Long-term melatonin users in the analysis had a 4.6 percent rate of new heart failure over five years, compared with 2.7 percent among matched non-users, roughly a 90 percent higher relative risk. Heart failure hospitalizations were about three and a half times more common in the melatonin group, and death from any cause was nearly twice as common.
The findings were reported by the American Heart Association from a preliminary study presented at its Scientific Sessions in New Orleans in November 2025.
The study is observational and cannot show that melatonin itself caused the extra events. Chronic insomnia is already tied to higher cardiovascular risk, and the analysis could not measure how severe each person's sleep problems were.
How the study was built
Researchers led by Ekenedilichukwu Nnadi, M.D., chief resident in internal medicine at SUNY Downstate/Kings County Primary Care in Brooklyn, New York, pulled records from the TriNetX Global Research Network, a de-identified database of electronic health records. They identified 65,414 adults with an insomnia diagnosis and at least one year of documented melatonin use, then matched them one-to-one with 65,414 insomnia patients who had no record of melatonin use.
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The two groups were balanced on demographics, 15 coexisting conditions, other cardiometabolic medications, laboratory values, vital signs and health care use. Average age was 55.7 years, and 61.4 percent of participants were women. Follow-up ran for five years.
Incident heart failure occurred in 3,021 melatonin users versus 1,797 controls, a hazard ratio of 1.89. Heart failure hospitalizations reached 19.0 percent in the melatonin group and 6.6 percent in the control group, a hazard ratio of 3.44.
All-cause mortality was 7.8 percent versus 4.3 percent, a hazard ratio of 2.09. A sensitivity analysis limited to people with at least two melatonin prescriptions filled 90 or more days apart produced a similar hazard ratio of 1.82.
What the study cannot answer
Because the analysis was built from prescription records, it captures countries where melatonin is prescription-only, such as the United Kingdom, more completely than the United States, where it is sold over the counter. American users who bought melatonin at a pharmacy or grocery store may have been counted as non-users.
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The database also lacked information on insomnia severity, psychiatric conditions and other sleep medications, any of which could push both melatonin use and cardiovascular risk in the same direction.
"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," Nnadi said in the American Heart Association release. The findings have not yet appeared in a peer-reviewed journal.
What this means for people taking it nightly
Melatonin use has climbed sharply in the United States. A JAMA analysis of federal survey data found the share of adults using melatonin rose from 0.4 percent in 1999-2000 to 2.1 percent in 2017-2018, and the National Center for Complementary and Integrative Health reports that sales grew about 150 percent between 2016 and 2020.
Federal health guidance already flags a gap in what is known about long-term use. The NCCIH states that "short-term use of melatonin supplements appears to be safe for most people, but information on the long-term safety of supplementing with melatonin is lacking."
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Board-certified cardiologist Yu-Ming Ni of the MemorialCare Heart and Vascular Institute told Medical News Today that when he does discuss the supplement with patients, "I usually tell my patients to cap it at 1 to 3 mg of melatonin nightly." He also advised anyone with ongoing sleep problems to ask their doctor about a sleep study to rule out sleep apnea.
Anyone currently taking melatonin every night for months at a time should raise it with their primary care doctor before continuing indefinitely, particularly if they already have risk factors for heart disease.
Readers looking for gentler options before reaching for a bottle can start with diet. A recent review of melatonin-rich foods points to tart cherries, pistachios, oats and eggs as everyday sources that raise melatonin naturally, without a nightly pill.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.