Long-term melatonin use was associated with a roughly 90% higher risk of heart failure, 3.5 times higher hospitalization rates, and nearly double the death rate among people with chronic insomnia, according to preliminary research presented at the American Heart Association's Scientific Sessions.
The observational study analyzed five years of medical records for 130,828 adults (average age 55.7, 61.4% women) who had been diagnosed with insomnia. Of those, 65,414 had documented melatonin use for at least one year; the rest had no recorded use. Both groups were matched across 40 factors including demographics, existing conditions, and medications.
Heart failure occurred in 4.6% of the melatonin group versus 2.7% of the comparison group. When researchers tightened the criteria to people who had filled at least two prescriptions at least 90 days apart, the risk remained 82% higher. Hospitalization for heart failure was 19.0% in the melatonin group versus 6.6% among non-users, and all-cause death was 7.8% versus 4.3%.
"Melatonin supplements may not be as harmless as commonly assumed," said lead author Ekenedilichukwu Nnadi, M.D., of SUNY Downstate/Kings County. "If our study is confirmed, this could affect how doctors counsel patients about sleep aids."
The findings come with significant limitations. Melatonin is over-the-counter in the U.S. but prescription-only in the U.K., and the de-identified dataset did not include participants' locations — meaning some "non-users" may have been taking OTC melatonin without it appearing in their records. Researchers also lacked data on insomnia severity, depression, and anxiety, all of which could independently affect cardiovascular risk.
"Worse insomnia, depression/anxiety, or the use of other sleep-enhancing medicines might be linked to both melatonin use and heart risk," Nnadi acknowledged. The team emphasized the study is observational and cannot establish causation — further research is needed.
