Long-term use of melatonin, a widely used sleep supplement, was linked to a higher risk of heart failure, hospitalization for heart failure, and death from any cause among people with chronic insomnia, according to preliminary research presented at the American Heart Association's Scientific Sessions 2025. The findings do not prove that melatonin itself caused the increased risks. However, they raise new questions about the long-term safety of a supplement that many people view as a harmless or "natural" way to improve sleep.
Melatonin is a hormone made naturally by the pineal gland in the brain. It helps control the body's sleep and wake cycle, also known as the circadian rhythm. Levels of the hormone typically rise when it gets dark and fall during daylight.
Synthetic melatonin is chemically identical to the hormone produced by the body. It is commonly used for insomnia (difficulty falling and/or staying asleep) and jet lag. Melatonin supplements are available over the counter in many countries, including the U.S.
In the U.S., over-the-counter supplements are not regulated, so each brand of supplement can vary in strength, purity, etc. For the new study, researchers divided participants according to their documented melatonin use. People with at least one year of melatonin use recorded in their electronic medical records were placed in the "melatonin group." Those with no record of melatonin use anywhere in their medical records were assigned to the "non-melatonin group." "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," said Ekenedilichukwu Nnadi, M.D., lead author of the study and chief resident in internal medicine at SUNY Downstate/Kings County Primary Care in Brooklyn, New York. Researchers Looked for Long-Term Heart Risks Melatonin is often promoted as a safe sleep aid, but researchers say there is limited evidence about its cardiovascular safety when taken for extended periods. That uncertainty led the team to investigate whether long-term melatonin use might be associated with heart failure among people who already had chronic insomnia.
Heart failure does not mean that the heart has completely stopped working. It develops when the heart cannot pump enough oxygen-rich blood to meet the body's needs. According to the American Heart Association's 2025 Heart Disease and Stroke Statistics, the condition affects about 6.7 million adults in the U.S.
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