Long‑term melatonin linked to heart failure and higher mortality? New US data raise red flags — what to do next

Melatonin and heart risk: what the new US data mean for regular users

Melatonin is sold everywhere as a gentle, “natural” sleep aid — an over‑the‑counter shortcut to a better night. Its image is so reassuring that many of us reach for it casually, night after night. But a large observational study presented at the American Heart Association Scientific Sessions 2025 raises questions: among adults with chronic insomnia, long‑term melatonin use was associated with higher rates of heart failure, hospital admissions and overall mortality. These preliminary findings don’t prove causation, but they invite a serious rethink of how we use melatonin — especially for chronic, nightly consumption.

What the study looked at

Researchers analysed electronic health records for over 130,000 adults diagnosed with chronic insomnia. They compared patients who had used melatonin for at least one year with those who had never used it. Importantly, study participants did not have a prior diagnosis of heart failure and were not taking other prescription sleep medications — a design intended to isolate melatonin’s potential effects.

Key findings in plain terms

Nearly doubled risk of developing heart failure in long‑term melatonin users compared with non‑users.

More than three times the risk of hospitalisation for heart failure among chronic users.

Almost twofold increase in all‑cause mortality during the observation period.

These are striking associations, but they come with the caveat that observational data can be influenced by confounding factors. Still, the magnitude of the effect — especially for heart failure admissions — is large enough to merit attention from clinicians, regulators and consumers.

Possible explanations and unanswered questions

Several mechanisms could hypothetically link melatonin and cardiovascular risk, though none are proven in humans at population scale.

Direct physiological effects: melatonin influences circadian rhythms and nocturnal blood pressure regulation; in susceptible people, altering these cycles chronically might stress the heart.

Reverse causality or confounding: people with emerging but undiagnosed cardiovascular disease may have worse sleep and therefore be more likely to take melatonin, making the drug appear associated with outcomes that were already on course.

Dose and formulation: over‑the‑counter melatonin varies in dose and purity; sustained, high dosing could be different from short, low‑dose use.

The authors tried to reduce confounding — for example by excluding people with prior heart failure and examining those with repeat prescriptions — but only randomised trials can robustly separate cause and effect.

Who might be most at risk?

The study focused on adults with chronic insomnia, not occasional users. That suggests the warning is particularly relevant for:

People taking melatonin nightly for months or years.

Older adults and those with cardiovascular risk factors (high blood pressure, diabetes, obesity).

Anyone using higher‑dose or compounded melatonin products without clinical supervision.

Practical guidance for readers

Do not panic: this is not definitive proof that melatonin causes heart failure, but it’s an important signal that warrants caution.

Talk to your GP: if you use melatonin regularly, especially long term, discuss it with your clinician — particularly if you have risk factors for heart disease.

Review dosing and necessity: try to use the lowest effective dose for the shortest period. Short‑term prescribed use under medical advice remains reasonable in many cases.

Explore alternatives: cognitive behavioural therapy for insomnia (CBT‑i), sleep hygiene measures and lifestyle adjustments (timed light exposure, regular sleep‑wake schedule, reducing evening screens) are effective and carry no pharmacological risk.

What clinicians and policymakers should consider

Clinicians should ask about OTC melatonin use when assessing patients with sleep problems and consider cardiovascular risk profiling.

Regulators might reconsider guidance on long‑term, unsupervised melatonin availability and labeling — including clear advice on duration and the need for medical review in chronic insomnia.

Researchers should prioritise prospective studies and randomised trials to determine causality, dose‑response relationships and mechanisms.

How to approach sleep health safely

Quality sleep is central to health, but the route to better sleep need not be pharmaceutical. A sensible strategy is to combine behavioural interventions (CBT‑i), environmental changes (cool, dark bedroom; consistent schedule) and targeted, short‑term use of pharmacological aids under medical supervision when needed. For many, a GP or a sleep specialist can help tailor a safer long‑term plan.

Takeaway for the reader

While melatonin can be helpful and appropriate in certain contexts, the new observational data suggest that habitual, long‑term use of melatonin in people with chronic insomnia should no longer be seen as universally benign. If you or someone you love relies on nightly melatonin, it’s wise to seek medical advice, review risks, and explore evidence‑based non‑pharmacological options for sleep improvement.