U.S. government researchers have found that a widely prescribed asthma drug originally sold by Merck & Co may be linked to serious mental health problems for some patients, according to a scientific presentation reviewed by Reuters.

The researchers found that the drug, sold under the brand name Singulair and generically as montelukast, attaches to multiple brain receptors critical to psychiatric functioning.

But by 2019, thousands of reports of neuropsychiatric episodes, including dozens of suicides, in patients prescribed the drug had piled up on internet forums and in the U.S. Food and Drug Administration’s tracking system. Such “adverse event” reports do not prove a causal link between a medicine and a side effect, but are used by the FDA to determine whether more study of a drug’s risks are warranted.