Company: SUPN
Filing Date: 2025-06-16
Form Type: SC TO-C
Source: 0001104659-25-059761
Chunk: 0

Company: SUPERNUS PHARMACEUTICALS, INC.
Filing Date: 2025-06-16
Form: SC TO-C
Chunk 0
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<div align='center'>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 13, 2025

Supernus Pharmaceuticals, Inc.

(Exact name of registrant
as specified in its charter)</div>

| Delaware                        | 001-35518   | 20-2590184                  |
| (State or other jurisdiction of 
 incorporation or organization)  | -Commission 
 File Number | -I.R.S.                     
 Employer Identification No. |

| 9715                            
 Key West Ave                    | Rockville | MD | 20850 |
| (Address                        
 of Principal Executive Offices) |           |    |  -Zip 
  Code |

<div align='center'>Registrant’s telephone
number, including area code: ( 301) 838-2500

Not Applicable

(Former name or former address,
if changed since last report.)</div>

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

| Title of                          
 each class                        | Trading Symbol | Name of each                 
 exchange on which registered |
| Common                            
 Stock, $0.001 par value per share | SUPN           | The Nasdaq                   
 Stock Market LLC             |

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)

x 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