6-K

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549

Form 6-K

REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TO RULE 13a-16 OR 15d-16 UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of April 2026

Commission File Number: 001-39179

Addex Therapeutics Ltd (Translation of registrant's name into English)

Chemin des Mines 9, CH-1202 Geneva, Switzerland (Address of principal executive office)

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 [ X ]      Form 40-F [   ]

On April 23, 2026, the Registrant issued a press release, a copy of which is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

(c) Exhibit 99.1. Press release dated April 23, 2026

INCORPORATION BY REFERENCE

Exhibit 99.1 to this Report on Form 6-K shall be deemed to be incorporated by reference into the registration statement on Form F-3 (Registration No. 333-291644) of Addex Therapeutics Ltd and the registration statement on Form S-8 (Registration No. 333-255124 and No. 333-272515) of Addex Therapeutics Ltd (including any prospectuses forming a part of such registration statements) and to be a part thereof from the date on which this report is filed, to the extent not superseded by documents or reports subsequently filed or furnished.

RISK FACTORS

Our business faces significant risks. You should carefully consider all of the information set forth in this Report on Form 6-K and in our other filings with the United States Securities and Exchange Commission, or the SEC, including the risk factors related to our business set forth in our Annual Report on Form 20-F for the year ended December 31, 2024 filed with the Securities and Exchange Commission on May 15, 2025. Our business, financial condition, results of operations and growth prospects could be materially adversely affected by any of these risks. This report also contains forward-looking statements that involve risks and uncertainties. Our results could materially differ from those anticipated in these forward-looking statements, as a result of certain factors including the risks described in our Annual Report and our other SEC filings.

SIGNATURE

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.

EXHIBIT INDEX

EdgarFiling

EXHIBIT 99.1

Addex Spin-Out Company Neurosterix on Track to Complete Phase 1 Clinical Study of NTX-253 for Schizophrenia in Q2 2026

Ad Hoc Announcement Pursuant to Art. 53 LR

Geneva, Switzerland, April 23, 2026 - Addex Therapeutics (SIX: ADXN and Nasdaq: ADXN), a clinical-stage biopharmaceutical company focused on developing a portfolio of novel small molecule allosteric modulators for neurological disorders, today announced that its spin-out company, Neurosterix, is on track to complete its Phase 1 clinical study evaluating NTX-253 in Q2 2026. NTX-253 is an investigational potent, selective, orally available positive allosteric modulator (PAM) of the muscarinic M4 receptor being developed for the treatment of schizophrenia. The study is designed to generate a robust early-stage clinical data package assessing safety, tolerability, and pharmacokinetics (PK) across both healthy adult participants and those with stable schizophrenia.

The clinical study includes a multi-part, ascending-dose design intended to efficiently characterize NTX-253’s clinical profile and support subsequent patient-focused development. The study includes both single ascending dose (SAD) and multiple ascending dose (MAD) components, incorporating key translational elements such as food-effect and cerebrospinal fluid (CSF) assessments.

“This thoughtfully constructed Phase 1 clinical study has been designed to deliver a comprehensive understanding of NTX-253’s safety and pharmacokinetic profile, while incorporating early patient data and CNS exposure metrics,” said Tim Dyer, CEO of Addex. “We believe the study’s integrated, comprehensive design will help to de-risk subsequent clinical studies and could accelerate development timelines as it combines healthy volunteer and patient data within a single Phase 1 program.

Comprehensive Phase 1 Study Design Part 1: Single Ascending Dose (SAD) Healthy adult participants will receive a single oral dose of NTX-253 or placebo across sequentially escalating dose cohorts. This phase includes a dedicated food-effect cohort to assess the impact of food on NTX-253 pharmacokinetics. A separate SAD cohort in healthy volunteers will evaluate NTX-253 concentrations in cerebrospinal fluid, providing early insight into central nervous system exposure and brain penetration.

