Melatonin is one of the most popular over-the-counter supplements for sleep in the United States; an estimated six million Americans take it to help them fall asleep faster or stay asleep longer.

But a new study presented at the American Heart Association (AHA) Scientific Sessions 2025 suggests that taking melatonin long-term may pose risks.

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Researchers found that adults with insomnia who used melatonin for at least a year were significantly more likely to develop or require hospitalization for heart failure or die from any cause over a five-year period compared with similar adults who did not take melatonin.

In people with heart failure, the heart is not pumping as well as it should, and as a result the body may not be getting sufficient oxygen.

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“Melatonin supplements may not be as harmless as commonly assumed,” says lead study author Ekenedilichukwu Nnadi, MD, chief resident in internal medicine at Kings County Hospital and Downstate Health Sciences University in Brooklyn, New York.

If other studies confirm these findings it could affect the risk-benefit discussion that doctors have with their patients about the sleep aid, adds Dr. Nnadi.

Melatonin Use Was Linked to a 90 Percent Increase in Heart Failure

To investigate the effects of long-term melatonin use, study researchers gathered health records from a large international database of over 130,000 adults with insomnia and no previous diagnosis of heart failure. They compared people who had used melatonin long-term (defined as longer than a year) with a group with similar characteristics who had never used melatonin.

An analysis of these two groups found:

People who took melatonin long-term had about a 90 percent higher chance of developing heart failure over a five-year follow up compared with people who didn’t take it.When researchers analyzed people who had at least two melatonin prescriptions filled at least 90 days apart (melatonin is only available by prescription in the United Kingdom), the result was similar: an 82 percent higher risk of heart failure.People taking melatonin long-term were nearly 3.5 times as likely to be hospitalized for heart failure compared with people not taking it (19 percent of participants versus 6.6 percent, respectively).People in the melatonin group were nearly twice as likely to die from any cause compared with the nonmelatonin group (7.8 percent versus 4.3 percent, respectively) over the five-year period.

The findings suggest that more studies need to look at melatonin’s long-term effects on the heart — particularly in people who already have other heart health risk factors, Nnadi says. “It’s a reminder that even over-the-counter supplements can have real physiological consequences,” he adds.

The Study Has Limitations

Tamara Horwich, MD, a cardiologist and clinical professor of medicine at the David Geffen School of Medicine at UCLA in Los Angeles, says that although the study is interesting, it can’t prove that melatonin caused the increased heart health risks.

From the data alone, it’s hard to know if melatonin itself is responsible for the increased risk of heart failure and death, says Dr. Horwich, who wasn’t involved in the research.

It could be that melatonin use is tied to other factors that can make heart failure and early death more likely, such as lower income, lower education, or mental health conditions, she says.

“There are actually studies which have suggested that melatonin may have beneficial effects on the cardiovascular system, including protection against heart failure and cardiomyopathy,” Horwich adds.

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Nnadi acknowledges that his study doesn’t prove melatonin raises risks, but “it raises an important signal that we have to consider,” he says.

Melatonin Is Cheap and Easy to Get

Melatonin is a hormone naturally produced in the body by the pineal gland, and it helps regulate the body’s sleep-wake cycle. Melatonin levels increase during darkness and decrease during daylight. Synthetic versions of the hormone are often used to treat jet lag and insomnia, which is difficulty falling asleep, staying asleep, or both.

Nnadi says the idea for the study grew out of his experience working in an underserved community where access to prescription sleep medications is limited. “Because melatonin is inexpensive and available over the counter, it’s often the only option many of my patients have,” he says.

“We also know that insomnia itself is linked to higher cardiovascular risk. I started wondering whether long-term melatonin use might influence those same pathways — either in a protective or harmful way,” says Nnadi.

Melatonin Supplements Can Affect the Whole Body

In the United States, melatonin is sold as an over-the-counter dietary supplement and is not regulated by the U.S. Food and Drug Administration (FDA). This means its strength and purity can vary widely by brand.

Using melatonin for short periods is generally considered safe for most adults, says Steven Holfinger, MD, a sleep medicine physician at The Ohio State University Wexner Medical Center in Columbus.

“In the short term, we’ve seen melatonin generally well-tolerated with few short-term side effects — things like dizziness, headache, or daytime drowsiness. But there aren’t enough large, long-term studies to say with certainty that it’s safe,” says Dr. Holfinger, who wasn’t involved in the study.

We do know melatonin affects more than sleep, he says. “Receptors for melatonin are found on cells throughout the body, including blood vessels.”

Melatonin may interact with other medications you may be taking, such as some diabetes and blood pressure medications, says Horwich.

Talk to Your Doctor if You’re Reaching for Melatonin Every Night

Before taking melatonin on a regular basis, discuss it with your healthcare provider.

“Melatonin can be useful for short-term sleep issues or adjusting to jet lag, but it’s not meant to be taken indefinitely without medical guidance. If you’re using melatonin every night, talk to your doctor. There may be better-supported ways to improve sleep, such as optimizing sleep hygiene,” says Nnadi.