AHA study finds potential connection between long-term melatonin usage and negative heart health outcomes

The American Heart Association (AHA) announced the results of a preliminary study that will be presented at the association’s Scientific Sessions 2025. The study found that long-term use of melatonin supplements were associated with a higher risk of heart failure diagnosis, heart failure hospitalization and death from any cause in chronic insominia. The study used a large international database in which the researchers reviewed five years of electronic health records for adults with chronic insomnia who had more than a year of melatonin use recorded in their health record. These records were matched peers who had insomnia but no melatonin use recorded. According to the study, those adults who took melatonin for more than a year had a 90% higher chance of incidence of heart failure over five years compared to non-users.

“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, MD, lead author of the study and chief resident in internal medicine at SUNY Downstate/Kings County Primary Care in Brooklyn, New York, in a statement.

”I’m surprised that physicians would prescribe melatonin for insomnia and have patients use it for more than 365 days, since melatonin, at least in the U.S., is not indicated for the treatment of insomnia. In the U.S., melatonin can be taken as an over-the-counter supplement and people should be aware that it should not be taken chronically without a proper indication,” added Marie-Pierre St-Onge, Ph.D., C.C.S.H., FAHA, chair of the writing group for the AHA’s 2025 scientific statement, Multidimensional Sleep Health: Definitions and Implications for Cardiometabolic Health. St.-Onge was not involved in this study.

Industry has been quick to respond to the results, noting that the population studied were individuals with chronic insomnia. “We recommend that consumers with chronic sleeplessness and other chronic diseases always consult with their physicians to properly diagnose and treat their medical conditions,” said Daniel Fabricant, PhD, president and CEO of the Natural Products Association (NPA; Washington, D.C.), in a press release. “The preliminary study examined whether melatonin use alters the risk of heart failure in chronic insomnia patients, which is not the supplement industry’s target population. Furthermore, the established literature demonstrates that short-term use of melatonin is safe. NPA agrees that consumers should not take melatonin supplements for chronic insomnia without a proper indication and in close consultation with a medical professional.”

The Council for Responsible Nutrition (CRN; Washington, D.C.) also urged caution in interpreting the results given that the research represents early, non-peer-reviewed data. Additionally, because those with chronic sleep conditions tend to have higher heart rate, blood pressure, and experience more cardiovascular events, the data cannot necessarily be extrapolated to healthy populations. AHA itself acknowledges the study’s limitations and Nnadi notes that “while the association we found raises safety concerns about the widely used supplement, our study cannot prove a direct cause-and-effect relationship. This means more research is needed to test melatonin’s safety for the heart.”