Sanofi shares slide as FDA delays MS drug decision and late-stage trial disappoints

Shares of French pharmaceutical group Sanofi fell sharply on Monday after the company flagged another delay to a US regulatory decision for its experimental multiple sclerosis drug tolebrutinib and reported disappointing results from a late-stage clinical trial.

The stock dropped as much as 5% in early trading, making it the worst performer on Paris’s SBF 120 index, before trimming losses to trade about 4% lower.

The update marks a setback for one of Sanofi’s most closely watched pipeline assets as the company seeks to rebuild momentum following a string of trial disappointments.

FDA review pushed back again

Sanofi said discussions with the US Food and Drug Administration indicated that a regulatory review of tolebrutinib for non-relapsing secondary progressive multiple sclerosis would extend beyond a target action date of December 28.

The company now expects further guidance from the FDA by the end of the first quarter of 2026.

This represents the second delay to a decision initially expected in September, before being pushed to late December.

Sanofi had already disclosed in September that the FDA had extended its review by three months.

Tolebrutinib was granted breakthrough therapy designation by the FDA last December, a status intended to speed the development of drugs that address serious conditions with unmet medical needs.

The treatment is also under regulatory review in the European Union and received provisional approval in the United Arab Emirates in July.

Late-stage trial misses key target

Adding to investor concerns, Sanofi said tolebrutinib failed to meet its primary endpoint in a late-stage trial involving patients with primary progressive multiple sclerosis.

The study showed the drug did not significantly slow disability progression in this form of the disease, which accounts for roughly 10% of multiple sclerosis cases.

As a result, Sanofi said it would not pursue regulatory registration for tolebrutinib in primary progressive multiple sclerosis.

The company will also assess whether it needs to book an impairment charge on the asset’s value.

“We are disappointed by today’s results; however, we do believe that these results will improve our understanding of the underlying disease biology of multiple sclerosis,” said Houman Ashrafian, Sanofi’s head of research and development.

Focus shifts to remaining opportunity

Despite the trial failure, Sanofi stressed that it remains confident in the potential of tolebrutinib for non-relapsing secondary progressive multiple sclerosis, a condition in which patients no longer experience relapses but continue to accumulate disability.

Jefferies analysts described the trial outcome as a negative surprise but said the larger commercial opportunity still lay in this patient group.

Analysts had previously seen a path for the drug to generate more than €1 billion in annual sales by 2030, according to consensus estimates compiled by Visible Alpha.

Sanofi said its 2025 guidance remains unchanged and that any potential impairment test would not affect business net profit, which excludes one-off items.

Pipeline pressure and dealmaking

The latest developments underscore the pressure on Sanofi’s drug pipeline as it works to move past recent clinical setbacks.

The company has increasingly turned to dealmaking this year, using proceeds from the sale of a controlling stake in its consumer healthcare business to bolster its portfolio.

For now, the market reaction reflects uncertainty over whether tolebrutinib can still deliver on its promise, even as Sanofi argues that its remaining data support continued development in a narrower, but still significant, segment of multiple sclerosis patients.