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Melatonin
Executive summary
New, large observational analyses presented at American Heart Association meetings in 2025 report that people with chronic insomnia who used melatonin for at least a year had higher rates of heart failure, heart‑failure hospitalizations and all‑cause death compared with matched nonusers — for example, one U.K. cohort showed about 4.6% vs. 2.7% heart‑failure incidence over five years (roughly a near‑doubling) [1] [2]. These findings are preliminary, come from abstracts or conference presentations and cannot prove causation; major outlets and professional groups urge caution and more research rather than immediate alarm [3] [4] [1].
1. What the new studies actually found — surprising associations, not proof of harm
Researchers analyzing large electronic‑health‑record cohorts reported that long‑term melatonin use (commonly defined as at least one year of regular use for insomnia) was associated with higher hazards of heart failure, increased heart‑failure hospitalizations and roughly doubled all‑cause mortality in some analyses [5] [6]. One presented U.K. analysis compared 65,414 adults with insomnia who took melatonin for ≥1 year to matched controls and found almost 5% experienced heart failure versus almost 3% in nonusers [1]. Press summaries and medical outlets emphasize these are associations from observational data and cannot establish cause and effect [3] [2].
2. Why experts urge caution — limits of the evidence
Medical commentators and the news releases stress several limitations: the reports are conference abstracts or preliminary presentations (not yet peer‑reviewed full manuscripts), observational designs cannot eliminate residual confounding (for example, worse insomnia, comorbid depression or other treatments could link both to melatonin use and heart risk), and results contradict prior, smaller or different studies that did not show harms [3] [4] [1]. The American Heart Association’s communication explicitly notes that these abstracts are preliminary until published in peer‑reviewed journals [3].
3. How big is the risk in real terms — rates vs. relative increases
Coverage translates the statistical signals into absolute numbers to show context: in one analysis the absolute heart‑failure rates were relatively low — ~4.6% with melatonin vs. ~2.7% without over five years — which yields a large relative increase but a modest absolute difference for individuals in that sample [2]. ScienceDaily and other summaries highlighted larger relative multipliers (e.g., near‑doubling of mortality or 3.5× hospitalizations in some framing), but those figures come from specific subgroup analyses and need peer review [6] [5].
4. What we already know about melatonin safety from established guidance
Before these conference findings, major clinical sources described melatonin as generally safe for short‑term use with common, mostly mild side effects like drowsiness, headaches, dizziness and vivid dreams; serious adverse reactions were described as rare [7] [8] [9]. Dosage guidance emphasizes that small doses often suffice and that higher doses increase side effects; long‑term safety data have been limited historically [10] [9] [11].
5. Competing interpretations and potential hidden agendas
Some outlets and researchers frame melatonin as a newly revealed cardiovascular hazard, while others — including sleep specialists quoted in reporting — argue the association may reflect confounding by indication (people with worse insomnia or other health issues both take melatonin and have higher baseline cardiac risk) and therefore does not prove melatonin causes heart disease [4] [2]. Note also that melatonin is widely marketed and sold as a dietary supplement in some countries, which creates commercial incentives to emphasize safety; conversely, cardiovascular societies may err on the side of caution when preliminary signals arise [3] [5].
6. Practical takeaways for readers and patients
If melatonin helps your sleep, experts in reporting have counseled not to abandon it abruptly but to discuss ongoing use with your clinician, especially if you have cardiovascular risk factors or chronic insomnia; monitor for new evidence as full studies undergo peer review [1] [4]. For new or persistent insomnia, evidence‑based nonpharmacologic treatments (e.g., cognitive‑behavioral therapy for insomnia) are available and recommended by sleep experts when appropriate (available sources do not mention specific CBT guidance in these snippets).
7. What to watch next — what would strengthen or refute these signals
Look for peer‑reviewed publications of the conference abstracts, stratified analyses that better adjust for baseline illness severity, randomized trials of longer‑term melatonin vs. placebo (which would be decisive for causality), and independent cohort replications in populations beyond the U.K. or the electronic‑record datasets used in the initial reports [3] [5]. Until then, major outlets recommend balanced caution: the association raises safety questions but does not prove melatonin is the cause [3] [4] [2].
Limitations: this summary relies on preliminary conference and news reporting; full peer‑reviewed data and mechanistic studies are not yet available in the cited sources [3] [6].