Taking melatonin to fall asleep might come with an unexpected side effect, according to new research from the American Heart Association.
A review of health records from more than 130,000 adults found that people who used melatonin for a year or longer were significantly more likely to develop heart failure, be hospitalized for it, or die from any cause within five years.
The findings were presented on Monday at the association’s Scientific Sessions 2025 in New Orleans.
“Melatonin supplements may not be as harmless as commonly assumed,” Dr. Ekenedilichukwu Nnadi, the study’s lead author, said in a statement. “If our study is confirmed, this could affect how doctors counsel patients about sleep aids.”
Here’s the original press release for anyone interested: https://newsroom.heart.org/news/long-term-use-of-melatonin-supplements-to-support-sleep-may-have-negative-health-effects
The most important sentence: “They were matched with peers in the database who also had insomnia but never had melatonin recorded in their health records. People were excluded from the analysis if they had previously been diagnosed with heart failure or had been prescribed other sleep medications.” There are a few other sentences describing how well the control group was matched. I think it was a well-designed study.
I think there is still a risk of bias present, though, because people who decide to take melatonin might have more severe insomnia compared to people who just decide to just “live with it” and are not using sleep aids.
The next step should be a randomized clinical trial looking at heart failure rate in patients with insomnia dosed with melatonin versus placebo and/or a different medication. Until then, correlation does not mean causation. I don’t think such a study will be done in the US because melatonin is considered a dietary supplement and is not subject to the same degree of regulation as medicine. Maybe in the UK, since melatonin is prescription only?