Copyright independent
Prolonged use of the common sleep supplement melatonin could be linked to hospitalisation for heart failure, or even death, a new large-scale study warns. Melatonin is a hormone produced by the body to regulate our sleep-wake cycle, and a synthetic version is commonly prescribed as a pill to combat insomnia and jet lag. It is available over the counter in many countries, including the US. Since over-the-counter supplements aren’t regulated, different melatonin brands can vary significantly in strength and purity and, thus, have different long-term effects on the body. To understand the risks of taking the supplement, researchers reviewed five years of health records of over 130,000 adults with insomnia who had taken melatonin for at least a year and compared them with peers who also suffered from insomnia but had never taken melatonin. They found that patients who used melatonin for 12 months or more had about a 90 per cent higher chance of heart failure over five years compared to non-users. “Melatonin supplements are widely thought of as a safe and ‘natural’ option to support better sleep, so it was striking to see such consistent and significant increases in serious health outcomes, even after balancing for many other risk factors,” study author Ekenedilichukwu Nnadi said. Heart failure occurs when it is unable to pump enough oxygenated blood to the body’s organs for them to function properly. It can be fatal. The new study also found a similar risk of heart failure among people who had at least two melatonin prescriptions filled 90 days apart. Patients who took melatonin were 3.5 times more likely to be hospitalised for heart failure compared to non-users, according to the yet-to-be peer-reviewed study presented at the American Heart Association’s 2025 Heart Disease and Stroke Statistics. “I’m surprised that physicians would prescribe melatonin for insomnia and have patients use it for more than 365 days, since melatonin, at least in the US, is not indicated for the treatment of insomnia,” Marie-Pierre St-Onge, another author of the study, said. “In the US, melatonin can be taken as an over-the-counter supplement, and people should be aware that it should not be taken chronically without a proper indication.” The researchers cautioned that their study came with limitations, including that they lacked information on the severity of insomnia and the presence of other psychiatric disorders among the participants. “While the association we found raises safety concerns about the widely used supplement, our study cannot prove a direct cause-and-effect relationship,” Dr Nnadi said. “This means more research is needed to test melatonin’s safety for the heart.”
