UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): June 17, 2022

Supernus Pharmaceuticals, Inc.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (301) 838-2500

Not Applicable

(Former name or former address, if changed since last report.)

Securities registered pursuant to Section 12(b) of the Exchange Act

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter). ¨

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ¨

On June 17, 2022, Supernus Pharmaceuticals, Inc. (the “Company”) held its annual meeting of stockholders (the “Annual Meeting”). The definitive proxy statement pertaining to the Annual Meeting was previously filed by the Company with the Securities and Exchange Commission on May 2, 2022. As of the close of business on April 18, 2022, there were 53,407,811 shares of common stock outstanding and entitled to vote. The tabulation of votes for each proposal voted on by the stockholders was as follows:

Proposal 1: Election of Class I Directors, each to serve until the Annual Meeting of the Company in 2025.

Proposal 2: Ratification of the appointment of KPMG LLP as the Company’s independent public accounting firm for the fiscal year ending December 31, 2022.

Proposal 3: To approve, on a non-binding basis, the compensation paid to our named executive officers.

Exhibit 104 — The cover page from this Current Report on Form 8-K, formatted in Inline XBRL.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.