WASHINGTON (AP) — A much-debated drug for Lou Gehrig’s disease won U.S. approval Thursday, a long-sought victory for patients that is likely to renew questions about the scientific rigor behind government reviews of experimental medicines.

Amylyx Pharmaceuticals said the Food and Drug Administration approved the drug for adults with amyotrophic lateral sclerosis, or ALS, which destroys nerve cells needed for basic functions like walking, talking and swallowing. It is only the third U.S.-approved medicine for ALS.

The FDA based the approval on one small, mid-stage study in which patients appeared to progress more slowly against the debilitating disease. Typically, the FDA requires two large studies or one study with “very persuasive” results for approval.

The FDA’s review has become a flashpoint in broader debates about the regulatory agency, including how flexible it should be when reviewing drugs for deadly diseases and how much weight it should give to appeals from patients and other outside voices.

“I think it demonstrates the FDA’s ability to be facile and I think it demonstrates a lot of tenacity on the part of ALS patients and advocates,” said Dr. Catherine Lomen-Hoerth, an ALS specialist at the University of California San Francisco. “The company really tried to do everything possible to get this potentially promising drug out to patients.”

Amylyx’s drug is the latest in a string of neurological drugs that have won FDA approval despite questionable effectiveness data. The agency is still facing two government probes into its approval of the Alzheimer’s drug Aduhelm last year, which has not yet been shown to slow the disease.

The latest FDA drug approval followed a remarkably turbulent path to market, including two negative reviews by the FDA internal scientists, who called the company’s results “borderline” and “not persuasive.” A panel of outside advisers backed that negative opinion in March, narrowly voting against the drug.

But the FDA has faced intense pressure from ALS patients, advocates and members of Congress. In recent weeks the agency received more than 1,300 written comments from the ALS community supporting the treatment.

That outpouring helped sway the same expert panel when FDA reconvened them earlier month to revisit Amylyx’s drug. The second time around, they backed the drug, 7-2. The vote was not binding, but it seemed to open the door for FDA approval.

Several panelists said they were also reassured by an extraordinary exchange at the meeting in which an FDA official requested — and Amylyx affirmed — that the company would voluntarily pull its drug from the market if a large, ongoing study doesn’t confirm its benefit.

That 600-patient study is expected to report results in 2024. But experts have pointed to the many potential problems with such an informal commitment. The FDA and the company could disagree on whether the final data supports the drug; or a future company that acquires the drug may not feel bound by Amylyx’s pledge.

The company’s powder-based drug is a combination of two older ingredients: a prescription medication for liver disorders and a dietary supplement associated with traditional Chinese medicine. Cambridge, Massachusetts-based Amylyx has patented the combination and says the chemicals work together to shield cells from premature death.

Some ALS patients already take both drugs separately. But FDA approval is expected to compel insurers to cover the treatment, raising questions about its price.

Amylyx did not immediately announce the drug’s price after the FDA announcement on Thursday.

“The ALS community has proven that our advocacy can impact decisions that are being made about our health,” said Larry Falivena, an ALS Association board member who was diagnosed with the disease in 2017, in an emailed statement. The group invested $2.2 million in Amylyx’s early research and stands to recoup $3.3 million from the drug’s profits.