Could Melatonin Be Silently Harming Your Heart?

Marketed as nature’s sleep switch, melatonin has become a nightly habit for millions. But new research presented this week at the American Heart Association’s Scientific Sessions 2025, suggests the supplement may do more than quiet the mind — it could also trouble the heart.

In the review of more than 130,000 adults with insomnia, long-term melatonin use (for a year or more) was linked with a nearly doubled risk of developing heart failure, more than triple the risk of hospitalization for heart failure, and nearly twice the risk of death over five years.

“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,” said Ekenedilichukwu Nnadi, study lead, in a press release.

Why Melatonin May Strain the Heart

Produced by the brain’s pineal gland, melatonin helps govern the circadian rhythm — rising at night to signal sleep and falling with daylight. Synthetic versions of the hormone, identical to the body’s own, are sold over the counter in much of the world, where they’re marketed as a “natural” sleep remedy.

Because supplements are not regulated as pharmaceuticals, however, their actual potency and purity can vary widely across brands and formulations.

”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 U.S., is not indicated for the treatment of insomnia,” said Marie-Pierre St-Onge, a sleep researcher at Columbia University.

Read More: Does Melatonin Cause Dementia?

Tracking the Heart Risks of Melatonin

To explore melatonin’s long-term effects, Nnadi’s team examined electronic health records from 130,828 adults diagnosed with insomnia — average age 55.7 years, about 61 percent women — using the TriNetX Global Research Network, a massive international database of anonymized medical data.

Roughly 65,000 participants had used melatonin for at least a year and formed the “melatonin group.” Another 65,000 who had never been prescribed melatonin served as a matched control group, adjusted across 40 factors including age, sex, body mass index, race, blood pressure, and medications for heart and nervous system diseases. People already diagnosed with heart failure, according to the American Heart Association, or prescribed other sleep aids, such as benzodiazepines, were excluded.

Over a five-year period, clear patterns emerged. Long-term melatonin users had about a 90 percent higher chance of developing heart failure compared with non-users. When the analysis was tightened to include only those who had filled at least two prescriptions 90 days apart, the risk remained nearly identical — 82 percent higher.

The gaps widened with more severe outcomes. Melatonin users were 3.5 times more likely to be hospitalized for heart failure (19 percent vs. 6.6 percent) and nearly twice as likely to die from any cause (7.8 percent vs. 4.3 percent) within the five-year window.

Rethinking a Natural Nightly Habit

While these results were presented at the American Heart Association’s Scientific Sessions 2025, the results are still preliminary — but they hint at a bigger story. The researchers stress that the study doesn’t prove melatonin harms the heart, only that long-term users seem to face higher risks.

Because the supplement is sold over the counter, countless people who take it nightly never show up in medical databases, making the real picture harder to see.

“Worse insomnia, depression/anxiety or the use of other sleep-enhancing medicines might be linked to both melatonin use and heart risk,” Nnadi said in the press release. “Also, while the association we found raises safety concerns about the widely used supplement, our study cannot prove a direct cause-and-effect relationship. This means more research is needed to test melatonin’s safety for the heart.”

This article is not offering medical advice and should be used for informational purposes only.

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Article Sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:

• This article references information presented in the American Heart Association Scientific Sessions 2025 News Release Abstract.
• This article references information from the American Heart Association: What is Heart Failure?