Study suggests long-term melatonin use may impact heart health

Long-term use of melatonin supplements may be linked to an increased risk of heart failure hospitalization, the American Heart Association reported Monday.

Melatonin is commonly used to treat insomnia and promote sleep, often marketed as a safe, natural option. However, data on its long-term cardiovascular safety are limited, which prompted researchers to investigate its impact on heart health, specifically in adults with chronic insomnia.

The study analyzed five years of health records from more than 130,000 adults with insomnia. About 65,000 had documented long-term melatonin use (defined as one year or more), while the remainder had no melatonin recorded in their records. Patients with prior heart failure or on other sleep medications were excluded.

Results showed that over five years, about 90 percent of adults who experience insomnia, whose records indicated long-term melatonin use, had a higher chance of heart failure, compared with nonusers. Researchers accounted for multiple risk factors and health conditions but still observed a significant association between long-term melatonin use and serious cardiovascular outcomes.

“Melatonin is generally viewed as a very safe supplement…so we honestly didn’t expect to see a clear signal linking long-term use with higher rates of heart failure, hospitalizations and death,” said lead researcher Ekenedilichukwu Nnadi.

The study has not yet been peer-reviewed, and experts urge the public to avoid alarm.

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

The study has several limitations. They included the fact that over-the-counter melatonin use may not be captured in medical records, meaning some nonusers may have actually been taking the supplement. Other limitations included a lack of data on insomnia severity and psychiatric conditions.

Heart failure occurs when the heart cannot pump enough blood to meet the body’s needs and affects 6.7 million adults in the U.S., according to the 2025 Heart Disease and Stroke Statistics.