Company: SUPN
Filing Date: 2025-10-16
Form Type: 8-K/A
Source: 0001356576-25-000062
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Company: SUPERNUS PHARMACEUTICALS, INC.
Filing Date: 2025-10-16
Form: 8-K/A
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### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION

#### Washington, D.C. 20549

#### FORM 8-K/A

### CURRENT REPORT
<div align='center'>Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): July 31, 2025</div>

#### Supernus Pharmaceuticals, Inc.
<div align='center'>(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</div>

#### Not Applicable
<div align='center'>(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)

☐ 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