A five-year review of health records of more than 130,000 adults with insomnia who used melatonin for at least a year found they were more likely to develop heart failure, need to be hospitalized for the condition or die from any cause.
Long-term use of melatonin supplements, often used to promote sleep and treat insomnia, has been associated with an increased risk of being diagnosed with heart failure. Image credit: Gemini AI.
Melatonin is a hormone that is naturally produced in the body by the pineal gland, and helps regulate the body’s sleep-wake cycle.
Melatonin levels increase during darkness and decrease during the day.
Chemically identical synthetic versions of the hormone are often used to treat insomnia (difficulty falling and/or staying asleep) and jet lag.
Dietary supplements are widely available without a prescription in many countries, including the United States
In a new study, researchers classified people who 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 did not record melatonin anywhere in their medical records were classified as the no-melatonin group.
“Melatonin supplements may not be as harmless as commonly assumed,” said Dr. Ekenedleko Nadi of the State University of New York Primary Care Center in Downstate/Kings County.
“If our study is confirmed, it could impact how doctors advise patients about sleep aids.”
Melatonin supplements are promoted and marketed as a safe sleep aid; However, there are no data proving long-term cardiovascular safety, prompting researchers to examine whether melatonin use changes the risk of heart failure, especially in patients with chronic insomnia.
According to the American Heart Association’s 2025 Heart Disease and Stroke Statistics, heart failure occurs when the heart cannot pump enough oxygen-rich blood to the body’s organs so they can function properly, and it is a common condition that affects 6.7 million adults in the United States.
Using a large international database, researchers reviewed five years of electronic health records of adults with chronic insomnia who recorded melatonin 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 had never had melatonin recorded in their health records.
Subjects were excluded from the analysis if they had previously been diagnosed with heart failure or were 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 a 90% greater chance of developing heart failure over five years compared with matched nonusers (4.6% vs. 2.7%, respectively).
There was a similar result (82% higher) when researchers analyzed people who took at least two melatonin prescriptions at least 90 days apart.
In a secondary analysis, scientists found that participants who took melatonin were about 3.5 times more likely to be hospitalized for heart failure than those not taking melatonin (19.0% vs. 6.6%, respectively).
Participants in the melatonin group were approximately twice as likely to die from any cause than those in the no melatonin group (7.8% versus 4.3%, respectively) over the 5-year period.
“Melatonin supplements are widely believed to be a safe and ‘natural’ option for supporting better sleep, so it was surprising to see such sustained and significant increases in serious health outcomes, even after balancing out many other risk factors,” Dr. Nadi said.
“I’m surprised that doctors are prescribing melatonin to treat insomnia and having patients use it for more than 365 days, since melatonin, at least in the United States, is not indicated for treating insomnia,” said Dr. Marie-Pierre St. Onge of Columbia University.
“In the United States, melatonin can be taken as a dietary supplement without a prescription and people should be aware that it should not be taken chronically without proper counseling.”
The results will be presented this week 2025 American Heart Association Scientific Sessions.