Melatonin has long been the sleepy-time staple tucked beside a phone, a glass of water, and maybe a book that never gets finished. But a large preliminary analysis is now raising a sharper question about the supplement many people take without much thought.
Researchers who reviewed 5 years of health records from more than 130,000 adults with insomnia found that long-term melatonin use was associated with a higher risk of heart failure diagnosis, heart failure hospitalization, and death from any cause. The study does not prove melatonin caused those outcomes. Still, it suggests that taking it night after night for a year or longer deserves more careful attention.
A warning sign, not a verdict
The research was presented at the American Heart Association’s Scientific Sessions 2025 and remains preliminary, meaning it has not yet gone through full peer review as a journal article. That matters because conference abstracts can point to important signals, but they are not the final word.
Lead author Ekenedilichukwu Nnadi, M.D., said, “Melatonin supplements may not be as harmless as commonly assumed.” That is a cautious statement, not a panic button, but it lands hard because melatonin is so widely used as a “natural” sleep aid.
What researchers found
The analysis included 130,828 adults with chronic insomnia. Of those, 65,414 had melatonin recorded in their electronic health records for at least 12 months, while a matched comparison group had insomnia but no melatonin recorded.
Over 5 years, people in the long-term melatonin group had about a 90 percent higher chance of a new heart failure diagnosis compared with matched non-users. The actual rates were 4.6 percent versus 2.7 percent, which is a smaller-looking gap on paper, but still meaningful when millions of people may be reaching for the same bottle.
Hospital visits and death rates also rose
The secondary results were also striking. Participants with long-term melatonin use were nearly 3.5 times as likely to be hospitalized for heart failure, with rates of 19.0 percent compared with 6.6 percent in the non-melatonin group.
Deaths from any cause were also higher in the melatonin group. Researchers reported 7.8 percent compared with 4.3 percent over the same 5-year period, which is why the findings are being treated as a safety signal that needs more study.
Why the supplement label matters
Melatonin is a hormone naturally produced by the pineal gland, and it helps regulate the body’s sleep-wake cycle. Darkness usually pushes levels up, while daylight brings them down.
In practical terms, a supplement is meant to nudge that internal clock. That can be useful for jet lag or short-term sleep timing problems, but chronic insomnia is a different story, especially when someone is using the same product for months or years without medical follow-up.
In the United States, melatonin is sold as a dietary supplement. The FDA says it does not approve dietary supplements before they are marketed, and manufacturers generally carry the first responsibility for product safety and labeling compliance.
The big limitation
Here is the tricky part. The researchers did not directly ask every participant what they actually took, how much they took, or whether they bought melatonin over the counter.
That means some people in the “non-melatonin” group may have been using it without a prescription or without it appearing in their medical records. In countries like the United Kingdom, melatonin is prescription-only, but in the United States, it can be bought at a pharmacy, grocery store, or online with no doctor involved.
The researchers also lacked some details that could matter a lot, including insomnia severity and certain psychiatric conditions. Poor sleep, anxiety, depression, and other sleep medications may all be connected to heart risk, which makes it difficult to separate the supplement from the health profile of the people taking it.
Experts urge caution
Carlos Egea, president of the Spanish Federation of Sleep Medicine Societies, noted that the study is observational and cannot establish causality. Still, he said the findings “challenge the perception of melatonin as a benign chronic therapy.”
That is probably the most sensible takeaway. The study does not say every person who has used melatonin is in danger, and it does not change medical guidance on its own. But it does push back against the casual idea that “natural” always means risk-free.
What users should keep in mind
The National Center for Complementary and Integrative Health says short-term use of melatonin appears safe for most people, but information on long-term safety is lacking. It also notes that some melatonin products may not contain what the label says they contain.
That can be a real-world problem. A gummy that looks harmless on the kitchen counter is still affecting the body’s hormone signaling, and the dose on the label may not tell the whole story.
People taking medications, especially blood thinners, or those with epilepsy, pregnancy, breastfeeding, dementia, or complex health conditions should speak with a health care provider before using melatonin. That advice may sound familiar, but with sleep aids, it is easy to skip.
Sleep trouble needs a longer look
Chronic insomnia is not just an annoying night or two of tossing around. It can affect mood, work, driving, appetite, blood pressure, and the rhythm of everyday life.
For chronic insomnia, the American College of Physicians recommends cognitive behavioral therapy for insomnia as an initial treatment. That does not fit neatly into a tiny bottle, but it aims at the habits, thoughts, schedules, and patterns that keep sleep from settling in.
So, what should readers do tonight? Not panic. But if melatonin has become a nightly routine for months on end, especially without medical guidance, it may be time to ask a doctor whether it is still the right tool.
The press release was published on the American Heart Association Newsroom.
