Preliminary research suggests that long-term use of melatonin, a popular sleep supplement, is associated with a significantly higher risk of heart failure, hospitalization for heart failure, and death from any cause in individuals with chronic insomnia.
The findings, presented at the American Heart Association's Scientific Sessions 2025, do not definitively prove that melatonin causes these increased risks. However, they are prompting new questions about the safety of a supplement often perceived as a natural and harmless sleep aid.
Melatonin, a hormone naturally produced by the brain, regulates the body's sleep-wake cycle. Synthetic versions are widely used for insomnia and jet lag and are available over-the-counter in many places, though regulation and product consistency can vary significantly.
In the study, researchers analyzed electronic medical records of adults with chronic insomnia. Those with at least one year of recorded melatonin use were compared to similar individuals with no documented melatonin use. The study excluded individuals already diagnosed with heart failure or taking other sleep medications.
The analysis revealed that individuals using melatonin long-term had approximately a 90% higher chance of developing heart failure over a five-year period compared to non-users. Furthermore, the melatonin group was nearly 3.5 times more likely to be hospitalized for heart failure, and they also experienced a nearly doubled risk of death from any cause.
"Melatonin supplements may not be as harmless as commonly assumed," stated lead author Dr. Ekenedilichukwu Nnadi. "If our study is confirmed, this could affect how doctors counsel patients about sleep aids."
Despite the concerning associations, the study has notable limitations. Melatonin's availability (prescription vs. over-the-counter) varies globally, and researchers could not determine participants' locations. Also, the reliance on electronic medical records means that over-the-counter use not recorded could have misclassified participants. Information on the severity of insomnia or other co-occurring psychiatric conditions was also missing, factors that could influence both melatonin use and cardiovascular risk.
