Sanofi Stock Plummets as Multiple Sclerosis Drug growth Falters, Regulatory Delays Mount
Sanofi shares experienced a notable downturn this week following the company’s announcement that it is abandoning development of tolebrutinib for primary progressive multiple sclerosis (PPMS) and facing further delays in the regulatory review of the drug for a different form of the disease. The setbacks represent a fresh wave of disappointment for the French pharmaceutical giant, which has struggled with clinical trial results throughout 2025.
The company’s stock fell 3% in morning trading on the Paris Stock Exchange, marking the largest drop in the CAC 40 index, and at one point declining as much as 5.4%. This latest decline adds to a challenging year for Sanofi, with its stock down 13.6% making it one of the worst performers in the CAC 40.
The decision to halt development for PPMS comes after the “PERSEUS” trial evaluating tolebrutinib for PPMS – a rarer, more aggressive form of MS that lacks remission phases – failed to meet its primary endpoint. According to a company release,the “PERSEUS” trial demonstrated no significant delay in the progression of disability after six months of treatment compared to a placebo group. Consequently,Sanofi has decided not to pursue regulatory approval for tolebrutinib in PPMS.
“The failure of the PERSEUS study in primary progressive multiple sclerosis (PPMS) is a disappointment after the success of tolebrutinib in the HERCULES trial,” noted a report from UBS. The HERCULES trial, which evaluated tolebrutinib for nrMSP, had yielded positive results in September 2024.
Adding to the concerns, Sanofi also announced a delay in the review of tolebrutinib for nrMSP by the U.S.Food and Drug Administration (FDA). The FDA had already postponed a target review date from September 28 to December 28, 2025, citing the need for additional analyses. Now, the agency indicates the review will extend beyond that date, with further guidance expected by the end of the first quarter of 2026.
Analysts at Oddo BHF suggest the delay “may raise questions, especially in terms of product safety and thus the ultimately label of the medicine,” while also acknowledging that a recent government shutdown in the U.S. could have contributed to the slowdown.
The potential market for tolebrutinib had been estimated at €1.4 billion by analysts, with UBS projecting peak annual sales of $1 billion for both PPMS and nrMSP. Though, the recent setbacks have cast doubt on these projections.”The question now is whether the FDA will be satisfied with the effectiveness demonstrated in the case of nrMS and the safety data from all studies in multiple sclerosis, or if the inability to demonstrate a benefit in the case of PPMS reduces the chances of tolebrutinib to obtain authorization for the treatment of nrMS,” UBS analysts stated.
despite the challenges, Jefferies remains relatively optimistic, arguing that “the story is not over for nrMSP” due to the significant unmet medical need in this area.
This latest news follows a series of disappointing clinical trial results for Sanofi in 2025. In May, data from trials evaluating itepekimab for chronic obstructive pulmonary disease (COPD) were mixed, with one study showing positive results and the other failing to meet its criteria. Then, in September, results for amlitelimab, a potential treatment for atopic dermatitis, fell short of expectations.
“The market is saying that this is another failure for Sanofi,” one financial intermediary confirmed. “Given the group’s ‘track record’ in terms of clinical trials,we could not be as optimistic as for the other major laboratories.” Bank of America analysts echoed this sentiment, stating that the recent announcements “continue the disappointing data regarding the pipeline of Sanofi.”
The series of setbacks raises concerns about Sanofi’s research and development pipeline and its ability to deliver on future growth prospects. While the future of tolebrutinib remains uncertain, the company faces mounting pressure to revitalize its pipeline and restore investor confidence.
