Melatonin is hugely popular for those who have trouble sleeping: A national survey published in 2022 found that the percentage of participants who used melatonin rose from 0.4% in 1999 to 2.1% in 2018 ― a staggering 425% increase over nearly two decades.

Melatonin, the so-called “sleep hormone,” helps keep your circadian rhythm — your 24-hour internal clock — in sync. Evidence suggests melatonin supplements, which act as a biological “darkness signal” telling your brain and body that it’s time to rest, may help some people fall asleep faster but do little to promote staying asleep.

Melatonin is generally safe for short-term use, but it’s not without risk. A new research paper published by the American Heart Association suggests that, for adults with insomnia, the sleep aid could be linked to poorer heart health.

Researchers looked at five years of medical records from 130,828 people diagnosed with insomnia and found that those who were prescribed and took melatonin for 12 months or more had about a 90% higher chance of heart failure over five years compared to those who didn’t.

Extended use of the sleep aid was also linked to hospitalization for heart failure and to death from any cause among people with chronic insomnia, according to the research presented at the American Heart Association’s Scientific Sessions 2025.

Heart failure occurs when the heart can’t pump effectively enough to meet the body’s needs. It can often be managed with medication and lifestyle changes, but it can also cause abnormal heart rhythms, liver damage, and, in severe cases, death.

The researchers stressed that findings do not prove melatonin causes heart problems, but do raise new questions about how safe it is to take the sleep supplement for extended periods.

“Melatonin supplements may not be as harmless as commonly assumed. If our study is confirmed, this could affect how doctors counsel patients about sleep aids,” Dr. Ekenedilichukwu Nnadi, a lead author of the study and chief resident in internal medicine at SUNY Downstate/Kings County Primary Care in Brooklyn, New York, said in a press release.

It’s important not to extrapolate these findings to people without chronic insomnia, since that population wasn’t studied. The study focused specifically on people with chronic insomnia who regularly use melatonin — not those who occasionally take the supplement to help with insomnia or jet lag.

“For me, one of the biggest questions is the chicken-and-egg problem: is melatonin contributing to cardiovascular risk, or is chronic melatonin use identifying a group of patients who already have more complicated sleep or medical problems?” said Dr. Salma Patel, a physician in internal medicine and sleep medicine and associate dean and professor at the University of Arizona, who is not affiliated with the study.

The need to regularly rely on sleep aids could also be a sign that an underlying health problem contributing to insomnia isn’t being addressed, Nnadi told NBC News.

In the press release, he added that people with more severe insomnia, depression, anxiety or other conditions may be more likely to use melatonin and could independently have a different cardiovascular risk.

“Worse insomnia, depression/anxiety, or the use of other sleep-enhancing medicines might be linked to both melatonin use and heart risk,” Nnadi said.

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

And an underlying sleep problem may not be insomnia at all, Patel said. Other disorders can cause sleep disturbances and could potentially be associated with cardiovascular risk, too.

“Sleep disturbance can occur with obstructive sleep apnea and other sleep-related breathing disorders, circadian rhythm sleep-wake disorders, restless legs syndrome and other sleep-related movement disorders, parasomnias, psychiatric conditions, medications, and underlying medical illness,” he said. “These conditions can also coexist with insomnia.”

That distinction is especially important when the outcome being studied is cardiovascular disease.

“Some of these underlying conditions, particularly sleep-disordered breathing, have cardiovascular implications themselves,” Patel said. “Patients with greater medical complexity or more persistent sleep symptoms may also be more likely to use a sleep aid chronically.”

In any case, if someone finds that they need melatonin night after night for months or years, Patel said, it may be worth looking into why that is.

“Persistent difficulty sleeping deserves an appropriate evaluation rather than simply treating the symptom indefinitely,” he said. “The problem may be chronic insomnia disorder, but it could also be another sleep disorder, a circadian issue, a medical or psychiatric condition, a medication effect, or another contributor to disrupted sleep.”

For people with chronic insomnia disorder, cognitive behavioral therapy for insomnia, or CBT-I, remains the gold-standard treatment, Patel said. Rather than simply treating sleeplessness, CBT-I addresses the thoughts and behaviors that can contribute to sleep problems and helps people develop healthier sleep habits.

In other words, if you’re reaching for melatonin every evening just to get through the night, it may be worth looking beyond the supplement to figure out what’s keeping you awake.

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