Quantum BioPharma Ltd-B美股招股说明书(2025-12-22版)

QUANTUM BIOPHARMA LTD. UP TO US$17,243,174CLASS B SUBORDINATE VOTING SHARES We have entered into an At The Market Offering Agreement, or the Sales Agreement, dated as of December 22, 2025, with Rodman &Renshaw LLC, or Rodman or the Sales Agent, relating to the offering of our Class B Subordinate Voting Shares, or the Class B Shares,pursuant to this prospectus supplement and the accompanying base prospectus. In accordance with the terms of the Sales Agreement,we may offer and sell our Class B Shares having an aggregate offering price of up to US$17,243,174, from time to time through or tothe Sales Agent, acting as sales agent or principal. Our Class B Shares are listed for trading under the trading symbol “QNTM” on the Nasdaq Capital Market, or Nasdaq, in the UnitedStates, and listed and posted for trading in Canada on the Canadian Securities Exchange, or the CSE, under the trading symbol“QNTM”. Our Class B Shares are also listed and posted for trading in Germany on the Börse Frankfurt (or Frankfurt Stock Exchange),or the FSE, under the trading symbol “0K91”. On December 19, 2025, the closing price of our Class B Shares was US$8.89 per shareon Nasdaq, C$12.32 per share on the CSE, and €7.10 per share on the FSE. Upon our delivery of a sales notice and subject to the terms and conditions of the Sales Agreement, the Sales Agent may sell our ClassB Shares by methods deemed to be an “at the market offering” as defined in Rule 415(a)(4) promulgated under the U.S. Securities Actof 1933, as amended, or the Securities Act, including sales made directly on or through Nasdaq, the existing trading market for ourClass B Shares in the United States, sales made to or through a market maker other than on an exchange or otherwise, directly toRodman as principal, in negotiated transactions at market prices prevailing at the time of sale or at prices related to such prevailingmarket prices, and/or through any other method permitted by law. See “Plan of Distribution.” The Sales Agent is not required to sellany specific number or amount of Class B Shares, but will use its commercially reasonable efforts consistent with its normal tradingand sales practices and applicable state and federal laws, rules and regulations and the rules of Nasdaq. There is no arrangement forfunds to be received in any escrow, trust or similar arrangement. No sales of our Class B Shares under this prospectus supplement and the accompanying base prospectus will be made in Canada orover or through the facilities of the CSE or any other exchange or market in Canada. We will pay the Sales Agent a commission for its services in acting as agent in the sale of Class B shares of up to 3.0% of the grosssales price per share of all shares sold through the Sales Agent as agent under the Sales Agreement. See “Plan of Distribution” forinformation relating to certain expenses of the Sales Agent to be reimbursed by us. In connection with the sale of the Class B Shareson our behalf, the Sales Agent will be deemed to be an “underwriter” within the meaning of the Securities Act and the compensation tothe Sales Agent will be deemed to be underwriting commissions or discounts. We have also agreed to provide indemnification andcontribution to the Sales Agent with respect to certain liabilities, including liabilities under the Securities Act and the U.S. SecuritiesExchange Act of 1934, as amended, or the Exchange Act. This offering pursuant to this prospectus supplement and the accompanyingbase prospectus will terminate upon the earlier of (a) the sale of the Series B Shares pursuant to this prospectus supplement and theaccompanying base prospectus having an aggregate sales price of $17,243,174, or (b) the termination by us or the Sales Agent of theSales Agreement pursuant to its terms. As of the date of this prospectus supplement, the aggregate market value of our outstanding common equity held by non-affiliates, orour public float, was approximately US$51,729,523 based on a total of 42 Class A Multiple Voting Shares and 3,842,935 Class BShares outstanding, of which 3,582,377 Class B Shares were held by non-affiliates, at a price of US$14.44 per share, the closing salesprice of our Class B Shares on October 23, 2025, which is the highest closing price of our Class B Shares on Nasdaq within the prior60 days. Pursuant to General Instruction I.B.5. of FormF-3, in no event will we sell our securities in a public primary offering inreliance on General Instruction I.B.5. of FormF-3 with a value exceeding one-third of our public float in any 12-calendar-monthperiod so long as our public float remains below US$75.0 million. During the 12 calendar months prior to and including the date ofthis prospectus supplement, we have not offered or sold any securities pursuant to General Instruction I.B.5 of Form F-3.As a result,we may sell up to US$17,243,174 of our Class B Shares hereunder. We are an “emerging growth company” and a “foreign private issuer” as defined under U.S. fede