A widely prescribed asthma drug may be linked to serious mental health problems and suicide for some patients, a new study finds. The Food and Drug Administration (FDA) presented preliminary results of a study on the asthma drug Singulair, sold generically as montelukast, for “limited audiences.” The scientific presentation was reviewed by Reuters. The study found that the drug binds to multiple brain receptors important for psychiatric functioning.

According to a Reuters report, Singulair was a blockbuster product when it was launched in 1998. It provided relief in a pill as an alternative to inhalers. In early advertising, the company said that the side effects were so mild that they were “similar to a sugar pill”, while the label stated that any distribution to the brain was “minimal”. Generic versions are still prescribed to millions of adults and children each year.

However, by 2019, thousands of reports of neuropsychiatric episodes, including dozens of suicides, in patients prescribed the drug had accumulated on Internet forums and in the US Food and Drug Administration’s tracking systems. These “adverse event” reports do not prove a causal relationship between a drug and a side effect, but are used by the FDA to determine whether more study is needed about the drug’s risks.

Following analysis, the report and new scientific research prompted the FDA in 2020 to add a “black box” warning to montelukast prescribing labels, flagging serious mental health risks such as suicidal thinking or actions. The agency also convened a group of internal experts around the same time to explore why the drug might trigger neuropsychiatric side effects.

The results of the group’s work were presented to a limited audience at a meeting of the American College of Toxicology in Austin, Texas.

Jessica Oliphant, deputy director of the FDA’s National Center for Toxicological Research, said at the event that laboratory tests have shown that montelukast has “significant binding” to multiple receptors found in the brain. The FDA also said that scientific research shows that montelukast enters the brains of rats.

Oliphant said more study is needed about how the drug accumulates in the nervous system. He added, “These data indicate that montelukast is in the brain regions most likely to be involved in (psychiatric effects).”

When the FDA added the black box, it cited research by Julia Marschelinger and Ludwig Aigner at Austria’s Institute of Molecular Regenerative Medicine. Speaking to Reuters, both scientists said the new data showed that significant amounts of montelukast are present in the brain. He said the receptors involved play a role in regulating mood, impulse control, cognition and sleep, among other functions.

Both scientists said the research does not show whether that binding mechanism has direct harmful effects in individual patients or who is particularly at risk. However, Marschallinger said the new data reinforces reports from people who reported suffering side effects. He added, “It’s definitely something that’s of concern.”

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