One of the most popular supplements sold in the United States may have an unintended side effect, research suggests.
Often touted as a safe sleep aid, melatonin is a hormonal supplement that many people can buy over the counter and take without much thought.
But preliminary research has some scientists concerned about what happens when taking the supplement becomes a long-term habit.
A 2025 analysis of adults with insomnia linked prescribing melatonin for more than a year to a higher risk of heart problems.
Among more than 130,000 adults across several countries, those who were prescribed melatonin long-term were at greater risk of heart failure and death over the next five years than those who were not prescribed it.
People who were prescribed melatonin for more than a year were found to have an 89% higher risk of heart failure over five years and were about twice as likely to die from any cause.
Watch the clip below for a summary of the results:
The research, which has not yet been peer-reviewed, was presented in November 2025 at the American Heart Association Scientific Sessions.
The results are preliminary. They do not prove that melatonin – the fourth most consumed natural product by adults in the United States – has dangerous repercussions.
But they suggest that long-term use requires further study.
In April 2026, Saudi Arabia’s pharmaceutical regulator issued a formal safety signal on melatonin and heart failure, after reviewing global case reports alongside the study’s findings, concluding that the evidence so far “suggests a causal association.” This isn’t a ban or a new warning label, but it’s a sign that regulators are starting to take this possibility seriously.
However, melatonin is generally considered safe and well-tolerated for short-term use by people who are not pregnant or breastfeeding. This means approximately 1-2 months.
There are few studies on the effects after this time, a situation that some researchers believe should be addressed, especially as the supplement grows in popularity.
“Melatonin supplements may not be as harmless as commonly thought,” said medical scientist Ekenedilichukwu Nnadi of SUNY Downstate/Kings County Primary Care in New York.
A melatonin supplement mimics a hormone naturally produced by the brain to help keep the body’s internal clock ticking. Taking this substitute at the end of the day may help some people fall and stay asleep.
In the United States and many other countries, melatonin supplements are available over-the-counter, meaning patients can take them without medical advice or supervision regarding dosage or duration of use.
Although some studies suggest that long-term use of melatonin is safe, in-depth research is lacking.
In a recent analysis, Nnadi and colleagues examined electronic health records of adults in the United States and several other countries, including the United Kingdom, where melatonin is available only by prescription.
A secondary analysis found that those who took melatonin for more than a year were nearly 3.5 times more likely to be hospitalized for heart failure than those who did not take it.
Additionally, the risk of dying from any cause increased from 4.3 percent to 7.8 percent between groups.
“Melatonin supplements are widely considered a safe and ‘natural’ option to promote better sleep,” Nnadi said.
“It was therefore striking to see such a consistent and significant increase in serious health problems, even after accounting for many other risk factors.”
The results are concerning, but they must be interpreted with caution. The study methodology presents a major limitation.
Participants were not asked about their melatonin consumption.
Instead, prescription records were used to estimate who was taking the supplement.
This means that the control group, composed of those who were not prescribed melatonin, may have included people in the United States who purchased over-the-counter melatonin and took it without a prescription.
Carlos Egea, president of the Spanish Federation of Sleep Medicine Societies, who was not involved in the study, noted this caution in an expert reaction to the research.
However, he said such associations should be taken seriously.
“These results challenge the perception of melatonin as a benign chronic treatment and only highlight the need for a prospective trial with a control group to clarify its safety profile,” explained Egea.
Related: Study Links 5 Sleep Subtypes to Distinct Health and Lifestyle Patterns
Even in the short term, melatonin can have disadvantages that many users may not be aware of.
For example, a series of non-fatal overdoses among children in Australia has raised questions about the supplement’s safety profile for certain age groups.
Melatonin products may be based on a natural hormone, but that doesn’t mean they’re risk-free.
“If our study is confirmed, it could affect how doctors advise their patients about sleeping pills,” Nnadi said.
The results were presented at the American Heart Association Scientific Sessions in 2025.
This article was fact-checked by Rebecca Dyer and edited by Rebecca Dyer. Although we are proud of our process, we are only human. If you spot an error, please let us know.
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