Potential Health Risks Linked to Prolonged Melatonin Supplement Use for Sleep

In an eye-opening preliminary investigation set to be unveiled at the American Heart Association’s Scientific Sessions 2025, researchers have identified a potentially wrenching association between the widespread, long-term use of melatonin supplements and significant cardiovascular risks—including heart failure and mortality—among adults grappling with chronic insomnia. This study leverages an expansive database encompassing the medical records of more than 130,000 individuals, making it one of the foremost examinations into the systemic consequences of melatonin, a hormone largely heralded for its sleep-regulating qualities but until now, scarcely scrutinized from a cardiovascular perspective.

Melatonin, chemically identical to the hormone naturally produced by the pineal gland, is instrumental in orchestrating the circadian rhythm that governs human sleep-wake cycles. Endogenously, melatonin secretion surges in darkness and wanes with daylight, facilitating restful sleep. Its synthetic analogs have flooded the over-the-counter supplement market globally, lauded for their purported safety profile and efficacy in countering insomnia and circadian misalignments such as jet lag. However, this newly released epidemiological data prompts a critical reevaluation of melatonin’s long-term safety, particularly where cardiovascular health is concerned.

The study adopts a robust methodological framework by categorizing chronic insomnia patients into two cohorts: those with documented melatonin intake for a minimum of one year—the “melatonin group”—and a matched “non-melatonin group” with no recorded exposure to the compound. Through meticulous propensity score matching on 40 variables—including demographics, comorbidities, medication history, and vital statistics—the study minimizes confounding bias, striving for an apples-to-apples comparison to articulate more accurate risk estimations.

Over a five-year follow-up period, the melatonin cohort exhibited an approximately 90% elevated incidence of new heart failure diagnoses compared to their non-melatonin counterparts (4.6% vs. 2.7%). This startling figure was mirrored in a sensitivity analysis with participants who filled two or more melatonin prescriptions spaced at least 90 days apart, wherein an 82% increased risk was observed. These results underscore a consistent signal linking prolonged melatonin usage with a meaningful increase in heart failure risk among people with insomnia.

Beyond diagnosis, the severity of outcomes was further elucidated, revealing that individuals taking melatonin were nearly 3.5 times as likely to experience hospitalizations related to heart failure. The analysis also indicated a doubling in the all-cause mortality rate within this group (7.8% versus 4.3% over five years), raising profound questions about melatonin’s systemic impact beyond its immediate sleep-promoting effects.

These findings stand in stark contrast to the common perception of melatonin as an innocuous supplement, challenging both clinicians and consumers to weigh potential cardiovascular hazards. Dr. Ekenedilichukwu Nnadi, the study’s lead author, underscored the urgency of this paradigm shift, emphasizing that melatonin’s safety—long taken for granted—may require reconsideration in clinical guidance and public health messaging.

It is key to recognize, however, that this study’s retrospective nature precludes definitive causal inferences; the relationship observed remains associative rather than demonstrative of causation. Moreover, the study contends with inherent limitations, such as the mixture of healthcare systems from countries where melatonin requires prescriptions (e.g., the UK) juxtaposed with regions where it is widely accessible over the counter (e.g., the U.S.). The de-identified dataset precluded precise geographic localization of patients, potentially conflating melatonin exposure classification.

Additional confounders, including insomnia severity, psychiatric comorbidities like anxiety or depression, and use of adjunctive sleep therapeutics, were not fully accounted for due to data constraints. Consequently, the elevated cardiovascular risks might reflect more complex interactions between these variables and melatonin consumption rather than direct pharmacological causation.

Marie-Pierre St-Onge, Ph.D., C.C.S.H., FAHA, a leading expert unaffiliated with this work, highlighted the clinical implications, urging both physicians and patients to reconsider chronic melatonin use. She pointed out that, especially in the U.S., melatonin is not formally approved to treat insomnia, and prolonged self-medication without appropriate medical oversight could yield unforeseen health detriments, aligning with this study’s cautionary findings.

The biological mechanisms potentially underpinning the association between long-term melatonin supplementation and heart failure risk remain speculative but warrant urgent exploration. Melatonin exerts pleiotropic effects on cardiovascular physiology, including modulation of blood pressure, antioxidative functions, and inflammatory pathways. Whether sustained exogenous melatonin dysregulates endogenous rhythms or cardiac cellular homeostasis, leading to maladaptive remodeling and compromised myocardial function, is an open field for translational research.

This seminal work harnesses the globally accessible TriNetX research network, compiling real-world evidence from thousands of institutions and enabling unprecedented scale in epidemiological analyses. With over 65,000 melatonin-exposed individuals analyzed, the statistical power lends weight to these preliminary findings, although the scientific community awaits peer-reviewed, full manuscript publication for granular data validation.

In summary, while melatonin remains a cornerstone in managing sleep disturbances, this study articulates a crucial need for judicious prescribing practices and public awareness surrounding its extended use. Until further prospective, mechanistic studies illuminate the intricacies of melatonin’s impact on cardiac function, healthcare providers should weigh risks, monitor patients closely, and perhaps prioritize alternative insomnia therapies with more established safety profiles.

Ultimately, this provocative research piece serves as a clarion call to recalibrate clinical and consumer perceptions of sleep supplements. As melatonin’s popularity escalates, so too must our vigilance and scientific rigor in deciphering its nuanced, long-term effects on the human cardiovascular system—turning the spotlight on an underestimated public health concern with potentially wide-reaching consequences.