Long-term melatonin in insomnia tied to higher heart-failure risk in AHA analysis

People with chronic insomnia who took melatonin for a year or longer had about a 90 percent higher risk of heart failure over the next five years than similar patients who did not use the hormone, according to a large preliminary analysis released by the American Heart Association on Saturday.

Heart failure occurred in 4.6 percent of the long-term melatonin group and 2.7 percent of the matched comparison group. A tighter check, limited to people who filled at least two melatonin prescriptions 90 days apart, still showed an 82 percent higher risk. Hospitalisation for heart failure was 19.0 percent in the melatonin group and 6.6 percent among non-users, nearly three and a half times as high.

What the study is and is not

The work is observational. It finds an association. It does not prove that melatonin causes heart muscle failure. The AHA summary is explicit on that point. The records come from adults already diagnosed with insomnia. People who stay on a sleep drug for a year differ from people who do not, in ways a matching algorithm cannot fully catch: worse sleep, more depression, more obesity, more undiagnosed heart disease.

Melatonin is sold over the counter in the United States and only by prescription in the United Kingdom. That split matters for the file. Anyone in the U.S. who bought the bottles at a pharmacy without a prescription would be counted as a non-user. The comparison group is therefore mixed. The prescription-only subset, which is cleaner, still showed the 82 percent figure.

A separate 2025 analysis in Circulation, built on more than 130,000 adults with insomnia, reported an 89 percent higher hazard of incident heart failure, a threefold rise in heart-failure admissions and a doubling of all-cause death among regular prescribed users of a year or more. Saturday's AHA release sits in that line of evidence. It is larger in public attention because the association put it out on a news embargo aimed at patients who treat melatonin as a vitamin.

Other data point the other way

Randomised trials tell a different story in a different population. A systematic review in the Journal of Clinical Medicine this spring pooled 14 trials and 1,027 participants. Melatonin improved the change in left-ventricular ejection fraction by a mean 3.95 percentage points, with a clearer signal after coronary bypass. Final ejection fraction, troponin and infarct size did not move with the same consistency. Those trials used short, controlled doses around surgery or acute illness. They are not a five-year study of insomnia patients buying a supermarket bottle.

Low-dose melatonin has also been reported, in animal and small human work, to support coronary vessel growth after infarction. That literature and the AHA file can both be true if the risk sits in long, unmonitored use among people who already sleep badly, and the benefit sits in brief, supervised use after a specific cardiac event. The files have not been designed to test that split.

What a patient can do with this

No regulator has withdrawn melatonin on the basis of these numbers. No guideline has set a hard stop date. The practical reading is narrower. A person who has taken the hormone every night for a year, and who has high blood pressure, diabetes or prior heart disease, now has a published reason to ask a doctor whether the habit should continue. A person who uses it for a week of jet lag does not.

The open question is dose and duration. The AHA analysis treats 12 months as long term. It does not rank 3 milligrams against 10. Until a trial built for that question exists, the extra risk remains a statistical shadow over a product that many households treat as harmless because it is sold next to the toothpaste.