“While this is a difficult moment for the ALS community, we reached this path forward in partnership with the stakeholders who will be impacted and in line with our steadfast commitment to people living with ALS and other neurodegenerative diseases,” Joshua Cohen and Justin Klee, the company’s two CEOs, said in a statement.

The U.S. Food and Drug Administration’s approval of Relyvrio in 2022 generated controversy because it was based on a single clinical trial, and FDA staff and outside experts questioned the drug’s effectiveness. A larger trial whose results were released last month showed the benefit to patients was not even as reliable as a coin toss. The company instantly lost 80 percent of its stock-market value.

About 6,000 people a year in the United States are diagnosed with ALS, often called Lou Gehrig’s disease, which kills by progressively shutting down the body’s ability to move, speak and eventually breathe. There is no known cure.

The company’s decision to voluntarily take Relyvrio off the market is uncommon. At an FDA meeting in 2022, one member of the agency’s expert panel was skeptical about the prospect of pulling the drug from the market if it turned out not to work, saying the FDA underestimated the complexity and likelihood of doing so.

“Frankly, I’m not sure it’s ever taken place, although admittedly in rare cases, manufacturers themselves have made the decision to do so,” Johns Hopkins University internist Caleb Alexander said at the time.

Amylyx made the right decision, Alexander said Thursday. “The case is also a reminder of the standards we have for market access — and the risks of diluting these standards based on factors other than scientific evidence,” he said.

The ALS Association also praised Thursday’s announcement. “We commend Amylyx for pulling Relyvrio off the market, while still ensuring that people living with ALS can access the drug if they believe it is helping them,” the group said in a statement.

Amylyx, founded by Klee and Cohen while they were undergraduates at Brown University, had been an improbable success. The company won FDA approval in 2022 on the strength of a single trial that found Relyvrio slowed the rate of decline, compared with a placebo, in activities like walking and talking. A subsequent data analysis also found that participants who took the drug lived an average of 10 months longer than a control group.

Sales of Relyvrio brought in about $380 million in revenue last year. At one point, Amylyx had a market capitalization exceeding $1 billion.

In most cases, the FDA requires more evidence — two trials that provide compelling data — to approve a drug. But it also exercises a measure of flexibility, taking into account the seriousness of the disease and the adequacy of existing treatments.

On Thursday, Amylyx said it would continue to study the results of its failed larger trial to inform future ALS research. It is continuing to develop another ALS drug, but its leading drug candidate now is for Wolfram syndrome, a hereditary disorder that causes diabetes.