A five-year review of the medical records of more than 130,000 adults with insomnia who took 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 improve sleep and treat insomnia, was associated with a higher 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 in the dark and decrease in 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 United States.
In the new study, researchers classified people who took melatonin long-term (with long-term use defined as a year or more recorded in their electronic health records) as part of the melatonin group.
In contrast, those who never had melatonin in their medical records were assigned to the nonmelatonin group.
“Melatonin supplements may not be as harmless as commonly believed,” said Dr. Ekenedilichukwu Nnadi of SUNY Downstate/Kings County Primary Care.
“If our study is confirmed, it could influence how doctors counsel patients about sleeping pills.”
Melatonin supplements are advertised and sold as a safe sleep aid; however, data supporting its long-term cardiovascular safety are lacking, prompting researchers to study whether melatonin use modifies the risk of heart failure, particularly in patients with chronic insomnia.
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 disease affecting 6.7 million adults in the United States, according to the American Heart Association's 2025 Heart Disease and Stroke Statistics.
Using a large international database, the authors analyzed five years of electronic health records of adults with chronic insomnia who had melatonin recorded in their medical records and used them for more than a year.
They were matched with peers in the database who also had insomnia but never had melatonin in their medical records.
People who had previously been diagnosed with heart failure or were prescribed other sleeping pills were excluded from the analysis.
The researchers 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 risk of developing heart failure over five years compared with those who did not use melatonin (4.6% vs. 2.7%, respectively).
The result was similar (82% higher) when the researchers analyzed people who received at least two melatonin prescriptions at least 90 days apart.
In a secondary analysis, the researchers found that participants taking melatonin were nearly 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 nearly twice as likely to die from any cause as those in the non-melatonin group (7.8% vs. 4.3%, respectively) over the 5-year period.
“Melatonin supplements are widely considered a safe and 'natural' option for improving sleep, so it was striking to see such a consistent and significant increase in serious health effects, even after balancing out many other risk factors,” Dr. Nnadi said.
“I'm surprised that doctors are prescribing melatonin for insomnia and forcing patients to use it for more than 365 days, since melatonin, at least in the United States, is not indicated for the treatment of insomnia,” said Dr. Marie-Pierre St. Onge of Columbia University.
“In the US, melatonin can be taken as an over-the-counter supplement, and people should be aware that it should not be taken routinely unless indicated.”
The results will be presented this week at American Heart Association Scientific Sessions 2025.
