Plate Nº 49 · recorded November 10, 2026
Health & Medicine ResearchReported finding
Melatonin Linked to Higher Heart Failure Rates in Large Study
A study of 130,000-plus insomnia patients links long-term melatonin use to 89% higher heart failure hazard and doubled death hazard, but prescription records and odd numbers raise doubts.
By Elena Vasquez4 min read703 words
In brief
- 4.6% of melatonin users developed heart failure over five years vs 2.7% of nonusers.
- Death rates were 7.8% among users vs 4.3% among nonusers.
- Study compared 65,414 melatonin users with 65,414 matched nonusers across 40+ variables.
- Findings appear only as a conference abstract in Circulation, not a peer-reviewed paper.
- Users were identified via prescription records, though melatonin is over-the-counter in the US.
Melatonin users showed an 89% higher hazard of developing heart failure over five years, according to a large observational study presented as a conference abstract in the journal Circulation. Death hazard was roughly doubled. The findings sound alarming for a supplement millions take as a harmless sleep aid, but the study comes with limitations big enough to give any careful reader pause.
What did the researchers find?
The study drew on a large international database of electronic health records. Researchers compared 65,414 patients with recorded long-term melatonin exposure against an equal number of patients with no recorded melatonin use. All had been diagnosed with insomnia, and anyone with a prior history of heart failure was excluded.
The team then tracked three outcomes over five years: new heart failure cases, heart failure-related hospitalizations, and deaths from any cause. The numbers weren't reassuring:
- 4.6% of melatonin users developed heart failure, versus 2.7% of nonusers.
- Deaths occurred in 7.8% of users, versus 4.3% of nonusers.
- Heart failure-related hospitalizations were reported at 19% among users, versus 6.6% among nonusers — a roughly threefold difference in hazard.
Takeaway: the gaps between the two groups were substantial, not marginal.
How fair was the comparison?
To level the playing field, the researchers used a statistical method called propensity-score matching. In plain English, that means pairing each melatonin user with a nonuser of similar profile — say, a 65-year-old with diabetes and high blood pressure matched to a nonuser with much the same history.
They matched patients on more than 40 variables, including age, medical conditions, medications, and lab measurements. That's a legitimate and rigorous technique. It also can't guarantee fairness. Confounding — the influence of an unmeasured factor — can still creep in. You can match on 40 variables and still miss the one that matters.
For instance, regular melatonin users may have more severe insomnia, or conditions like sleep apnea, which itself raises cardiovascular risk. Melatonin might be doing damage, or it might simply be along for the ride.
Takeaway: matching reduces bias, but an observational study can't prove cause and effect.
Who was actually taking melatonin?
Here's possibly the study's worst weakness. In the United States, melatonin is sold over the counter, yet the researchers identified users through prescription records. As the original analysis put it: do you know anyone who has ever gotten a prescription for melatonin?
Melatonin does require a prescription in some countries, including the UK. But elsewhere, unrecorded use is rampant. How many supposedly melatonin-free patients were buying bottles at CVS or Walmart? Nobody knows. And having a prescription doesn't prove anyone actually swallowed the pills.
So the researchers couldn't reliably establish who took melatonin, how much, or how consistently. That's a serious gap when you're trying to determine whether a substance is harmful.
Takeaway: the study's core measure of exposure is shaky, and that weakens every downstream number.
Why don't the numbers add up?
One internal oddity demands attention. Among melatonin users, 4.6% developed heart failure, yet 19% reportedly had heart failure-related hospitalizations. How can four times as many people be hospitalized for a condition as developed it?
The American Heart Association offered an explanation: hospitals may use a broader range of diagnostic codes than the specific code used to identify new heart failure cases. Fair enough. But without knowing exactly which codes were counted, the hospitalization figures — and the reported threefold increase in hazard — are hard to interpret.
Takeaway: the hospitalization numbers may reflect bookkeeping as much as biology.
Should the study be dismissed?
No. It has real strengths: more than 130,000 patients, five years of follow-up, sophisticated statistical adjustment, and a sensitivity analysis requiring multiple melatonin prescriptions in which the heart failure association held firm. Observational research has caught genuine drug safety problems before randomized trials could.
One caution: the findings exist only as a conference abstract, not a full peer-reviewed paper. Does the study prove melatonin causes heart failure? No. Is it concerning enough to warrant deeper investigation? Possibly. Until better data arrive, treat the headline numbers as a reason for questions, not panic.
via acsh.org (Source)
More from Elena Vasquez
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Correspondent covering money, funding and market shifts around general science news at SciBeat.
384 articles
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