Many people reach for melatonin supplements as a seemingly harmless solution for a restless night. Marketed as a natural sleep aid, it’s a go-to for those struggling with insomnia. However, a new study suggests that long-term use of this popular supplement may carry significant health risks, particularly for the heart.

The study’s findings were presented this month at the American Heart Association’s Scientific Sessions 2025.

Melatonin is a hormone naturally produced by the pineal gland of the brain. Its primary function is to regulate the body's sleep-wake cycle, also known as the circadian rhythm. When darkness falls, melatonin levels rise, signaling to your body that it's time to sleep. As daylight returns, levels drop, helping you wake up.

Synthetic versions of melatonin are sold over-the-counter in many countries, including the United States. These supplements are widely used to combat sleep issues like insomnia, which is the difficulty of falling or staying asleep, and to manage jet lag.

"Melatonin supplements are promoted as a safe and natural sleep aid, but the evidence for their long-term cardiovascular safety has been limited," explains Harneet Walia, M.D., medical director of sleep medicine at Baptist Health Miami Cardiac & Vascular Institute and chief of clinical transformation for Baptist Health Medical Group.  "The goal of this study was to examine whether prolonged melatonin use might alter the risk of heart failure, specifically in individuals already dealing with chronic insomnia."

It's important to note that in the U.S., the Food and Drug Administration (FDA) does not regulate over-the-counter supplements in the same way it does prescription drugs. This lack of regulation means that the strength and purity of melatonin products can vary significantly from one brand to another.

A New Study Raises Concerns

While melatonin is often perceived as a safe, short-term sleep solution, there has been a lack of data on its long-term safety, especially concerning cardiovascular health. This gap in knowledge prompted researchers to investigate a potential link.

The preliminary study analyzed five years of electronic health records from more than 130,000 adults from the TriNetX Global Research Network, a large international database. Researchers focused on adults with chronic insomnia who had used melatonin for one year or more.

This "melatonin group" was then compared to a "non-melatonin group"—a matched set of individuals with insomnia who had no record of melatonin use. To ensure the focus was on new health issues, individuals who had a prior diagnosis of heart failure or were prescribed other sleep medications were excluded from the analysis.

Key Findings: Melatonin and Heart Failure Risk

The results of the study revealed an association between long-term melatonin use and adverse cardiovascular events. The main analysis found that adults with insomnia who used melatonin for 12 months or longer had an approximately 90 percent higher chance of developing heart failure over a five-year period, compared to those who did not use the supplement.

Heart failure is a serious condition where the heart muscle doesn't pump blood as well as it should. When this happens, the body's organs do not receive enough oxygen-rich blood to function properly. It affects millions of adults and is a leading cause of hospitalization.

A secondary analysis painted an even more concerning picture. The study found that individuals in the melatonin group were:

• Nearly 3.5 times as likely to be hospitalized for heart failure.

• Nearly twice as likely to die from any cause during the five-year study period.

"These findings are significant and suggest a potential red flag that we must investigate further," Dr. Walia said. "An association of this magnitude warrants a closer look at the prescribing and over-the-counter use of melatonin for an extended duration."

Understanding the Study's Limitations

As with any research, it is crucial to consider the study's limitations. The data came from a database that includes countries where melatonin requires a prescription (like the United Kingdom) and countries where it is sold over-the-counter (like the United States).

Because the study relied on electronic health records to identify melatonin users, it could not account for individuals in the U.S. who purchased it without a prescription. These individuals would have been mistakenly placed in the non-melatonin group, which could impact the accuracy of the findings.

"The way melatonin use was documented is a key limitation.” cautions Dr. Walia. “We could only identify users based on medication entries in their health records. This means people taking it as an over-the-counter supplement may have been misclassified. However, the consistent signal across multiple analyses strengthens the need for more controlled, prospective studies."

What Should Consumers Do?

This study does not prove that melatonin causes heart failure, but it does highlight a strong association that calls for caution and further research. It serves as a powerful reminder that "natural" does not always mean "risk-free," especially with long-term use.

If you are using melatonin to manage sleep problems, it is important to speak with your doctor. This is particularly true if you have been using it for an extended period or if you have underlying health conditions.

Your healthcare provider can help you weigh the potential benefits against the risks and explore other evidence-based strategies for improving sleep. These can include cognitive behavioral therapy for insomnia (CBT-I), improving sleep hygiene, and addressing any other medical issues that might be disrupting your rest.

"This research should open a dialogue between patients and their healthcare providers about the appropriateness of long-term melatonin use — and encourage a discussion about alternative, well-established treatments for insomnia," advises Dr. Walia.