PFor many it is a harmless aid to sleep better. An easy-to-find, “natural” tablet, often used for months or years. Yet, one new research presented in the United States invites us to reconsider the prolonged use of melatonin, especially in those suffering from chronic insomnia. The study was presented at American Heart Association Scientific Sessions 2025 and analyzed the health data of over 130 thousand adults with insomnia. The results, still preliminary, suggest an association between long-term intake of melatonin and a increased risk of heart failurehospital admissions and all-cause mortality.
Melatonin: what the study says
The researchers examined five years of electronic medical records of patients with chronic insomnia, comparing those who had taken melatonin for at least a year with those who had never used it. All participants had no previous diagnoses of heart failure and were not taking any other sleep medications.
The numbers are the most striking: those who had used melatonin long term showed a risk of heart failure approximately 90% higher compared to non-users; the risk of hospitalization for heart failure was over three times greater; all-cause mortality resulted almost doubled during the observation period. Similar results also emerged in a more restrictive analysis, which included only those who had received at least two melatonin prescriptions spaced over time (relevant in countries, such as the United Kingdom, where melatonin must be prescribed).
“It’s not as harmless as you think”
“Melatonin supplements may not be as harmless as commonly believed,” he said ANDkenedilichukwu Nnadilead author of the study and chief resident in internal medicine at SUNY Downstate of New York. “If these findings are confirmed, they could change the way doctors counsel patients about sleep aids.”
In the United States, melatonin is sold as an over-the-counter supplementwithout stringent controls on dosages, purity and quality. This means that different products can have very different concentrations of the same substance.
In Italy, as recommended by Ministry of HealthAnd and of theAIFA, melatonin is available without a medical prescription as a food supplement, but with a maximum dosage of 1 mg per daily dose. Above this threshold it is no longer considered a simple supplement: the formulations from 2 mg prolonged release fall into the category of drugs and require a medical prescription.
Precisely because it is sold as an over-the-counter product, melatonin is often perceived as harmless. But experts remind us that supplements can also have effects on the body, especially if taken for long periods and without medical supervision.
The opinion of the experts
Even those who did not participate in the study urge caution. “I’m surprised that it is prescribed for periods longer than a year,” she observes Marie-Pierre St-Ongeprofessor at Columbia University Irving Medical Centerpresident of the working group ofAmerican Heart Association on sleep and cardiometabolic health. «In the United States, melatonin is not indicated for the treatment of chronic insomnia and it should not be taken for a long time without a real clinical indication».
Warning: further studies are needed
The authors themselves underline the limitations of the study. It is aobservational analysisbased on health data, which does not demonstrate a cause-effect relationship. Factors such as the severity of insomnia, the presence of anxiety or depression or the use of other drugs could influence both the use of melatonin and cardiovascular risk. “More severe insomnia or associated psychological disorders could explain part of the increased risk,” explains Nnadi. “Because of this further studies are needed to clarify safety cardiovascular effects of melatonin”.
Supplements are not harmless
Melatonin remains a fundamental hormone for the sleep-wake rhythm and can play a role in specific situations, such as jet lag or circadian disorders. But this research reinforces a message already known to sleep specialists: supplements are not automatically harmlessespecially if used for a long time and without medical supervision.
While waiting for more in-depth studies and definitive publications, the advice remains the simplest and often overlooked. If sleep doesn’t come, before relying on a “natural” pill, it’s best to talk to your doctor and investigate the true causes of insomnia. Because sleeping well is important, but doing it safely is even more important.
