A widely used asthma therapy first marketed by Merck (NYSE:MRK) may be associated with severe mental issues, including suicidal thoughts, for some patients, Reuters reported Friday, citing a scientific presentation.

According to researchers, the drug branded as Singulair and is now available as montelukast in generics gets attached to multiple brain receptors central to psychiatric functioning.

Launched in 1998, Singulair reached blockbuster status for Merck (NYSE:MRK) before its generic versions entered the market.

However, thousands of cases of neuropsychiatric episodes, including suicides in patients who used montelukast, had piled up in internet forums and the FDA databases by 2019.

After adding a black box label in 2020 to montelukast to indicate the risk, the FDA convened a group of experts to identify its link to neuropsychiatric events.

This Wednesday, the group shared their preliminary findings at the American College of Toxicology meeting in Austin, Texas.

"These data indicate that montelukast is highest in brain regions known to be involved in (psychiatric effects)," said Jessica Oliphant, a deputy director at FDA's National Center for Toxicological Research, at the event.

In 2023, Reuters reported that Merck (MRK) is facing lawsuits alleging that the company knew from its early research that montelukast was linked to brain issues.

A Merck (MRK) spokesperson declined to respond to the latest report while its spinoff, Organon (NYSE:OGN), which currently markets Singulair, vouched for the drug's safety profile.

"The product label for Singulair contains appropriate information regarding Singulair benefits, risks, and reported adverse reactions," the company added.