Part 2: Multiple Ascending Dose (MAD) In the MAD phase, participants will receive once-daily oral dosing of NTX-253 or placebo for 10 consecutive days, with sequential dose escalation. This phase is designed to evaluate safety, tolerability, and steady-state pharmacokinetics following repeated dosing.

Importantly, the MAD phase includes two dedicated cohorts of adults with stable schizophrenia, representing early clinical evaluation in the target patient population. Participants in these cohorts will have their antipsychotic medications withdrawn for up to eight days prior to dosing with NTX-253, enabling assessment of safety and PK in patients while maintaining clinical stability.

Neurosterix was spun-out of Addex in April 2024, raising $65 million in a Series A financing led by funds affiliated with Perceptive Advisors. Addex retains a 20% equity interest in Neurosterix.

About NTX-253 and M4 PAMs

The M4 muscarinic receptor is a validated target for treating schizophrenia and related disorders through indirect modulation of dopamine signaling. NTX-253 is a potent, selective, orally available PAM of M4 that fine-tunes muscarinic signaling with the potential to reduce psychosis symptoms while avoiding the movement disorders and metabolic complications associated with traditional dopamine antagonists. Preclinical studies demonstrate robust antipsychotic-like activity and a favorable safety profile, supporting progression into first-in-human clinical studies. Currently available antipsychotics typically target dopamine receptors, providing some success in ameliorating the positive symptoms of the disorder. However, targeting dopamine also can induce metabolic, cognitive, and motor side effects, limiting their therapeutic utility. Research suggest that M4 PAMs could indirectly modulate dopamine levels and induce antipsychotic activity without peripheral muscarinic side-effects seen with direct agonists. Highly selective M4 PAMs have been found to have robust antipsychotic-like effects in multiple rodent models and reverse multiple in vivo effects of psychomotor stimulants that induce increases in extracellular dopamine.

About Addex Therapeutics

Addex Therapeutics is a clinical-stage biopharmaceutical company focused on developing a portfolio of novel small molecule allosteric modulators for neurological disorders. Addex’s lead drug candidate, dipraglurant (mGlu5 negative allosteric modulator or NAM), is under evaluation for future development in brain injury recovery, including post-stroke and traumatic brain injury recovery. Addex’s partner, Indivior, has selected a GABAB PAM drug candidate for development in substance use disorders and has successfully completed IND enabling studies. Addex is advancing an independent GABAB PAM program for chronic cough. Addex holds a 20% equity interest in a private spin out company, Neurosterix LLC, which is advancing a portfolio of allosteric modulator programs, including M4 PAM for schizophrenia, psychosis and mood-related disorders and mGlu7 NAM for mood disorders. In addition, Addex has invested in Stalicla, a private Swiss company pioneering a precision medicine approach for neurodevelopmental and neuropsychiatric disorders.

Addex shares are listed on the SIX Swiss Exchange and American Depositary Shares representing its shares are listed on the NASDAQ Capital Market, and trade under the ticker symbol “ADXN” on each exchange. For more information, visit www.addextherapeutics.com.

Contacts:

Addex Forward Looking Statements:

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, as amended, including statements about the intended use of proceeds of the offering. The words “may,” “will,” “could,” “would,” “should,” “expect,” “plan,” “anticipate,” “intend,” “believe,” “estimate,” “predict,” “project,” “potential,” “continue,” “target” and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. Any forward-looking statements in this press release, are based on management's current expectations and beliefs and are subject to a number of risks, uncertainties and important factors that may cause actual events or results to differ materially from those expressed or implied by any forward-looking statements contained in this press release, including, without limitation, uncertainties related to market conditions. These and other risks and uncertainties are described in greater detail in the section entitled “Risk Factors” in Addex Therapeutics’ Annual Report on Form 20-F, prospectus and other filings that Addex Therapeutics may make with the SEC in the future. Any forward-looking statements contained in this press release represent Addex Therapeutics’ views only as of the date hereof and should not be relied upon as representing its views as of any subsequent date. Addex Therapeutics explicitly disclaims any obligation to update any forward-looking statements.