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rytm-202602260001649904false00016499042026-02-262026-02-26

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

RHYTHM PHARMACEUTICALS, INC.

(Exact name of registrant as specified in its charter)

Delaware001-3822346-2159271 (State or other jurisdiction of incorporation)(Commission File Number)(IRS Employer Identification Number)

222 Berkeley Street 12th Floor Boston, MA 02116 (Address of principal executive offices) (Zip Code) Registrant’s telephone number, including area code: (857) 264-4280 N/A (Former name or former address, if changed since last report) 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 classTrading Symbol(s)Name of each exchange on which registered Common Stock, $0.001 par value per shareRYTMThe Nasdaq Stock Market LLC (Nasdaq Global Market)

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, Rhythm Pharmaceuticals, Inc. (the “Company”) announced its financial results for the fourth quarter and full year ended December 31, 2025. The full text of the press release issued by the Company in connection with the announcement is furnished as Exhibit 99.1 to this Current Report on Form 8-K (the “Current Report”). The information contained in Item 2.02 of this Current Report (including Exhibit 99.1 attached hereto) 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 (the “Securities Act”), or the Exchange Act, except as expressly provided by specific reference in such a filing.

Item 9.01. Financial Statements and Exhibits. (d) Exhibits The following Exhibit 99.1 relates to Item 2.02 and shall be deemed to be furnished, and not filed:

Exhibit No.Description 99.1Press release dated February 26, 2026

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

SIGNATURES

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

RHYTHM PHARMACEUTICALS, INC.

Date: February 26, 2026By:/s/ Hunter C. Smith Hunter C. Smith Chief Financial Officer

rytm-202601090001649904false00016499042026-01-092026-01-09

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): January 9, 2026

RHYTHM PHARMACEUTICALS, INC.

(Exact name of registrant as specified in its charter)

Delaware

001-38223

46-2159271

(State or other jurisdiction of incorporation)

(Commission File Number)

(IRS Employer Identification Number)

222 Berkeley Street 12th Floor Boston, MA 02116 (Address of principal executive offices) (Zip Code) Registrant’s telephone number, including area code: (857) 264-4280 N/A (Former name or former address, if changed since last report) 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, $0.001 par value per share

RYTM

The Nasdaq Stock Market LLC (Nasdaq Global Market)

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 January 9, 2026, Rhythm Pharmaceuticals, Inc. (the “Company”) issued a press release announcing, among other things, the Company’s preliminary unaudited net product revenues for the fourth quarter of 2025 and the fiscal year ended December 31, 2025. The full text of the press release issued by the Company is furnished as Exhibit 99.1 to this Current Report on Form 8-K. The information contained in Item 2.02 of 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 (the “Securities Act”), or the Exchange Act, except as expressly provided by specific reference in such a filing.

Item 7.01. Regulation FD Disclosure. On January 9, 2026, in connection with its participation in the J.P. Morgan Healthcare Conference, the Company posted a corporate slide presentation in the “Investors” portion of its website at www.rhythmtx.com. A copy of the presentation is furnished as Exhibit 99.2 to this Current Report on Form 8-K. The Company undertakes no obligation to update, supplement or amend the materials attached hereto as Exhibit 99.2. The information contained in Item 7.01 of this Current Report on Form 8-K (including Exhibit 99.2) shall not be deemed “filed” for purposes of Section 18 of 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, or the Exchange Act, except as expressly provided by specific reference in such a filing.

Item 8.01. Other Events On January 9, 2026, the Company announced preliminary unaudited net revenues from global sales of IMCIVREE® (setmelanotide) of approximately $57 million for the fourth quarter of 2025, an increase of 11% percent on a sequential basis from the third quarter of 2025.  Net product revenues for the full year of 2025 are expected to be approximately $194 million, compared to $130 million for the full year of 2024, an increase of approximately 50% year over year. U.S. sales of IMCIVREE contributed approximately 68% of fourth quarter preliminary unaudited net product revenues and approximately 69% of full-year 2025 preliminary unaudited net product revenues. The Company also provided an update on anticipated upcoming milestones: Setmelanotide Acquired Hypothalamic Obesity (HO) •Launch IMCIVREE in the United States for the treatment of acquired hypothalamic obesity pending FDA approval; the FDA’s assigned PDUFA goal date is March 20, 2026; •Announce topline data in the 12-patient Japanese cohort of the setmelanotide Phase 3 trial in acquired HO in the first quarter of 2026. Congen