Company: GANX
Filing Date: 2025-11-28
Form Type: 424B5
Source: 0001104659-25-116944
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Company: Gain Therapeutics, Inc.
Filing Date: 2025-11-28
Form: 424B5
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TABLE OF CONTENTS

#### Filed Pursuant to Rule 424(b)(5)

#### Registration No. 333-287622

### PROSPECTUS SUPPLEMENT
**(To Prospectus Dated November 26, 2025)**

<div align='center'>**$35,530,980.56**</div>

#### Common Stock
On September 6, 2024, we entered into an Equity Distribution Agreement, or the Distribution Agreement, with Oppenheimer & Co. Inc., or Oppenheimer, relating to our common stock having an aggregate offering price of up to $50 million. On September 6, 2024, pursuant to the Distribution Agreement, we filed a prospectus supplement pursuant to which we could offer and sell from time to time shares of our common stock having an aggregate offering price of up to $50 million through Oppenheimer. As of November 28, 2025, of the $50 million of our common stock covered by the Distribution Agreement and the related prospectus supplement, dated September 6, 2024 to the Company’s Registration Statement on Form S-3 (333-265061), we have issued and sold an aggregate of 6,393,341 shares of our common stock for gross proceeds of $14,469,019.44.

With the filing of this prospectus supplement, we are replacing and superseding the prior prospectus supplement, and all sales of our common stock pursuant to the Distribution Agreement shall be pursuant to this prospectus supplement and the accompanying base prospectus. This prospectus supplement and the accompanying base prospectus, which together we sometimes refer to as the prospectus, relates to the offer and sale, from time to time, of shares of our common stock having an aggregate gross sales price of up to $35,530,980.56 through Oppenheimer in accordance with the terms of the Distribution Agreement.

Our common stock is listed on The Nasdaq Global Market, or Nasdaq, under the symbol “GANX.” On November 26, 2025, the closing sale price of our common stock on Nasdaq was $3.14 per share.

Sales of our common stock, if any, under this prospectus supplement may be made by any method 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. Oppenheimer is not required to sell any specific number or dollar amount of