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On the face of it, melatonin looks harmless: a small pill, a promise of sleep, an easy purchase off a pharmacy shelf. Many people reach for it nightly and carry on with their lives. But a recent multi-country analysis has raised a troubling question: could habitual melatonin use be nudging some people toward serious heart problems?
Signals from health records
Researchers compiling electronic health records from more than 130,000 adults examined prescriptions for melatonin and tracked outcomes over five years. Those who were prescribed melatonin for longer than a year showed a notably higher incidence of heart failure and an elevated overall mortality rate compared with people who were not prescribed the hormone.
The headline numbers are stark. Long-term prescription correlated with an 89 percent increase in the risk of heart failure within five years. All-cause mortality roughly doubled in that same window — rising from 4.3 percent in the comparison group to 7.8 percent among long-term users. A secondary analysis reported nearly a 3.5-fold greater likelihood of hospitalization for heart failure.
These results were presented at the American Heart Association's Scientific Sessions but have not yet passed through peer review. That matters. Preliminary findings can point toward genuine risk, but they can also reflect confounding factors or gaps in how data were collected.
What the study can — and cannot — tell us
Interpretation is constrained by method. The investigators used prescription records to identify melatonin users. In countries like the United States, where melatonin is widely available over the counter, that approach can miss many consumers who self-medicate without a prescription. In other nations, such as the United Kingdom, melatonin is prescription-only, so records there are more complete. That mismatch introduces uncertainty: some people counted as "non-users" in the dataset might in fact have been taking over-the-counter melatonin.
Carlos Egea, president of the Spanish Federation of Sleep Medicine Societies and not involved in the study, cautioned that the associations are not causal proof. Still, he emphasized the importance of the signal: "These data challenge the perception of melatonin as a benign chronic therapy and underline the need for controlled prospective trials."
Medical scientist Ekenedilichukwu Nnadi, who led the analysis, echoed that caution while stressing the consistent pattern across multiple datasets. "Melatonin supplements are widely thought of as a safe and ‘natural’ option to support better sleep," Nnadi said. "It was striking to see consistent increases in serious cardiovascular outcomes even after adjusting for known risk factors."
Biological plausibility and gaps
Melatonin is not an herbal tonic; it is a hormone produced by the pineal gland that helps regulate circadian rhythms. Taken at night, it can shift the timing of sleep. For short courses — a few days to a couple of months — many studies show reasonable safety for most adults who are not pregnant or breastfeeding. But the long-term endocrine effects of supplemental melatonin are poorly characterized.
Could persistent melatonin intake alter cardiovascular physiology? It’s possible. Melatonin interacts with receptors throughout the body, and its effects on blood pressure, heart rate, metabolism, and inflammatory pathways are complex. Some animal and small human studies suggest potential cardioprotective properties under certain conditions, while others hint at adverse effects when exposure is prolonged or dosed inappropriately. The current analysis does not settle those mechanistic questions.
Practical takeaways for clinicians and users
For now, clinical guidelines remain unchanged. Short-term melatonin use for circadian rhythm disorders or transient insomnia is generally considered acceptable for many adults. But the new findings argue for prudence: physicians and pharmacists should ask about melatonin use, advise on limiting duration where appropriate, and consider alternative, evidence-based sleep interventions such as cognitive behavioral therapy for insomnia (CBT-I).
Parents should also be vigilant. Reports of non-fatal pediatric overdoses in some countries have highlighted risks when children gain access to dosing meant for adults. Melatonin is a hormone, not an innocuous candy.
Expert Insight
"The correlation here is a warning flag, not a verdict," says Dr. Laura Mitchell, a cardiologist and clinical researcher who studies sleep-cardiac interactions. "We need randomized trials that monitor cardiac markers and imaging over time, and we need better tracking of over-the-counter use. Until then, I counsel patients to treat melatonin like any other medication: use the lowest effective dose for the shortest necessary period and check in regularly with a clinician."
Conclusion
This evolving picture does not mean melatonin is definitively harmful in all long-term users. But it does shift the risk-benefit conversation. A supplement that many assume is harmless deserves rigorous, prospective study—especially given how common its use has become. Clinicians should document sleep-aid use, researchers should prioritize trials that can test causality, and consumers should approach nightly melatonin with more awareness than convenience.
Source: sciencealert
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