Millions of people swallow their melatonin capsule every evening with complete confidence, convinced that they are using a natural and harmless product to sleep better. However, a large preliminary study presented during the 2025 Scientific Sessions of the American Heart Association has caused confusion. After analyzing the medical records of more than one hundred and thirty thousand adults suffering from chronic insomnia, researchers identified troubling associations between prolonged melatonin consumption and serious cardiovascular problems. These unexpected results could radically transform the way doctors and patients think about this ubiquitous dietary supplement.
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The team of Dr. Ekenedilichukwu Nnadi, chief resident at SUNY Downstate in Brooklyn, used data from the global TriNetX network to compare two groups of insomniacs: those using melatonin for at least a year and those who had never consumed it. The groups were carefully matched on forty factors including age, sex, pre-existing cardiovascular disease, drug treatments, blood pressure and body mass index.
Over a five-year period, the results reveal a worrying picture. Melatonin users have approximately a 90% increased risk of developing heart failure compared to non-users. Concretely, 4.6% of melatonin consumers developed this pathology, compared to 2.7% in the control group.
Hospitalizations tell an even more alarming story. Participants taking melatonin were nearly three and a half times more likely to be hospitalized for heart failure: 19% versus 6.6%. Finally, the all-cause mortality rate is almost twice as high among melatonin users, with 7.8% deaths compared to 4.3%.
A supplement wrongly deemed safe
These findings contrast sharply with the widespread perception of melatonin as a benign substance. In the United States as in France, this food supplement is sold freely without a prescription, reinforcing the illusion of its safety. Its status as a molecule naturally produced by the body also contributes to this blind confidence.
Melatonin is a hormone secreted by the pineal gland that regulates the sleep-wake cycle. Its concentration increases during the night and falls during the day. The synthetic versions sold in pharmacies chemically imitate this endogenous molecule. Officially, they are intended to combat jet lag and temporary sleep disorders, not chronic insomnia.
Doctor Nnadi underlines the seriousness of these results: “ Melatonin supplements are widely considered a safe and natural option for promoting better sleep. It is therefore striking to see such consistent and significant increases in serious health problems, even after accounting for many other risk factors.e. »
Marie-Pierre St-Onge, professor of nutritional medicine at Columbia University and chair of the American Heart Association’s Sleep Health Writing Group, expresses surprise at the long-term use of melatonin: “ I am surprised that doctors prescribe melatonin for insomnia and have their patients use it for more than 365 days, because melatonin, at least in the United States, is not indicated for the treatment of insomnia. »
Significant methodological limitations
Despite its impressive scale, this study has significant flaws that prevent definitive conclusions from being drawn. The major problem is the observational nature of the research: it identifies an association, not direct causation. It is impossible to say with certainty that melatonin causes these heart complications.
The data comes from multiple countries with divergent regulations. In the UK, melatonin requires a prescription, ensuring its presence in medical records. In the United States, however, its status as an over-the-counter supplement means that countless users appear nowhere in official records. These people were therefore wrongly classified in the “no melatonin” group, potentially distorting the results.
Another major gap is the lack of information on the severity of insomnia. The researchers were also unable to assess the presence of associated psychiatric disorders such as depression or anxiety. However, these pathologies are themselves independent cardiovascular risk factors.
Doctor Nnadi openly recognizes these limitations: “ Worsening insomnia, depression or anxiety, or taking other sleeping pills could be linked to both melatonin consumption and heart risk. »
What should you remember for your health?
This preliminary study should not trigger widespread panic, but it calls for caution and nuance. The results must be confirmed by randomized clinical trials, the only ones capable of establishing a cause and effect link. In the meantime, several lessons emerge from this research.
First, melatonin should not be considered a harmless sleeping pill to be consumed indefinitely. Its prolonged use, particularly beyond a year, deserves to be discussed with a healthcare professional. Second, chronic insomnia requires a comprehensive treatment approach rather than a simple nocturnal chemical crutch.
Cognitive-behavioral therapies have demonstrated their effectiveness against insomnia without presenting the potential risks associated with pharmacological treatments. Sleep hygiene, including regular schedules, avoiding screens before bed, and an environment conducive to rest, also provides an essential foundation.
For the six point seven million Americans suffering from heart failure, this study highlights the importance of informing your cardiologist of any dietary supplement intake, even if perceived as harmless. The heart weakened by this pathology could prove particularly vulnerable to the potential adverse effects of substances such as melatonin.
Finally, this research illustrates a larger problem: insufficient regulation of dietary supplements in many countries. The lack of strict supervision regarding their concentration, purity and marketing claims creates an environment where consumers navigate blindly, guided by the erroneous belief that a natural origin guarantees safety.
The coming months will undoubtedly bring clarity when this study is published in a peer-reviewed scientific journal and other teams attempt to reproduce these troubling results. In the meantime, caution remains in order for those considering prolonged use of melatonin.
