Melatonin use linked to higher risk of heart failure, study warns

Prolonged use of the common sleep supplement melatonin could be linked to a higher risk of heart failure or death, according to a new large-scale study.

Researchers reviewed five years of health records from more than 130,000 adults with insomnia who had taken melatonin for at least a year and compared them with those who had never used it. They found that long-term melatonin users had about a 90% higher chance of heart failure over five years than non-users, The Independent shares. 

“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.

The study, presented at the American Heart Association’s 2025 Heart Disease and Stroke Statistics, also found that patients with at least two melatonin prescriptions filled 90 days apart were 3.5 times more likely to be hospitalised for heart failure compared to non-users.

“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,” said co-author Marie-Pierre St-Onge. “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 findings come with limitations, including lacking data on the severity of insomnia and other psychiatric conditions.

“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.”

By Sabina Mammadli