Brazil study warns nightly melatonin carries surprising risk

A new study presented at the American Heart Association’s 2025 Scientific Sessions suggests that long-term use of melatonin in people with insomnia may be linked to a higher risk of heart failure. The findings challenge the common belief that melatonin is a safe and natural sleep aid.

Researchers reviewed five years of health records for more than 130,000 adults with diagnosed insomnia. They compared those who had taken melatonin for at least one year with those who did not take the supplement. The goal was to assess the risk of cardiovascular disease.

The results showed that about 4.6% of long-term melatonin users developed heart failure, compared with 2.7% of non-users. That represents a nearly 90% higher risk. In addition, 19% of melatonin users were hospitalized for heart failure during the study period, versus 6.6% of non-users. The death rate from any cause was also higher among melatonin users: 7.8% compared with 4.3%.

Dr. Ekenedilichukwu Nnadi, the lead author of the study, said in a statement that the findings were striking. “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 other risk factors.”

The researchers emphasized that the study shows an association, not proof that melatonin causes heart failure. Still, they noted the consistency of the data warrants caution.

There are important nuances in the findings. Chronic insomnia itself is independently linked to a higher risk of heart problems. People who rely on melatonin for more than a year may have more severe sleep disruptions, and melatonin use could be a marker of poor sleep health rather than a direct cause of heart failure. The study identified melatonin users based on prescription records, which is common in many countries where the supplement requires a prescription. In the United States, melatonin is available over the counter, so many users may have been incorrectly grouped as non-users. This misclassification makes it harder to determine the exact size of the difference between the groups.

Experts have long warned about the unknown safety effects of melatonin. This study adds more reason to be cautious. While short-term, appropriately dosed melatonin may help with occasional jet lag, it is not intended for nightly long-term use.

For people who have trouble sleeping, there are alternatives. Improving sleep hygiene is a good first step. This includes avoiding alcohol late at night, keeping the bedroom dark and cool, and reducing screen time before bed. For those who want a supplement, magnesium is an option. Magnesium is an essential mineral that many people do not get enough of through diet alone. Low magnesium levels can contribute to stress, muscle tightness, and restless sleep. Taking magnesium before bed can help calm the body and mind by activating receptors for GABA, a neurotransmitter that quiets an overactive nervous system. This can help with falling asleep and staying asleep.

Many sleep supplements are available, and some are magnesium-based. The study’s takeaway is that while the research is preliminary, it suggests that long-term nightly melatonin use may carry more risks than previously thought. Short-term use, good sleep habits, and nutrients like magnesium remain safer ways to improve sleep naturally.