Could the “natural” sleep aid millions swear by be quietly raising serious heart risks? New research presented at the American Heart Association’s Scientific Sessions 2025 suggests that among adults with insomnia, those taking melatonin for more than a year had a significantly increased risk of developing heart failure, being hospitalized for the problem, or dying from any cause over the next five years compared to similar adults not taking the supplement.
The record review, headed by Ekenedilichukwu Nnadi, MD, chief resident in internal medicine at Kings County Hospital and Downstate Health Sciences University, examined health records for over 130,000 adults with insomnia who never had heart failure. Long-term users-defined as those who had been on melatonin for at least 12 months-developed heart failure with an approximately 90% higher risk compared to non-users. Similarly, patients with at least two prescriptions that were filled 90 days apart saw an 82% increased risk. Rates of hospitalization due to heart failure were more striking: 19% among users versus 6.6% among non-users. The mortality risk was almost doubled: 7.8 percent versus 4.3 percent.
While the numbers are alarming, experts caution that this study cannot prove melatonin caused these outcomes. “It’s a reminder that even over-the-counter supplements can have real physiological consequences,” says Dr. Nnadi. Cardiologist Tamara Horwich, MD, says factors like socioeconomic status, mental health conditions, or the severity of insomnia may be driving both melatonin use and heart risk. She says, “There are actually studies which have suggested that melatonin may have beneficial effects on the cardiovascular system, including protection against heart failure and cardiomyopathy.”
Certainly, short-term studies have documented properties of melatonin to act as a powerful antioxidant, reducing inflammation and improving some heart-related biomarkers. In animal models, melatonin has shown the ability to regenerate pancreatic beta cells, lower blood glucose, and protect against oxidative stress. Some human studies to date have associated it with better blood pressure control and improved cholesterol profiles. But those benefits have been largely documented in controlled, short-duration trials, not in the kind of long-term, real-world use examined here.
Part of the concern lies in the unregulated nature of the supplement within the US. Because it is not a prescription drug, melatonin products are not reviewed by the FDA for strength or purity. Independent testing has identified that melatonin content can vary wildly-from -83% to +478% of the labeled dose-and some products have been contaminated with serotonin. Such inconsistencies mean consumers may be taking far more or far less than intended, with unpredictable effects on the body.
For anyone taking melatonin every night, the experts recommend talking to a healthcare professional. “Melatonin can be useful for short-term sleep issues or adjusting to jet lag, but it’s not meant to be taken indefinitely without medical guidance,” says Nnadi. And some alternatives don’t come with the same question marks. Evidence-based practices in sleep hygiene-limiting light exposure at night, keeping bedtimes consistent, and keeping the sleep environment cool and quiet-can help normalize the body’s rhythms over time.
Other non-pharmacological sleep aids, such as magnesium, L-theanine, glycine, or valerian, may also support sleep for some people, though they too should be discussed with a doctor to avoid interactions or side effects. The takeaway isn’t necessarily to banish melatonin from the nightstand but rather to use it thoughtfully and sparingly. As preventive cardiologist Nishant Shah, MD, puts it, “Now that we have this observation, this is prime time to figure out whether there’s actually a direct association of harm with sleep agents. That would be practice-changing.” Until more definitive research emerges, approaching melatonin with the same caution as any other medication-and giving lifestyle-based sleep solutions priority-may be the safest path forward.
