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Long-term melatonin use linked to 90% higher heart failure risk. A large preliminary study found that adults with chronic insomnia who used melatonin for over a year had a roughly 90% higher risk of developing heart failure over five years compared to non-users. While the findings don't prove causation, they challenge the widespread belief that melatonin is a completely safe, natural sleep aid.
Melatonin is one of the most popular sleep aids on the market — widely seen as a safe, natural option. But a large preliminary study presented at the American Heart Association's Scientific Sessions 2025 is raising some serious red flags. Researchers found that adults with chronic insomnia who used melatonin long-term had about a 90% higher risk of developing heart failure over five years compared to matched non-users.
The study drew on data from over 130,000 adults in the TriNetX Global Research Network. Participants with at least one year of documented melatonin use were compared against insomnia patients with no melatonin records. Even in a stricter sensitivity analysis — requiring at least two prescriptions filled 90+ days apart — the elevated risk held, showing an 82% higher heart failure risk.
Why it matters: This is an observational study — it cannot prove melatonin causes heart failure. But given how freely melatonin is sold over the counter in the U.S. and how many people use it chronically, these findings are a meaningful prompt for both patients and clinicians to reconsider long-term use without proper medical guidance.
