People who took melatonin for at least a year were three times more likely to be hospitalized for heart failure. But the correlation between the two things is not as linear as it seems.
A study presented at the American Heart Association scientific meetings has raised concerns about melatonin, one of the most prescribed sleep aids in the UK.
The findings suggest that long-term users face an increased risk of heart failure. However, preliminary data requires careful analysis before sounding the alarm.
Melatonin has been prescribed in the UK for almost two decades, with 2.5 million prescriptions issued in England alone last year. The medicine is a synthetic version of the hormone naturally produced by the brain — the so-called “hormone of darkness”, responsible for regulating our sleep and wake cycle.
For years, it has been considered safe for treating short-term sleep problems in adults and, under expert supervision, in children with cognitive disabilities or ADHD.
The study, published only as a brief summary, analyzed electronic health records of about 130,000 adults with sleep difficulties over five years – half of whom were taking melatonin and the other half of whom were not.
People who took melatonin for at least a year were three times more likely to be hospitalized for heart failure than those who did not take it (19% of users versus 6.6% of non-users). Long-term users also had higher rates of heart failure diagnosis and all-cause mortality.
The researchers attempted to balance the comparison by matching users and nonusers on 40 different factors, including age, health conditions and medication. Even so, the study revealed only an association, not a cause-and-effect relationship — and this distinction is crucial. The correlation does not prove that melatonin caused heart failure.
The devil is in the details
As always, the missing details are decisive. So far, there is only a 300-word summary of the study, which means that essential information – such as melatonin dosage, insomnia severity and lifestyle factors – has not been disclosed.
The study methodology raises some doubts. It relied on electronic medical records rather than direct patient tracking or interviews, which can leave gaps in the data. The investigation used the TriNetX Global Research Network, a vast international database. However, medical practices and clinical records vary significantly between hospitals and countries, which can skew results.
Not UK, Melatonin is a prescription medicine for specific conditions. In the United States, it is sold without a prescription, and these purchases are rarely recorded in medical records. This means that some people classified as “non-users” may actually be taking melatonin, which complicates the comparison.
The missing piece of the puzzle
Even assuming that both groups were correctly identified and paired, an essential question remains: why one group received melatonin and the other did not.
Perhaps the people prescribed it suffered from more severe or disruptive sleep problems – symptoms that may reflect underlying health problems, including heart disease. In that case, melatonin may just be a marker of existing risk, not the cause of it.
Interestingly, previous studies in heart failure patients have suggested that melatonin may even protect heart health by improving psychological well-being and heart function. Other research has indicated that it may alleviate symptoms in people with heart failure and serve as a safe complementary therapy.
As the study only exists in abstract form it has not yet been peer-reviewed, and information about the methods and results remains limited. While the findings are relevant and raise legitimate questions about the long-term risks of using this supplement, are far from conclusive. More studies are needed to determine whether long-term melatonin use affects heart health — and if so, how.
The clinical balance
Bad sleep doesn’t just affect the heart; It is also associated with metabolic, mental health and immune system problems, among others.
Typically, doctors start with lifestyle changes, improving sleep habits, and cognitive behavioral therapy. But when these measures do not work, the short-term medication may be necessary to restore healthy sleep patterns and prevent additional complications.
The melatonin story isn’t over yet — it’s just beginning.
Until more complete evidence emerges, panicking would be premature.
