Recent media headlines have sparked concern about the safety of melatonin, one of the most commonly used sleep supplements worldwide, after reports suggested a possible link with heart failure. The claims stem from an unpublished observational study conducted in the United States, which is scheduled to be presented at an upcoming scientific meeting of the American Heart Association (AHA) in New Orleans.
Sleep and cardiovascular specialists, however, have cautioned that the findings should not be interpreted as evidence that melatonin causes heart disease. They emphasise that the research has not yet undergone peer review and identifies only an association, not a causal relationship.
What Did the Study Examine?
The study analysed international medical records from more than 130,000 adults diagnosed with insomnia. Participants were divided into two groups: those who had taken melatonin supplements for at least one year and those with no documented history of melatonin use.
Led by Dr Ekenedilichukwu Nnadi of SUNY Downstate Health Sciences University in Brooklyn, United States, the research team followed participants for five years to assess the incidence of heart failure, a condition in which the heart is unable to pump sufficient blood to meet the body’s needs.
According to the analysis, the incidence of heart failure was 4.6% among melatonin users, compared with 2.7% in non-users. Statistically, this translated into a reported 90% higher relative risk among those who had used melatonin. The study also observed higher rates of hospitalisation for heart failure and increased overall mortality within this group.
Association Does Not Mean Causation
Dr Nnadi acknowledged that while the results are attention-grabbing, they should not be overstated. He stressed that the study demonstrated correlation rather than causality, a distinction that can easily be lost in public reporting.
Independent experts echoed this view. Dr Sujay Kansagra, a sleep medicine specialist at Duke Health in the United States, suggested that insomnia itself, or underlying conditions linked to poor sleep — such as undiagnosed obstructive sleep apnoea — could plausibly explain the increased cardiovascular risk. In this scenario, melatonin would be an “innocent bystander” rather than the cause.
Key Limitations of the Research
Several methodological weaknesses limit the conclusions that can be drawn. One major issue is that the study only captured prescribed melatonin use. In the United Kingdom and several European Union countries, melatonin is available only by prescription, whereas in the United States and other regions it is widely sold over the counter. As a result, some participants categorised as non-users may, in fact, have been taking melatonin without it being recorded in their medical files.
Additionally, the study lacked data on dosage, duration beyond one year and severity of insomnia, all of which could influence cardiovascular outcomes. Experts also noted that, despite the reported increase, the absolute risk of heart failure remained relatively low in both groups.
To establish whether melatonin directly affects heart health, researchers would need randomised controlled trials comparing melatonin with placebo — a standard that observational studies cannot meet.
What Do These Findings Mean for the Public?
Given the study’s limitations, specialists agree that the evidence is currently insufficient to conclude that melatonin increases the risk of heart failure or causes cardiovascular harm. Nonetheless, the findings highlight how little is known about the long-term safety of many dietary supplements.
Although melatonin mimics a hormone naturally produced by the body, experts warn that this does not automatically make supplemental use risk-free. Research has shown that melatonin can be helpful for jet lag and circadian rhythm disturbances, but most sleep specialists agree it is not an effective long-term treatment for chronic insomnia. In many trials, its benefits are modest and often comparable to placebo.
Evidence-Based Approaches to Insomnia
Sleep experts consistently emphasise that sustainable improvements in sleep usually require behavioural interventions rather than quick fixes. Cognitive behavioural therapy for insomnia (CBT-I), maintaining regular sleep schedules and avoiding stimulants such as caffeine and alcohol before bedtime remain the most effective, evidence-based strategies.
As researchers prepare to submit the study for peer-reviewed publication in 2026, clinicians and patients alike are encouraged to interpret early findings with caution. For now, the research serves less as a warning against melatonin itself and more as a reminder of the need for rigorous evaluation of widely used supplements and greater public understanding of their limitations.