Quick Facts

• Adults taking melatonin for chronic insomnia showed 90% higher heart failure risk over five years
• Study tracked 130,828 adults with insomnia, finding 4.6% heart failure rate in melatonin users vs 2.7% in non-users
• Research shows association only, not direct causation, and has not yet undergone peer review

Adults who take melatonin nightly for chronic insomnia face a 90% increased risk of heart failure within five years, according to preliminary research presented at the American Heart Association’s Scientific Sessions 2025.

The study examined 130,828 adults with an average age of 55.7 years. Researchers compared 65,414 people prescribed melatonin for at least one year against an equal number of controls who did not use the supplement.

During the five-year follow-up period, heart failure occurred in 3,021 melatonin users (4.6%) versus 1,797 controls (2.7%). This corresponds to a hazard ratio of 1.89, meaning melatonin users were 89% more likely to develop heart failure.

“Melatonin supplements may not be as harmless as commonly assumed,” said Dr. Ekenedilichukwu Nnadi, the study’s lead author and chief resident in internal medicine at SUNY Downstate/Kings County Primary Care in Brooklyn. “If our study is confirmed, this could affect how doctors counsel patients about sleep aids.”

The research used propensity-score matching to balance participants on demographics, 15 health conditions, heart medications, lab results, vital signs and healthcare use. Melatonin users were also 3.5 times more likely to be hospitalized for heart failure and nearly twice as likely to die from any cause within five years.

Heart failure affects 6.7 million adults in the United States, according to the American Heart Association’s 2025 Heart Disease and Stroke Statistics.

The findings surprised some experts. “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 Dr. Marie-Pierre St-Onge, chair of the writing group for the AHA’s 2025 scientific statement.

Dr. Wendy Troxel, senior scientist at the RAND Corporation, called the study an “important wake-up call” for consumers and healthcare providers. She noted that melatonin is widely promoted and easily purchased over the counter in the United States.

Nnadi emphasized the study’s limitations. “This doesn’t prove that melatonin directly causes heart failure,” he said. The research shows association, not causation, and captures only prescription melatonin use, not over-the-counter purchases.

The Council for Responsible Nutrition responded that the “early, non-peer-reviewed data” cannot establish cause and effect. The organization noted that chronic insomnia itself may contribute to heart problems, “raising more questions than answers.”

The research has not undergone peer review. Abstracts presented at American Heart Association meetings are considered preliminary until published in peer-reviewed journals.

In April 2024, the Council for Responsible Nutrition adopted voluntary guidelines recommending melatonin products include statements such as “For occasional and/or intermittent use only” and advice to consult healthcare professionals for long-term sleep difficulties.

Read more: Take Melatonin Every Night? A New Study Warns Of This Surprising Risk