PepGen stock falls 41.13% after-hours after weak trial data and FDA clinical hold raise regulatory and efficacy concerns.

PepGen Inc. (NASDAQ: PEPG) plummeted 41.13% in after-hours trading following the release of underwhelming mid-stage trial data for its lead therapy, PGN-EDODM1, in myotonic dystrophy type 1. The trial reported only a marginal 7.3% average splicing correction at the 5 mg/kg dose, nearly identical to the placebo group. Compounding concerns, the FDA imposed a partial clinical hold on the U.S. study, citing issues in preclinical pharmacology and toxicology. The data and regulatory setback triggered immediate investor skepticism, further exacerbated by a securities fraud investigation being launched into the company’s handling of the trial developments. The stock’s sharp decline reflects a reassessment of the drug’s clinical and commercial viability ahead of anticipated higher-dose data in late 2026.