CHICAGO — The white bottle sits on nightstands across the country. An estimated 3.1 million American adults use melatonin as a sleep aid, a figure that has nearly tripled over the past decade according to federal survey data. Most take it without a prescription, without a follow-up appointment, and without any medical record tracking how long they have been using it. A new study suggests that gap in monitoring may matter more than previously understood.
Researchers analyzing data from more than 130,000 adults with chronic insomnia found that those who used melatonin for a year or longer had an 89% higher hazard of developing heart failure compared with insomnia patients who did not take the supplement. The findings, covered in its report, were drawn from an abstract submitted to the American Heart Association and published in Circulation, the AHA’s flagship cardiovascular journal.
The scale of the effect was not confined to a single outcome. Long-term melatonin users in the study were more than three times as likely to be hospitalized for heart failure during the five-year follow-up. They were also twice as likely to die of any cause. The study tracked 130,828 adults with diagnosed chronic insomnia, roughly half of whom had used melatonin for at least one year, with the other half drawn from insomnia patients who had not used the supplement.
Those numbers demand attention. But the study’s design prevents the most straightforward reading of them.
This is an observational study. It records associations, not causes. The researchers did not randomly assign people to take melatonin or not. They drew on existing records of people who had already made that choice. Whether melatonin users and non-users were otherwise comparable at the start of the study window is the core question observational research cannot definitively answer.
The more specific risk is one that cardiologists call reverse causation. Heart failure often develops gradually, with symptoms including fatigue, breathlessness, and disrupted sleep appearing years before a formal diagnosis. People experiencing early, undiagnosed cardiac disease may be more likely to reach for an over-the-counter sleep supplement to address those symptoms. Under that scenario, the association the study found would reflect the illness selecting for the supplement, not the supplement driving the illness. The researchers acknowledged this limitation in the abstract published in its abstract.
Melatonin is a hormone the brain produces naturally to regulate the sleep-wake cycle. The synthesized version has been sold in the United States as a dietary supplement for decades, a regulatory classification that places it outside the clinical testing requirements that apply to pharmaceutical drugs. The FDA does not evaluate dietary supplements for safety or effectiveness before they reach store shelves, a regulatory gap the agency has noted while stopping short of formal action on melatonin. The supplement is widely used precisely because it is perceived as gentler than prescription sedatives, which carry dependence risks.
That perceived safety has accumulated in the absence of long-term trial data. No randomized controlled trial has been conducted specifically to measure whether sustained melatonin use carries cardiovascular risk. The AHA abstract is the first signal from a dataset large enough to generate stable estimates, and those estimates are serious enough to warrant controlled investigation even if the underlying mechanism remains unknown.
Studies of chronic low-grade inflammation have increasingly linked it to cardiovascular disease and accelerated aging, a mechanism that some researchers have proposed could connect disrupted circadian biology to downstream effects on cardiac function. Whether that pathway is relevant to the outcomes observed in this study is not established by the current data.
The American Heart Association does not currently have specific guidance on melatonin use for patients with or at risk of heart disease. The organization’s journal published the findings as a conference abstract, a standard step in the scientific process that precedes full peer review and independent statistical scrutiny. The methodology underlying the findings will need that scrutiny before clinicians are in a position to change recommendations.
For the roughly 10% of American adults who experience chronic insomnia, defined as sleep difficulty persisting for three or more months, the finding introduces a practical tension. Melatonin has been widely recommended as the first step before prescription sleep aids precisely because it was thought to carry fewer risks. If that calculation needs to be reconsidered, the evidence base that would support reconsidering it does not yet fully exist.
What does exist is a signal large enough to take seriously. An 89% elevation in heart failure hazard, if confirmed by a randomized trial, would represent a significant cardiovascular burden attributable to one of the most widely used supplements in the United States. That trial has not been announced.
Until it is, millions of Americans are navigating an assumption of safety that has not been tested at the level this data now suggests it should be.
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