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Amphastar Pharmaceuticals, Inc._February 26, 2026 0001297184false00012971842026-02-262026-02-26 ​ ​

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): February 26, 2026 ​ Amphastar Pharmaceuticals, Inc. (Exact Name of Registrant as Specified in Charter) ​ ​

​

​

Delaware 001-36509 33-0702205

(State or Other Jurisdiction of Incorporation) (Commission File Number) (I.R.S. Employer Identification Number)

​ ​ ​

​

11570 6th Street ​

Rancho Cucamonga, California 91730

(Address of Principal Executive Offices) (Zip Code)

​ Registrant's telephone number, including area code: (909) 980-9484 ​ ​ ​ 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: ​ ☐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)) ​ Securities registered pursuant to Section 12(b) of the Act:

​

​

​

​

​

​

​

​

​

​

​

​

Title of each class ​ Trading Symbol(s) ​ Name of each exchange on which registered

Common Stock, par value $0.0001 per share ​

AMPH

​ The NASDAQ Stock Market LLC

​ 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). ​ Emerging growth company ☐ ​ 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. ☐ ​ ​ ​ ​

Item 2.02. Results of Operations and Financial Condition. ​ On February 26, 2026, Amphastar Pharmaceuticals, Inc. issued a press release announcing its financial results for the three months and fiscal year ended December 31, 2025. A copy of the press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K. ​ The information in this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing. ​ Item 9.01. Financial Statements and Exhibits. ​ (d) Exhibits: ​ ​

​

​

Exhibit No. ​ ​ ​ Description

99.1 ​ Press release, dated February 26, 2026, issued by Amphastar Pharmaceuticals, Inc.

104 ​ Cover Page Interactive Data File (embedded within the Inline XBRL document)

​ ​ ​

SIGNATURE

​ 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. ​ ​

​

​

​

Date: February 26, 2026 Amphastar Pharmaceuticals, Inc.

​ ​

​ By: /s/ WILLIAM J. PETERS

​ ​ William J. Peters

​ ​ Chief Financial Officer, Executive Vice President and Treasurer

​ ​ ​

Amphastar Pharmaceuticals, Inc._November 6, 2025 0001297184falseDE00012971842025-11-062025-11-06 ​ ​

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): November 6, 2025 ​ Amphastar Pharmaceuticals, Inc. (Exact Name of Registrant as Specified in Charter) ​ ​

​

​

Delaware 001-36509 33-0702205

(State or Other Jurisdiction of Incorporation) (Commission File Number) (I.R.S. Employer Identification Number)

​ ​ ​

​

11570 6th Street ​

Rancho Cucamonga, California 91730

(Address of Principal Executive Offices) (Zip Code)

​ Registrant's telephone number, including area code: (909) 980-9484 ​ ​ ​ 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: ​ ☐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)) ​ Securities registered pursuant to Section 12(b) of the Act:

​

​

​

​

​

​

​

​

​

​

​

​

Title of each class ​ Trading Symbol(s) ​ Name of each exchange on which registered

Common Stock, par value $0.0001 per share ​

AMPH

​ The NASDAQ Stock Market LLC

​ 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). ​ Emerging growth company ☐ ​ 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. ☐ ​ ​ ​ ​

Item 2.02. Results of Operations and Financial Condition. ​ On November 6, 2025, Amphastar Pharmaceuticals, Inc. issued a press release announcing its financial results for the three months ended September 30, 2025. A copy of the press release is furnished as Exhibit 99.1 to this Current Report on Form 8-K. ​ The information in this Current Report on Form 8-K, including Exhibit 99.1, shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such a filing. ​ Item 9.01. Financial Statements and Exhibits. ​ (d) Exhibits: ​ ​

​

​

Exhibit No.

Description

99.1 ​ Press release, dated November 6, 2025, issued by Amphastar Pharmaceuticals, Inc.

104 ​ Cover Page Interactive Data File (embedded within the Inline XBRL document)

​ ​ ​

SIGNATURE

​ 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. ​ ​

​

​

​

Date: November 6, 2025 Amphastar Pharmaceuticals, Inc.

​ ​

​ By: /s/ WILLIAM J. PETERS

​ ​ William J. Peters

​ ​ Chief Financial Officer, Executive Vice President and Treasurer

​ ​ ​