Long-term use of melatonin supplements may be linked with a higher risk of heart failure, according to new research — but does that mean people taking it as a sleep aid should stop using it now?

In a review of electronic medical records, thousands of adults who had chronic insomnia and took melatonin for a year or longer had a 90% higher chance of heart failure over the next five years, compared with participants who had the same health factors but didn’t take melatonin. Melatonin users were also more than three times as likely to be hospitalized for heart failure and about twice as likely to die from any cause.

But experts suggest holding off on seeing melatonin as a definite danger. The research had significant limitations, was not designed to prove cause and effect, and contradicts previous studies that indicated potential benefits for heart health.

The research has not yet been peer-reviewed or published in a journal, but it will be presented at the American Heart Association’s Scientific Sessions 2025 meeting, taking place November 7–10.

“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 factors,” said Dr. Ekenedilichukwu Nnadi, lead research author and chief resident in internal medicine at SUNY Downstate/Kings County Primary Care in Brooklyn.

However, “while the association we found raises safety concerns about the widely used supplement, our study cannot prove a direct cause-and-effect relationship,” Nnadi said. “This means more research is needed to test melatonin’s safety for the heart.”

Naturally occurring melatonin in the brain is a hormone produced by the pineal gland in response to darkness to help the body wind down for sleep.

The melatonin in supplements can be extracted from the pineal glands of animals or synthetically produced through a chemical process.

In the United States, because melatonin is sold as a dietary supplement, manufacturers are not subject to the same level of scrutiny as drugs approved by the US Food and Drug Administration. As a result, melatonin supplements may contain significantly more of the active ingredient than advertised or necessary, as well as harmful hidden additives.

Chronic insomnia, experienced by about 10% of the global population, is defined by taking more than 30 minutes to fall asleep or fall back to sleep up to three times a week for more than three months. It can lead to problems with memory, daytime energy, mood, thinking and concentration, work or school performance, and social life.

A doctor can help determine whether insomnia is occurring on its own or due to an underlying factor, such as a medical condition or stressful life circumstance, and recommend appropriate treatment. This may include adjusting sleep routines, therapy for mental or emotional distress, cognitive behavioral therapy for insomnia, medication, or treating an underlying medical condition.

Melatonin use and heart health

Melatonin supplements are often marketed as a safe sleep aid, but there has been insufficient data on their long-term cardiovascular safety, the authors said.

The research team assessed more than 130,000 adults with health records in the TriNetX Global Research Network, a large international electronic database. Participants were about 55 years old on average, and 61.4% were women. Those with documented melatonin use for more than a year were classified as the melatonin group, while those without any record of melatonin use formed the non-melatonin group.

These factors introduce several important limitations. The database includes patients from countries where melatonin requires a prescription, such as the United Kingdom, as well as countries like the United States where it does not. This means some people in the non-melatonin group may have been using the supplement without it appearing in their medical records.

The researchers also lacked details on the severity of participants’ insomnia and whether they had mental health conditions, both of which can influence melatonin use and cardiovascular risk.

Insomnia itself has been associated with a higher risk of heart attack or stroke. Disrupted circadian rhythms — in which melatonin plays a key role — and insufficient sleep have also been linked to an increased risk of cardiovascular problems, including heart failure.

Additional limitations include the lack of information on dosage. Industry representatives note that decades of consumer experience and multiple clinical studies suggest low-dose, short-term melatonin use is generally safe for healthy adults when used as directed.

The findings challenge previous research, including analyses that found melatonin supplementation improved quality of life and cardiac function in patients with heart failure.

Melatonin is also an antioxidant, which helps protect DNA from oxidative stress — an imbalance between free radicals and antioxidants in the body.

Before you take sleep aids

Many people turn to melatonin as a short- or long-term solution for sleep problems. However, the supplement has been linked to side effects such as headaches, nausea, dizziness, drowsiness, stomach pain, confusion or disorientation, tremors, low blood pressure, irritability, mild anxiety and depression.

Before using supplements, experts advise speaking with a doctor to obtain a proper diagnosis for sleep difficulties and discuss appropriate treatment options. Melatonin should not be taken chronically without a clear medical indication.

Healthy sleep hygiene includes limiting light exposure and screen time, as well as avoiding food and alcohol in the hours before bed. The bedroom should be dark, cool and quiet.

If you choose to use melatonin, pharmaceutical-grade products are preferred. Look for supplements that have been independently tested and verified for quality and dosage accuracy.

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