Addex Therapeutics Files Prospectus To Offer And Sell Ads For Up To $3.3M From Time To Time

Up to $3,300,000American Depositary Shares Representing Ordinary Shares

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We have entered into an At The Market Offering Agreement, or the sales agreement, dated January 30, 2024, with H.C. Wainwright & Co., LLC, or H.C. Wainwright, relating to offer and sale of American Depositary Shares, or ADSs, each representing one hundred and twenty of our ordinary shares, no nominal value, from time to time through H.C. Wainwright acting as sales agent or principal. In accordance with the terms of the sales agreement, under this prospectus supplement and the accompanying prospectus, we may offer and sell ADSs having a maximum aggregate offering price of up to $3,300,000 from time to time through H.C. Wainwright in this offering, acting as our sales agent.

The ADSs are traded on the Nasdaq Capital Market, or Nasdaq, under the symbol "ADXN". Each ADS represents the right to receive one hundred and twenty ordinary shares of Addex Therapeutics Ltd. On December 9, 2025, the last reported sales price of our ADSs on Nasdaq was $7.35 per ADS. Our ordinary shares are listed on the SIX Swiss Exchange, or SIX, under the symbol "ADXN." On December 9, 2025, the last reported sales price of our ordinary shares on SIX was CHF 0.054 or $0.067 per share (based on the exchange rate between the Swiss franc and the U.S dollar reported on such date, which was $1.24 per CHF 1.0).

Sales of the ADSs representing our ordinary shares, if any, under this prospectus supplement and the accompanying prospectus will be made in sales deemed to be an "at the market offering" as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended, or the Securities Act, including sales made directly on or through Nasdaq or any other existing trading market in the United States for the ADSs, sales made to or through a market maker other than on an exchange or otherwise, directly to H.C. Wainwright as principal, in negotiated transactions at market prices prevailing at the time of sale or at prices related to such prevailing market prices and/or in any other method permitted by law. If we and H.C. Wainwright agree on a method of distribution other than sales of the ADSs on or through Nasdaq or another existing trading market in the United States at market prices, we will file a further prospectus supplement providing all information about such offering as required by Rule 424(b) under the Securities Act. H.C. Wainwright is not required to sell any specific number or dollar amount of ADSs, but will act as our sales agent using commercially reasonable efforts to sell on our behalf all of the ADSs requested to be sold by us, consistent with its normal trading and sales practices and applicable laws and regulations, subject to the terms and conditions of the sales agreement on mutually agreed terms. There is no arrangement for funds to be received in any escrow, trust or similar arrangement. This offering pursuant to this prospectus supplement and the accompanying prospectus will terminate upon the earlier of (1) the sale of ADSs pursuant to this prospectus supplement having an aggregate sales price of $3,300,000 and (2) the termination by us or H.C. Wainwright of the sales agreement pursuant to its terms. We provide more information about how the ADSs will be sold in the section entitled "Plan of Distribution."

H.C. Wainwright will be entitled to cash compensation at a fixed commission rate equal to 3.0% of the gross sales price of the ADSs sold through H.C. Wainwright under the sales agreement. In connection with the sales of ADSs on our behalf, H.C. Wainwright will be deemed to be an "underwriter" within the meaning of the Securities Act, and the compensation paid to H.C. Wainwright will be deemed to be underwriting commissions or discounts. We have agreed to provide indemnification and contribution to H.C. Wainwright against certain liabilities, including liabilities under the Securities Act. We have also agreed to reimburse certain of H.C. Wainwright's expenses in connection with the offering as further described in the "Plan of Distribution" section beginning on page S-30 of this prospectus supplement.

Under the registration statement to which this prospectus supplement forms a part, we may not sell our securities in a primary offering with a value exceeding one-third of our public float in any 12-calendar month period (unless our public float rises to $75.0 million or more). The aggregate market value of our outstanding voting and nonvoting common equity held by non-affiliates computed in accordance with General Instruction I.B.5 to Form F-3 is $9.95 million, based on 125,588,452 shares held by non-affiliates and a CHF 0.063 ($0.079) closing price of the shares on SIX on November 13, 2025. During the 12 full calendar months preceding and including the date of this prospectus supplement, we have not sold any securities under General Instructions I.B.5 to Form F-3.

The ADSs offered hereby comprise a portion of the $150.0 million aggregate value of securities registered for issuance on a primary basis on the registration statement of which this prospectus supplement and the accompanying prospectus form a part.

We are an "emerging growth company" as defined by the Jumpstart Our Business Startups Act of 2012 and, as such, we have elected to comply with certain reduced public company reporting requirements for this prospectus supplement and future filings. However, we have elected not to take advantage of the extended transition period allowed for emerging growth companies for complying with new or revised accounting guidance as allowed by Section 107 of the JOBS Act and Section 7(a)(2)(B) of the Securities Act. See the section entitled "Prospectus Supplement Summary — Implications of Being an Emerging Growth Company and a Foreign Private Issuer" for additional information.