Melatonin users have 90% higher chance of developing heart failure, twice as likely to die: New study

Melatonin is one of the most commonly used over-the-counter sleep supplements in the United States. Nearly six million Americans rely on it to fall asleep faster or sleep longer.

But a new study presented at the American Heart Association (AHA) Scientific Sessions 2025 warns that long-term use may carry serious risks. Adults with insomnia who took melatonin for at least a year had a much higher chance of developing heart failure, according to researchers.

Compared with similar adults who did not use melatonin, they also have a much greater chance of being hospitalized for it or dying from any cause over the next five years.

Researchers reviewed health records from more than 130,000 adults with insomnia and no history of heart failure. They compared people who used melatonin for over a year with similar adults who never used it.

The results were striking. Long-term melatonin users had about a 90% higher chance of developing heart failure over five years.

In the United Kingdom, melatonin is available only with a prescription. People who had at least two prescriptions filled 90 days apart still showed an 82% higher risk.

Long-term users were nearly 3.5 times more likely to be hospitalized for heart failure compared with nonusers. They are almost twice as likely to die from any cause during the five-year period.

“Melatonin supplements may not be as harmless as commonly assumed,” Everyday Health quoted lead author Dr Ekenedilichukwu Nnadi as saying.

“It’s a reminder that even over-the-counter supplements can have real physiological consequences,” he added.

Nnadi thinks people rely on melatonin because access to prescription sleep medications is limited,

“Because melatonin is inexpensive and available over the counter, it’s often the only option many of my patients have,” Nnadi said.

“We also know that insomnia itself is linked to higher cardiovascular risk. I started wondering whether long-term melatonin use might influence those same pathways — either in a protective or harmful way,” Nnadi added.

Contrary views on melatonin

At the same time, the research is not conclusive. Cardiologist Tamara Horwich believes the study does not prove melatonin’s direct effect on the heart.

“There are actually studies which have suggested that melatonin may have beneficial effects on the cardiovascular system, including protection against heart failure and cardiomyopathy,” Everyday Health quoted Horwich as saying.

At the same time, ̌Horwich thinks the recent study “raises an important signal that we have to consider”.