A 2025 study presented at the American Heart Association’s Scientific Sessions linked recorded long-term melatonin use with more heart-failure diagnoses among adults with insomnia. The preliminary finding prompted concern about the safety of a familiar sleep aid. [1]
In May 2026, an Open Heart paper reported a different result: its exploratory analysis of US NHANES survey data found no statistically significant association between recent melatonin use and existing cardiovascular disease or heart failure. [2]
The distinction is crucial. The first study examined recorded long-term use and later diagnoses in people with insomnia; the second examined recent use and existing disease in a general population. They do not directly contradict each other. Neither establishes that melatonin causes heart failure or that years of use are safe. The safety signal deserves investigation, and habitual use deserves review.
What the 2025 study reported
The American Heart Association publicised the findings on 3 November 2025 as preliminary conference research. Investigators examined records for 130,828 adults with insomnia, comparing documented melatonin use for at least a year with no recorded use. Over five years, heart failure diagnoses occurred in 4.6% versus 2.7%. [1]
Those proportions correspond to 46 versus 27 diagnoses per 1,000 people: an observed difference of 19, not cases proven to be caused by melatonin. [1]
Matching did not resolve missing insomnia-severity information or unrecorded over-the-counter use. These gaps leave alternative explanations unresolved. The study does not establish cause and effect. [1]
What else could explain the result?
Both groups had insomnia. That does not mean they had equally severe sleep problems or the same underlying health. Several pathways could produce the association without melatonin causing heart failure.
Greater illness burden. Chronic insomnia is more common among people with heart disease, breathing problems and chronic pain. A person whose illness disrupts sleep has more reason to seek a sleep treatment. If recorded melatonin users had more severe underlying disease, the supplement could mark that burden rather than cause the later heart failure. This is a plausible explanation, not a finding established in this cohort. [8]
More severe insomnia. A separate prospective study linked a greater number of insomnia symptoms with higher subsequent heart-failure risk. The melatonin study lacked a measure of insomnia severity. If people with worse sleep were more likely to use melatonin, that difference could contribute to the result despite both groups carrying an insomnia diagnosis. [1,9]
Disease preceding the prescription. Undiagnosed heart disease can disrupt sleep before heart failure is formally recorded. Someone could start melatonin for those symptoms and receive the diagnosis later. The medical record would put melatonin first even though the disease process came first. Researchers call this reverse causation. [2]
Differences in detection and recording. More medical contact creates more opportunities to record both supplement use and heart failure. Unrecorded over-the-counter use also blurs the comparison groups. These are potential biases; the available data do not establish their direction or size. [2]
Matching reduces measured differences. It does not eliminate unmeasured disease severity, undocumented treatment or illness that develops during follow-up. These alternatives explain why the result is not proof of harm. They do not prove that melatonin is harmless.
The newer analysis does not establish safety
In May 2026, Baryalay Khan and Bruno Bezerra Lima published an externally peer-reviewed Open Heart viewpoint containing an exploratory NHANES analysis. It included 50,929 adults, of whom 267 reported melatonin use during the previous 30 days. After adjustment, recent use was not significantly associated with existing cardiovascular disease or heart failure. [2]
This analysis does not settle the original question. It measured recent use and existing disease in a general population; the earlier study examined recorded long-term use and subsequent diagnoses among people with insomnia. Few melatonin users and wide uncertainty around the estimates further limit its conclusions. A result without statistical significance is not proof of safety. [2]
These studies answer different questions. Neither establishes the cardiovascular consequences of taking a specified melatonin product for years. [2]
The regulator’s warning deserves attention
On 19 April 2026, the Saudi Food and Drug Authority alerted professionals to a potential cardiac-failure risk. Its assessment considered the conference study and four global case reports, all lacking enough information for a proper causality assessment. The agency judged the combined evidence suggestive of a causal association, while defining safety signals as preliminary and uncertain. That warrants follow-up; it does not supply a reliable estimate of harm for an individual user. [7]
Short trials do not establish long-term safety
Randomised trials are useful because treatment assignment reduces the problem of comparing people who chose different treatments. But duration matters. A 2019 systematic review of melatonin adverse events included 37 randomised trials. Follow-up extended to 29 weeks, while most studies lasted four weeks or less. The authors found that scarce long-term trial evidence limited conclusions about continuous treatment. [3]
Tolerating a product for several nights tells us little about an uncommon outcome developing years later. Short trials cannot close that gap. Long-term safety requires evidence collected over the period people actually take the treatment.
Formulation and purpose matter
Guidelines also distinguish the reason for treatment and the formulation. The 2017 American Academy of Sleep Medicine guideline makes a weak recommendation against melatonin for adult sleep-onset or sleep-maintenance insomnia. “Weak” describes uncertainty in the recommendation; it is not a finding that melatonin causes heart failure. The guideline places medication decisions within an assessment of symptoms, other conditions, preferences and access to cognitive behavioural therapy for insomnia, or CBT-I. [4]
The 2023 European guideline makes an important distinction. It allows prolonged-release melatonin for up to three months in patients aged 55 or older, while generally recommending against fast-release melatonin for insomnia without circadian factors. CBT-I is the recommended first-line treatment. That is a defined treatment approach for a selected population. It does not endorse indefinite use of any supplement sold for sleep. [5]
Review nightly use
If melatonin has become a nightly habit, review it with a pharmacist or clinician. Bring the product, dose, timing, duration and a list of other medicines. Establish what has improved, what sleep difficulties remain and when the treatment will be reassessed. If it was prescribed, discuss changes with the prescriber.
Long-term safety remains uncertain, and interactions with other medicines require attention. The US National Center for Complementary and Integrative Health specifically advises medical supervision for people taking blood thinners or those with epilepsy. Persistent insomnia needs assessment and appropriate treatment. Increasing the supplement dose is no substitute for understanding the sleep problem. [6]
What the evidence demands next
The next studies must define the treatment precisely: who takes it, which formulation, at what dose, for which sleep problem and for how long. Reliable exposure records, meaningful sleep outcomes and cardiovascular follow-up are essential. Without them, another large dataset will leave the same questions unanswered.
The conclusion is clear: investigate the heart-failure signal and review habitual melatonin use. Claims of proven heart damage exceed the evidence. So does treating years of use as established safe. A nightly treatment deserves a clear purpose, a demonstrated benefit for the person taking it and regular reassessment.