Company: SUPN
Filing Date: 2025-04-30
Form Type: DEFA14A
Source: 0001104659-25-042541
Chunk: 0

Company: SUPERNUS PHARMACEUTICALS, INC.
Filing Date: 2025-04-30
Form: DEFA14A
Chunk 0
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<div align='center'>UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

PROXY STATEMENT PURSUANT TO SECTION 14(a) OF
THE

SECURITIES EXCHANGE ACT OF 1934</div>

FILED BY THE REGISTRANT x

FILED BY A PARTY OTHER THAN THE REGISTRANT ¨

Check the appropriate box:

| ¨ | Preliminary Proxy Statement |

| ¨ | Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) |

| ¨ | Definitive Proxy Statement |

| x | Definitive Additional Materials |

| ¨ | Soliciting Material under §240.14a-12 |

<div align='center'>SUPERNUS PHARMACEUTICALS, INC.

(Name of the Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement,
if other than the Registrant)</div>

Payment of Filing Fee (Check the appropriate box):

| x | No fee required. |

| ¨ | Fee paid previously with preliminary materials. |

| ¨ | Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a6(i)(1) and 
 0-11.                                                                                         |

| Here’s how to order a copy of the proxy materials and select delivery preferences:                                                          
 Current and future delivery requests can be submitted using the options below.                                                              
 If you request an email copy, you will receive an email with a link to the current meeting materials.                                       
 PLEASE NOTE: You must use the number in the shaded bar on the reverse side when requesting a copy of the proxy materials.                   
 — Internet – Go to www.investorvote.com/SUPN.                                                                                               
 — Phone – Call us free of charge at 1-866-641-4276.                                                                                         
 — Email – Send an email to investorvote@computershare.com with “Proxy Materials Supernus Pharmaceuticals, Inc.” in the subject line.        
 Include your full name and address, plus the number located in the shaded bar on the reverse side, and state that you want a paper          
 copy of the meeting materials.                                                                                                              
 To facilitate timely delivery, requests for a paper copy of proxy materials must be received by June 6, 2025.                               
 The 2025 Annual Meeting of Stockholders of Supernus Pharmaceuticals, Inc. will be