Biogen shares fell on Friday after the head of the Food and Drug Administration called for an investigation into the recent approval of the company’s Alzheimer’s drug, Aduhelm.

Acting FDA Commissioner Dr. Janet Woodcock asked the Office of the Inspector General to investigate interactions between the U.S. agency and Biogen representatives prior to the drug’s approval on June 7.

“I believe that it is critical that the events at issue be reviewed by an independent body such as the Office of the Inspector General in order to determine whether any interactions that occurred between Biogen and FDA review staff were inconsistent with FDA policies and procedures,” Woodcock wrote in a letter sent Friday.

Shares of Biogen fell by more than 3% after the announcement.

Biogen’s stock surged last month after the FDA approved the biotech company’s drug, the first medication cleared by U.S. regulators to slow cognitive decline in people living with Alzheimer’s and the first new medicine for the disease in nearly two decades.

That decision marked a departure from the advice of the agency’s independent panel of outside experts, who unexpectedly declined to endorse the drug last fall, citing unconvincing data. At least three members of the panel have resigned in protest following the agency’s approval.

Federal regulators faced intense pressure from friends and family members of Alzheimer’s patients asking to fast-track the drug, scientifically known as aducanumab. STAT News and other media outlets reported FDA officials used a regulatory shortcut to gain approval in order to get the drug on the market sooner.

Biogen’s drug targets a “sticky” compound in the brain known as beta-amyloid, which scientists expect plays a role in the devastating disease. 

It’s rare for an FDA chief to call for an investigation into the agency’s own decisions. It’s the latest setback for the company and the drug, which has been controversial since it showed promise in 2016.

In March 2019, Biogen pulled development of the drug after an analysis from an independent group revealed it was unlikely to work. The company then shocked investors several months later by announcing it would seek regulatory approval for the medication after all.

When Biogen sought approval for the drug in late 2019, its scientists said a new analysis of a larger dataset showed aducanumab “reduced clinical decline in patients with early Alzheimer’s disease.”

Alzheimer’s experts and Wall Street analysts were immediately skeptical, with some wondering whether the clinical trial data was enough to prove the drug works and whether approval could make it harder for other companies to enroll patients in their own drug trials.

Some doctors have said they won’t prescribe aducanumab because of the mixed data package supporting the company’s application.