Quantum Biopharma adds April release to registration

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 6-K/A REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TO RULE 13a-16 OR 15d-16 OF THE SECURITIES EXCHANGE ACT OF 1934 For the month of September 2026 Commission File Number: 001-39152 QUANTUM BIOPHARMA LTD. (Registrant) 1 Adelaide Street East, Suite 801 Toronto, Ontario M5C 2V9 (Address of Principal Executive Offices) Indicate by check mark whether the Registrant files or will file annual reports under cover of Form 20-F or Form 40-F. Form 20-F ☒ Form 40-F ☐ EXPLANATORY NOTE This Amendment No. 1 (this 'Amendment No. 1') to the report on Form 6-K originally furnished with the U.S. Securities and Exchange Commission on April 1, 2026, Accession Number 0001171843-26-002144 (the 'Initial Report'), is being furnished solely to incorporate Exhibit 99.1 filed as part of the Initial Report into the Registrant's Registration Statement on Form F-3 (File No. 333-276264). Except as set forth herein, there are no other changes to the Initial Report. 1 DOCUMENTS INCORPORATED BY REFERENCE Exhibit 99.1 included with this Amendment No. 1 is hereby incorporated by reference into the Registrant's Registration Statement on Form F-3 (File No. 333-276264) and shall be deemed to be a part thereof from the date on which the Initial Report was furnished, to the extent not superseded by documents or reports subsequently filed or furnished. 2 SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has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, thereunto duly authorized. QUANTUM BIOPHARMA LTD. (Registrant) Date: September 8, 2026 By /s/ Donal Carroll Donal Carroll Chief Financial Officer 3 EXHIBIT INDEX Exhibit Description of Exhibit 99.1 Press Release dated April 1, 2026 (incorporated by reference to Exhibit 99.1 to the Form 6-K furnished on April 1, 2026, Accession No. 0001171843-26-002144) 4