People who take melatonin regularly to help them sleep may be putting their heart health at risk, according to new research presented at the American Heart Association’s Scientific Sessions 2025.
The study found that adults with chronic insomnia who used melatonin for a year or longer were more likely to develop heart failure, be hospitalized for heart problems, or die from any cause than those who did not use the supplement.
Melatonin is a hormone made naturally by the brain to control the body’s sleep-wake cycle. Its production increases in the evening when it gets dark and drops in the morning with daylight. Synthetic melatonin, which mimics this natural hormone, is commonly used to treat insomnia and jet lag.
In the U.S. and many other countries, it can be bought over the counter. However, because supplements are not strictly regulated, the actual dosage and purity of melatonin products can vary widely.
Researchers wanted to understand how long-term use of melatonin might affect the heart. They analyzed health records of more than 130,000 adults with insomnia using data from the TriNetX Global Research Network, an international database of anonymized medical information.
Participants were divided into two groups: those who had taken melatonin for at least one year and those who had never used it. People with previous heart failure or who had taken prescription sleeping pills were excluded.
The results were concerning. Over five years, adults who took melatonin for more than a year had a 90 percent higher risk of developing heart failure compared to those who did not take it (4.6% versus 2.7%).
They were also 3.5 times more likely to be hospitalized for heart failure and nearly twice as likely to die from any cause. Even when the researchers tightened the criteria to include only those who had filled at least two melatonin prescriptions 90 days apart, the results remained similar, showing an 82 percent increased risk.
“Melatonin supplements may not be as harmless as people think,” said Dr. Ekenedilichukwu Nnadi, the study’s lead author and chief resident in internal medicine at SUNY Downstate/Kings County Primary Care in Brooklyn, New York. “If these findings are confirmed, doctors may need to reconsider how they counsel patients about using sleep aids.”
Heart failure occurs when the heart can’t pump enough oxygen-rich blood to meet the body’s needs. According to the American Heart Association, it affects about 6.7 million adults in the United States. While melatonin is often viewed as a “natural” sleep solution, the study highlights the need to better understand its long-term effects on the cardiovascular system.
Dr. Marie-Pierre St-Onge, a sleep expert and chair of the American Heart Association’s 2025 scientific statement on sleep health, said she was surprised that so many patients were taking melatonin for over a year.
“In the U.S., melatonin isn’t approved as a treatment for chronic insomnia,” she said. “People should be aware that it’s not meant for long-term use without medical supervision.”
The researchers pointed out several limitations. The study included participants from countries where melatonin is a prescription drug, like the UK, as well as places where it’s sold over the counter, like the U.S. This means that people who took melatonin without a prescription might not have been recorded in the data.
The team also lacked information about the severity of insomnia, mental health conditions, and lifestyle factors, which could have influenced the results.
Dr. Nnadi cautioned that the study does not prove melatonin causes heart failure—it only shows a strong association. “Worse insomnia, depression, or the use of other medications could play a role,” he explained. “More research is needed to test melatonin’s safety, especially for people using it long term.”
Still, the findings serve as an important reminder that “natural” doesn’t always mean risk-free. Experts recommend that anyone taking melatonin regularly talk to their doctor, review possible side effects, and explore other ways to improve sleep—such as maintaining a regular bedtime, limiting caffeine, and avoiding screens before bed.
If you care about heart health, please read studies about how eating eggs can help reduce heart disease risk, and herbal supplements could harm your heart rhythm.
For more health information, please see recent studies about how drinking milk affects risks of heart disease and cancer, and results showing strawberries could help prevent Alzheimer’s disease.
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