Melatonin and heart failure: how to read a preliminary study
A large study reported long-term melatonin users with insomnia had roughly 90% higher heart failure risk. That number deserves attention and a great deal of caution, here is how to hold both.
A large study reported in 2026 found that people with chronic insomnia who used melatonin long term had roughly 90% higher risk of developing heart failure over five years.
That is a big number attached to a very widely used supplement. It is also a good case study in reading this kind of finding properly, because almost every way it will be reported is misleading.
Four things to establish before reacting
It is preliminary. Presented rather than fully peer-reviewed and published. A meaningful share of preliminary findings do not survive full review, and this one has not yet been through it.
It is observational. Nobody randomized people to melatonin. Researchers looked at who took it and what happened. That design can show association; it cannot establish cause.
90% is a relative risk. It says nothing about how common the outcome is. If baseline five-year heart failure risk in a group is 1%, a 90% increase makes it 1.9%, a real increase, and not what "your risk nearly doubles" evokes. The absolute numbers are what matter for a personal decision, and relative risk is what gets printed.
The comparison group is the problem. This is the big one.
Confounding by indication
People taking melatonin long term have chronic insomnia. That is why they are taking it.
Chronic insomnia is itself an established risk factor for cardiovascular disease, including heart failure. So the study is partly comparing people with a cardiovascular risk factor to people without one, and attributing the difference to the pill they took for it.
Researchers adjust for what they can measure. Nobody adjusts perfectly, and insomnia severity is hard to capture. This pattern, a drug appearing to cause the harm its indication causes, has produced a long list of associations that did not survive better study designs.
The question "does melatonin harm hearts" and the question "do people with severe insomnia have worse cardiovascular outcomes" produce similar data and have very different answers.
What would make it convincing
- Replication in independent cohorts
- A dose-response relationship, more melatonin, more risk
- A plausible biological mechanism
- Ideally, a randomized trial, though for a cheap over-the-counter supplement one may never be funded
None of that is present yet. That does not make the finding wrong. It makes it a starting point.
What else is worth knowing about melatonin
Regardless of this study, a few things are worth knowing:
Dosing is usually far too high. Effective doses are 0.5–1 mg. Common products are 5–10 mg. More does not work better and may worsen next-day grogginess.
It is a timing cue, not a sedative. It shifts circadian phase. It is genuinely useful for jet lag and shift work, and much weaker for ordinary "cannot fall asleep" insomnia than its sales suggest.
US supplement labeling is unreliable. Analyses of melatonin products have repeatedly found actual content ranging from a small fraction of the label to several times it.
CBT-I outperforms it. Cognitive behavioral therapy for insomnia beats melatonin in trials and is the recommended first-line treatment for chronic insomnia in most guidelines.
What to do
If you take melatonin occasionally for travel, this finding is not about you.
If you take it nightly and have for years, it is worth raising with your doctor, not as an emergency, but as one input alongside whether it is still working and whether CBT-I is available to you.
And as a general habit: when a headline attaches a large percentage to a common product, look for the absolute risk, the study design, and who the comparison group was. Those three usually change the picture.
Common questions
- Is melatonin bad for your heart?
- A large preliminary study reported that people with chronic insomnia using melatonin long term had roughly 90% higher risk of developing heart failure over five years. It is observational and preliminary, so it shows an association rather than a cause, and the underlying insomnia is itself a known cardiovascular risk factor.
- What does confounding by indication mean?
- It is when the reason someone takes a treatment is itself a risk factor for the outcome being studied. People taking melatonin long term have chronic insomnia, and chronic insomnia independently raises cardiovascular risk, so the drug and the disease are hard to separate.
- Should I stop taking melatonin?
- This single preliminary finding is not sufficient reason to change treatment on your own. It is a reasonable thing to raise with your doctor, particularly if you use it nightly for years rather than occasionally for jet lag.
Sources
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