For millions of individuals struggling with the relentless cycle of insomnia, melatonin has long served as a "natural" sanctuary. Viewed as a gentle, hormone-based supplement, it is often the first line of defense for those tossing and turning in the middle of the night. However, a jarring new study presented at the American Heart Association’s (AHA) Scientific Sessions 2025 suggests that this common bedtime ritual may carry hidden, long-term cardiovascular risks that have previously been overlooked.
According to preliminary research, the chronic use of melatonin is linked to a substantially higher risk of heart failure, hospitalization, and death. While these findings do not establish a definitive causal link, they serve as a critical wake-up call for both the medical community and the general public, suggesting that what we consider "harmless" may warrant deeper scrutiny.
The Foundation: Why Melatonin Has Become a Household Staple
To understand the weight of these findings, one must first understand the ubiquity of the hormone itself. Melatonin is a naturally occurring substance produced by the pineal gland, a pea-sized organ located deep within the brain. Its primary function is the regulation of the body’s internal clock, or circadian rhythm. Under normal conditions, melatonin levels surge as daylight fades, signaling to the body that it is time to wind down and prepare for sleep.
Synthetic melatonin, which is chemically indistinguishable from the hormone produced by the human body, has become a global phenomenon. Whether used to combat the physiological disorientation of jet lag or to manage the frustration of chronic insomnia, its popularity is fueled by the perception of safety. Unlike traditional sedatives or prescription sleep aids, which often carry risks of dependency or grogginess, melatonin is marketed and widely perceived as a benign, "natural" alternative.
In the United States, this perception is bolstered by the supplement’s status as an over-the-counter (OTC) product. Because it is not strictly regulated by the FDA in the same manner as pharmaceutical drugs, consumers are often left to navigate a landscape of varying potencies, purities, and formulations, frequently without the guidance of a physician.
Unmasking the Heart: The Research Methodology
The study, led by Ekenedilichukwu Nnadi, M.D., chief resident in internal medicine at SUNY Downstate/Kings County Primary Care, sought to fill a glaring gap in current medical literature. While melatonin is studied extensively for its sleep-inducing properties, there is a paucity of data regarding its cardiovascular safety over extended periods.
To investigate, Dr. Nnadi and his team leveraged the TriNetX Global Research Network, a massive, international repository of de-identified electronic health records. By analyzing five years of medical data, the researchers identified a cohort of adults suffering from chronic insomnia. They divided these individuals into two distinct groups: those with documented melatonin use for at least one year and a control group of individuals with no recorded use of the supplement.
To ensure the integrity of the data, the researchers implemented strict exclusion criteria. Any participant who had a pre-existing diagnosis of heart failure or who had been prescribed other sleep-enhancing medications was removed from the analysis. This ensured that the observed effects were as closely tied to melatonin usage as possible, rather than being influenced by pre-existing cardiac conditions or polypharmacy.
The Alarming Data: A Statistical Shift in Risk
The results of the analysis were, by the authors’ own admission, "striking." Among adults with chronic insomnia, those who had utilized melatonin for 12 months or longer exhibited a roughly 90% higher risk of developing heart failure over the subsequent five-year period compared to non-users. In raw numbers, the incidence of heart failure reached 4.6% in the melatonin group, compared to just 2.7% in the control group.
Seeking to validate these findings, the team conducted a secondary analysis, limiting the cohort to individuals who had filled at least two melatonin prescriptions at least 90 days apart—a proxy for consistent, long-term adherence. Even within this more specific group, the risk remained elevated at 82%.
The implications extended beyond the initial diagnosis of heart failure. The secondary analysis revealed that individuals in the melatonin group were nearly 3.5 times more likely to be hospitalized for heart failure than their counterparts. Furthermore, the mortality rate among the melatonin-using group was twice as high (7.8%) compared to the non-melatonin group (4.3%) over the five-year study period.
"Melatonin supplements are widely thought of as a safe and ‘natural’ option to support better sleep," Dr. Nnadi stated. "It was striking to see such consistent and significant increases in serious health outcomes, even after balancing for many other risk factors."
Official Perspectives: A Call for Clinical Caution
The findings have reverberated through the scientific community, prompting experts to call for a reassessment of how melatonin is recommended. Dr. Marie-Pierre St-Onge, a prominent sleep researcher and professor of nutritional medicine at Columbia University Irving Medical Center, expressed significant concern regarding the findings.
"I’m surprised that physicians would prescribe melatonin for insomnia and have patients use it for more than 365 days, since melatonin, at least in the U.S., is not indicated for the treatment of insomnia," Dr. St-Onge noted.
As the chair of the writing group for the American Heart Association’s 2025 scientific statement on multidimensional sleep health, Dr. St-Onge emphasizes that the current culture of "chronic self-medication" is fraught with danger. Her position is clear: melatonin should not be treated as a permanent solution for sleep disorders. When used without a clear medical indication or proper supervision, patients may be inadvertently exposing themselves to systemic risks that remain poorly understood.
Limitations and the Necessity of Nuance
While the statistics are compelling, the research team is the first to urge caution in interpretation. The study carries several inherent limitations that prevent it from establishing a direct cause-and-effect relationship.
1. The "Classification" Challenge
Because the study relied on electronic health records, it only captured melatonin use that was formally documented. In countries like the U.S., where melatonin is bought over the counter, many users never report their supplement habits to their primary care providers. This means that many people in the "non-melatonin" control group may have actually been regular users, potentially diluting the results or creating bias.
2. The Confounding Factor of Insomnia
The study could not account for the severity of the participants’ underlying insomnia or associated comorbidities like anxiety and depression. It is possible that individuals with more severe, treatment-resistant insomnia are more likely to seek out melatonin and are also, independently, at higher risk for cardiovascular issues. Without data on these psychological variables, it is difficult to isolate the supplement as the sole culprit.
3. Discrepancies in Data Entry
The higher rate of hospitalization for heart failure compared to new diagnoses suggests that hospital coding practices may have influenced the data. Diagnostic codes for heart failure are often triggered by secondary symptoms or related conditions, making it difficult to pinpoint exactly when the disease process began.
Looking Forward: The Future of Sleep Health
Dr. Nnadi acknowledges that the current study is only the beginning of a larger conversation. "Worse insomnia, depression/anxiety, or the use of other sleep-enhancing medicines might be linked to both melatonin use and heart risk," he admits. "Our study cannot prove a direct cause-and-effect relationship. This means more research is needed to test melatonin’s safety for the heart."
The broader implication of this research is a potential shift in the clinical management of sleep disorders. If future, more granular studies confirm these risks, it could fundamentally change how doctors counsel patients. Instead of the current "try it and see" approach, the medical community may move toward stricter, time-limited protocols for melatonin, emphasizing it as a bridge to better sleep hygiene rather than a chronic pharmaceutical crutch.
For the average consumer, the message is clear: "natural" does not necessarily equate to "risk-free." As the American Heart Association continues to prioritize the link between sleep health and cardiovascular function, patients are encouraged to have transparent conversations with their healthcare providers about their sleep habits. Before embarking on a long-term regimen of any supplement, understanding the potential impacts on the heart—our most vital organ—should be a priority for everyone.
This study, while preliminary, serves as a poignant reminder that the pursuit of a good night’s rest should not come at the expense of long-term health. The scientific community will undoubtedly be watching closely as further longitudinal data is gathered to determine whether melatonin is a silent contributor to heart disease or simply a marker for those already at risk.
