Melatonin, one of the world’s most widely used sleep supplements, may not be as harmless as commonly believed. A large preliminary study presented at the American Heart Association’s Scientific Sessions 2025 has found that people with chronic insomnia who used melatonin for a year or longer had a nearly 90% higher risk of developing heart failure over the following five years, compared to matched non-users.
The study analysed five years of health records for over 130,000 adults with insomnia, drawn from the TriNetX global research database. Of these, 65,414 had used melatonin for at least a year. Researchers found heart failure developed in 4.6% of long-term melatonin users versus 2.7% of non-users. The risks were even starker for secondary outcomes: melatonin users were nearly 3.5 times more likely to be hospitalised for heart failure, and death from any cause was almost twice as common in this group.
Lead author Dr. Ekenedilichukwu Nnadi of SUNY Downstate cautioned that the findings show an association, not proof of causation. Since melatonin is available over the counter and unregulated in the US, many users may not appear in medical records, potentially skewing results. The study also lacked data on insomnia severity and co-existing mental health conditions, which could independently affect heart risk.
Sleep researcher Dr. Marie-Pierre St-Onge of Columbia University, who was not involved in the study, noted that melatonin is not approved for long-term insomnia treatment in the US and should not be taken chronically without proper medical guidance.
Experts agree the findings warrant caution rather than alarm, urging further research to confirm whether melatonin itself affects cardiovascular health and why.
(Source: American Heart Association, Scientific Sessions 2025)