d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_2cb7a786-7784-4ad3-b480-87f04666f860" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_908baa72-7a76-472b-89d6-2d8d426c8009" xlink:to="loc_srt_CounterpartyNameAxis_2cb7a786-7784-4ad3-b480-87f04666f860" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_2cb7a786-7784-4ad3-b480-87f04666f860_default" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_2cb7a786-7784-4ad3-b480-87f04666f860" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_2cb7a786-7784-4ad3-b480-87f04666f860_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_2a5a9ef9-3b43-4b75-8ed6-54bb8698cc31" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_2cb7a786-7784-4ad3-b480-87f04666f860" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_2a5a9ef9-3b43-4b75-8ed6-54bb8698cc31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_NavitorPharmaceuticalsIncMember_8f3c21e5-f691-4cd3-9fdd-bf7064b476ff" xlink:href="supn-20200331.xsd#supn_NavitorPharmaceuticalsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_2a5a9ef9-3b43-4b75-8ed6-54bb8698cc31" xlink:to="loc_supn_NavitorPharmaceuticalsIncMember_8f3c21e5-f691-4cd3-9fdd-bf7064b476ff" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_ed3997fe-9738-4df4-be08-63cd714cc76b" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_908baa72-7a76-472b-89d6-2d8d426c8009" xlink:to="loc_us-gaap_TypeOfArrangementAxis_ed3997fe-9738-4df4-be08-63cd714cc76b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ed3997fe-9738-4df4-be08-63cd714cc76b_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_ed3997fe-9738-4df4-be08-63cd714cc76b" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_ed3997fe-9738-4df4-be08-63cd714cc76b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_225100d1-c43d-4bec-aefd-b0d55837fa49" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_ed3997fe-9738-4df4-be08-63cd714cc76b" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_225100d1-c43d-4bec-aefd-b0d55837fa49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CollaborativeArrangementTransactionWithPartyToCollaborativeArrangementMember_f8f080b5-947e-46d3-80f7-1e9e457a6b88" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_CollaborativeArrangementTransactionWithPartyToCollaborativeArrangementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_225100d1-c43d-4bec-aefd-b0d55837fa49" xlink:to="loc_us-gaap_CollaborativeArrangementTransactionWithPartyToCollaborativeArrangementMember_f8f080b5-947e-46d3-80f7-1e9e457a6b88" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_977968bc-1b24-4767-a002-e35c4f97ba0d" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_908baa72-7a76-472b-89d6-2d8d426c8009" xlink:to="loc_srt_RangeAxis_977968bc-1b24-4767-a002-e35c4f97ba0d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_977968bc-1b24-4767-a002-e35c4f97ba0d_default" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_977968bc-1b24-4767-a002-e35c4f97ba0d" xlink:to="loc_srt_RangeMember_977968bc-1b24-4767-a002-e35c4f97ba0d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_9bb9b065-148e-4b37-80fe-61b27a2c77ef" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_977968bc-1b24-4767-a002-e35c4f97ba0d" xlink:to="loc_srt_RangeMember_9bb9b065-148e-4b37-80fe-61b27a2c77ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_80489dd3-403d-4478-af34-acf3761ef887" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_9bb9b065-148e-4b37-80fe-61b27a2c77ef" xlink:to="loc_srt_MinimumMember_80489dd3-403d-4478-af34-acf3761ef887" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_3bd35861-a95d-4988-bd34-315d6cb45f8b" xlink:href="http://xbrl.fasb.org/srt/2019/elts/srt-2019-01-31.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_9bb9b065-148e-4b37-80fe-61b27a2c77ef" xlink:to="loc_srt_MaximumMember_3bd35861-a95d-4988-bd34-315d6cb45f8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_926ad1c6-dbe0-4360-8da2-845af36704b1" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_908baa72-7a76-472b-89d6-2d8d426c8009" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_926ad1c6-dbe0-4360-8da2-845af36704b1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_926ad1c6-dbe0-4360-8da2-845af36704b1_default" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_926ad1c6-dbe0-4360-8da2-845af36704b1" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_926ad1c6-dbe0-4360-8da2-845af36704b1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_774cf954-ec30-40c3-9825-e989b57f60a8" xlink:href="http://xbrl.fasb.org/us-gaap/2019/elts/us-gaap-2019-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_926ad1c6-dbe0-4360-8da2-845af36704b1" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_774cf954-ec30-40c3-9825-e989b57f60a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_supn_USWMEnterprisesLLCMember_fd60d7a4-ba85-4837-a923-69734092bba0" xlink:href="supn-20200331.xsd#supn_USWMEnterprisesLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_774cf954-ec30-40c3-9825-e989b57f60a8" xlink:to="loc_supn_USWMEnterprisesLLCMember_fd60d7a4-ba85-4837-a923-69734092bba0" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
