Melatonin & Heart Failure Risk: What the Latest Study Reveals

Widely available over-the-counter in pharmacies, melatonin is a popular sleep aid for millions. However, preliminary research presented in November 2025 at the American Heart Association (AHA) conference in Recent Orleans raises concerns about the supplement’s long-term effects. Researchers analyzed the medical records of 130,828 adults with chronic insomnia. Their analysis revealed that individuals taking melatonin for a year or longer had a higher likelihood of developing heart failure. This finding is particularly relevant for seniors, who are among the most frequent users of melatonin.

The team led by Dr. Ekenedilichukwu Nnadi, from SUNY Downstate Medical Center in Brooklyn, New York, compared two groups of insomnia sufferers over five years. One group had been taking melatonin for at least twelve months, while the other had not. Both groups were matched based on 40 criteria, including age, sex, cardiovascular history, blood pressure, and current medications.

Specifically, the observational study revealed:

It’s important to note that Here’s a statistical association, not a proven cause-and-effect relationship. The study’s results have not yet been published in a peer-reviewed scientific journal.

You may be affected without realizing it. In France, 1.4 million boxes of melatonin-based dietary supplements are sold each year, according to the Order of Pharmacists. Products containing 2 mg or less of melatonin per day are available over-the-counter without a prescription.

Seniors are the primary users. As people age, natural melatonin production declines in some individuals, leading many to turn to supplements to improve sleep. Some take them every night for months, or even years—without medical supervision. This proves this prolonged use that is associated with the risk observed in the study.

You may be affected without realizing it. In France, 1.4 million boxes of melatonin-based dietary supplements are sold each year, according to Synadiet (a figure cited by ANSES in its 2018 opinion). Products containing 2 mg or less of melatonin per day are available over-the-counter without a prescription.

Seniors are the primary users. As people age, natural melatonin production declines in some individuals, leading many to turn to supplements to improve sleep. Some take them every night for months, or even years—without medical supervision. It is this prolonged use that is associated with the risk observed in the study.

The French National Institute of Health and Medical Research (Inserm) published a detailed analysis of available studies in September 2024. The findings are nuanced. Melatonin in dietary supplements may slightly reduce sleep onset time, especially in people over 55. However, studies display little effect on nighttime awakenings or overall sleep quality.

In other words, many French individuals are taking a product with modest effectiveness for extended periods, believing it to be completely harmless. However, the ANSES already recommended in 2018 limiting use to short-term applications and avoiding prolonged self-medication.

This American study does not invalidate the occasional use of melatonin. But it underscores that a “natural” supplement is not necessarily risk-free when taken long-term, especially in people with cardiovascular risk factors.

The main takeaway from this study extends beyond melatonin itself. It concerns a widespread reflex: believing that a product sold without a prescription and marketed as “natural” carries no risk.

Researchers acknowledge several limitations to their work. Chronic insomnia itself is a cardiovascular risk factor. Depression, anxiety, or the use of other medications could likewise explain some of the results. But the signal is considered concerning enough to warrant increased caution.

One question remains unanswered: will this association be confirmed by more in-depth studies? Currently, no country has changed its regulations. But vigilance is advised—especially among those over 50 who have been taking this supplement daily for a long time.