Long-term use of melatonin, a common sleep supplement, may be linked to hospitalization and even death from heart failure, a large new study warns.
Melatonin is a hormone produced by the body to regulate the sleep-wake cycle, and synthetic versions are commonly prescribed as medications to treat insomnia and jet lag.
It can be purchased over the counter in many countries, including the United States.
Because over-the-counter supplements are not regulated, different brands of melatonin can vary greatly in strength and purity and therefore have different long-term effects on the body.
To understand the risks of taking supplements, researchers reviewed the five-year health records of 130,000 adults with insomnia who had taken melatonin for at least a year and compared them with their peers who also had insomnia but had never taken melatonin.
The results showed that patients who used melatonin for more than 12 months were approximately 90% more likely to develop heart failure over a five-year period compared to patients who did not use melatonin.
“Melatonin supplements are widely known as a safe and ‘natural’ option to support better sleep, so it was surprising to see consistent and significant increases in serious health outcomes even after taking into account many other risk factors,” said study author Ekenedilichukwu Nnadi.
Heart failure occurs when the body is unable to supply enough oxygenated blood to the body’s organs to allow them to function properly. It can be fatal.
The new study also found a similar risk of heart failure among people who received at least two prescriptions for melatonin 90 days apart.
Patients who took melatonin were 3.5 times more likely to be hospitalized for heart failure compared to non-users, according to a study that has not yet been peer-reviewed and published in the American Heart Association’s 2025 Heart Disease and Stroke Statistics.
“We were surprised to learn that, at least in the United States, doctors are prescribing melatonin for insomnia and having patients use it for more than 365 days because melatonin is not suitable for treating insomnia,” said Marie-Pierre St-Onge, another author of the study.
“It is important to keep in mind that in the United States, melatonin can be taken as a general supplement and should not be taken chronically without appropriate indications.”
Researchers cautioned that the study had limitations, including a lack of information about the severity of insomnia and the presence of other mental disorders among participants.
“The association we found raises safety concerns for this widely used supplement, but our study cannot demonstrate direct causality,” said Dr. Nnadi. “This means that more research is needed to test the safety of melatonin for the heart.”
