MoonLake Immunotherapeutics (MLTX) saw its stock price plummet by 5.10% in Thursday's intraday trading, as investors reacted to news of a class action lawsuit filed against the company. The lawsuit alleges that MoonLake engaged in securities fraud, potentially shaking investor confidence in the biopharmaceutical firm.

The class action, filed on behalf of investors who purchased MoonLake securities between March 10, 2024, and September 29, 2025, centers around alleged false statements and concealed information regarding the company's sole drug candidate, SLK. The lawsuit claims that MoonLake failed to disclose critical information about SLK's similarities to an existing drug, BIMZELX, and overstated the potential benefits of SLK's Nanobody structure.

Specifically, the complaint alleges that MoonLake did not reveal that SLK and BIMZELX share the same molecular targets, and that SLK's purported unique structure would not provide superior clinical benefits over BIMZELX. Furthermore, the lawsuit contends that the company's claims about SLK's increased tissue penetration leading to improved clinical efficacy were unfounded. These allegations suggest that MoonLake may have lacked a reasonable basis for its positive statements about SLK's advantages over monoclonal antibodies, potentially misleading investors about the drug's prospects.