DALLAS — Long-term use of melatonin supplements, a popular over-the-counter sleep aid, was associated with an increased risk of heart failure, hospitalization, and death among adults with chronic insomnia, according to preliminary research presented Monday at the American Heart Association’s Scientific Sessions 2025 in New Orleans.
Researchers reviewed five years of electronic health records for more than 130,000 adults with insomnia who had used melatonin for at least one year, the American Heart Association said in a statement. One of the major findings of the analysis showed that adults with insomnia who used melatonin for 12 months or more had about a 90% higher risk of heart failure within five years than non-users.
“Melatonin supplements may not be as harmless as commonly assumed,” said Dr. Ekenedilichukwu Nnadi, lead author of the study and chief resident in internal medicine at SUNY Downstate/Kings County Primary Care in Brooklyn, New York. “If our study is confirmed, this could affect how doctors counsel patients about sleep aids.”
The research also found that participants taking melatonin were 3.5 times more likely to be hospitalized for heart failure compared to those not taking the supplement.
Melatonin is a hormone naturally produced by the pineal gland that regulates the body’s sleep-wake cycle. Synthetic versions are sold over the counter in the United States, but unlike prescription drugs, they are not regulated for purity or dosage consistency.
“I’m surprised that physicians would prescribe melatonin for insomnia and have patients use it for more than 365 days,” said Dr. Marie-Pierre St-Onge, chair of the American Heart Association’s 2025 scientific statement on sleep health and a professor at Columbia University Irving Medical Center, who was not involved in the study. “People should be aware that it should not be taken chronically without a proper indication.”
Researchers emphasized that their findings show an association, not proof of causation, and that additional studies are needed to confirm whether melatonin directly affects cardiovascular health.
“While the association we found raises safety concerns about this widely used supplement, our study cannot prove a direct cause-and-effect relationship,” Dr. Nnadi said. “This means more research is needed to test melatonin’s safety for the heart.”
The study, based on data from the TriNetX Global Research Network, included 130,828 adults with an average age of 55.7 years; about 61% were women. Researchers matched melatonin users and non-users on 40 demographic and medical characteristics, excluding anyone who had previously been diagnosed with heart failure or prescribed other sleep medications.
The findings remain preliminary until published in a peer-reviewed scientific journal.
