Taking melatonin to fall asleep might come with an unexpected side effect, according to new research from the American Heart Association.

A review of health records from more than 130,000 adults found that people who used melatonin for a year or longer were significantly more likely to develop heart failure, be hospitalized for it, or die from any cause within five years.

The findings were presented on Monday at the association’s Scientific Sessions 2025 in New Orleans.

“Melatonin supplements may not be as harmless as commonly assumed,” Dr. Ekenedilichukwu Nnadi, the study’s lead author, said in a statement. “If our study is confirmed, this could affect how doctors counsel patients about sleep aids.”