A large clinical trial has found that a drug commonly used by patients with ALS is not effective at treating the nerve-destroying disease.

The trial enrolled more than 300 patients across 25 sites in Europe and took nearly four years to complete. High-level results released Wednesday show the drug, while generally safe, was no better than a placebo at slowing the disease after a year and a half of treatment.

The study also had a series of secondary goals looking at health measures like lung capacity, survival and the presence of a protein that research suggests is tied to nerve damage. But again, there were no significant differences between the treatment and control groups, according to the research consortium behind the study.

The consortium said it will further analyze the data to understand, among other things, whether there was a difference in how patients with slower- or faster-progressing disease responded to the drug. Those analyses will be presented at a medical meeting in June in Stockholm.

“We are very disappointed to see there was no overall benefit demonstrated,” said Alberto Albanese, the study leader and director of the neurology unit in Italy’s Humanitas Research Hospital. “Given the heterogeneity of ALS, it is important to explore whether the lack of effect was uniform across the whole trial population. Therefore, thorough analysis of subgroups based at intermediate time points is ongoing.”

The study evaluated a chemical known, in short, as TUDCA. In the U.S., it’s approved to treat certain liver diseases, but research indicates that it may also benefit people with neurodegenerative disorders like ALS. It has therefore become commonplace for doctors to recommend and ALS patients to seek out the drug, which can be bought online as a supplement for around $30 per bottle.

To date, the Food and Drug Administration has approved four medicines specifically for ALS. One of them, Relyvrio, is a pairing of TUDCA and another chemical called sodium phenylbutyrate. Relyvrio entered the U.S. market in the fall of 2022 and has generated hundreds of millions of dollars in sales for its developer, Amylyx Pharmaceuticals, which initially priced the medicine at $158,000 for a year’s supply.

By the end of September, nearly 4,000 of the roughly 30,000 ALS patients in the U.S. were on Relyvrio, according to Amylyx’s estimates.

The company may decide in the coming weeks to pull Relyvrio from the market, however, in response to a major setback.

Earlier this month, a large clinical meant to confirm the drug works instead found it no better than a placebo at combating ALS. The results were deeply disappointing to patients and caregivers, many of whom viewed Relyvrio as a source of hope in an area of research rife with failures. Even with available treatments, ALS patients typically live just two to five years following their diagnosis.

Amylyx is still wading through the data. In the meantime, the company has stopped promoting Relyvrio, while doctors have said they will no longer recommend the drug to their patients.

Prior to the study results released Wednesday, some prescribers had planned to switch their Relyvrio-treated patients onto TUDCA alone.

In a statement, the Motor Neurone Disease Association, a U.K.-based charity focused on ALS research and care access, said patients currently taking TUDCA should contact their nurse or neurologist “if they require clinical advice following the release of these findings.”

“This is not the news we hoped for, and we understand that these trial results are extremely disappointing,” the association said.