A review of five years of health records for more than 130,000 adults with insomnia who had used melatonin for at least a year found they were more likely to be diagnosed with heart failure, require hospitalization for the condition or die from any cause.
Long-term use of melatonin supplements, often used to promote sleep and address insomnia, was associated with a higher risk of heart failure diagnosis. Image credit: Gemini AI.
Melatonin is a hormone naturally produced in the body by the pineal gland, and it helps regulate the body’s sleep-wake cycle.
Melatonin levels increase during darkness and decrease during daylight.
Chemically identical synthetic versions of the hormone are often used to treat insomnia (difficulty falling and/or staying asleep) and jet lag.
The supplements are widely available over the counter in many countries, including the U.S.
In a new study, researchers classified people who had used melatonin long-term (with long-term use defined as a year or more documented in their electronic health records) as part of the melatonin group.
In contrast, those who never had melatonin recorded anywhere in their medical records were classified as the non-melatonin group.
“Melatonin supplements may not be as harmless as commonly assumed,” said Dr. Ekenedilichukwu Nnadi from SUNY Downstate/Kings County Primary Care.
“If our study is confirmed, this could affect how doctors counsel patients about sleep aids.”
Melatonin supplements are promoted and marketed as a safe sleep aid; however, data demonstrating their long-term cardiovascular safety are lacking, which prompted the researchers to examine whether melatonin use alters the risk of heart failure, specifically in chronic insomnia patients.
According to the American Heart Association’s 2025 Heart Disease and Stroke Statistics, heart failure occurs when the heart can’t pump enough oxygen-rich blood to the body’s organs for them to function properly and is a common condition that affects 6.7 million adults in the U.S.
Using a large international database, the authors reviewed five years of electronic health records for adults with chronic insomnia who had melatonin recorded in their health records and used it for more than a year.
They were matched with peers in the database who also had insomnia but never had melatonin recorded in their health records.
People were excluded from the analysis if they had previously been diagnosed with heart failure or had been prescribed other sleep medications.
The scientists found that among adults with insomnia, those whose electronic health records indicated long-term melatonin use (12 months or more) had about a 90% higher chance of incident heart failure over five years compared with matched non-users (4.6% vs. 2.7%, respectively).
There was a similar result (82% higher) when the researchers analyzed people who had at least 2 melatonin prescriptions filled at least 90 days apart.
In a secondary analysis, the scientists found that participants taking melatonin were nearly 3.5 times as likely to be hospitalized for heart failure when compared to those not taking melatonin (19.0% vs. 6.6%, respectively).
Participants in the melatonin group were nearly twice as likely to die from any cause than those in the non-melatonin group (7.8% vs. 4.3%, respectively) over the 5-year period.
“Melatonin supplements are widely thought of as a safe and ‘natural’ option to support better sleep, so it was striking to see such consistent and significant increases in serious health outcomes, even after balancing for many other risk factors,” Dr. Nnadi said.
“I’m surprised that physicians would prescribe melatonin for insomnia and have patients use it for more than 365 days, since melatonin, at least in the U.S., is not indicated for the treatment of insomnia,” said Columbia University’s Dr. Marie-Pierre St-Onge.
“In the U.S., melatonin can be taken as an over-the-counter supplement and people should be aware that it should not be taken chronically without a proper indication.”
The findings will be presented this week at the American Heart Association’s Scientific Sessions 2025.
