Myth or fact

Does melatonin cause heart failure?

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By GyroscopeUpdated November 14, 20267 sources

That hasn’t been shown. The headline came from a 2025 conference abstract that hadn’t been peer reviewed, which found more heart failure in people with insomnia who had melatonin in their health records for a year or more. It couldn’t separate melatonin from how bad their insomnia was, and over-the-counter users were counted as non-users. A 2026 analysis of US national survey data found no link.

Checked 2026-11-14. No peer-reviewed paper from the abstract’s authors had been published.

Why it sounded convincing

It had a huge number of people, a respected name and a big percentage. In November 2025 the American Heart Association put out a news release ahead of its Scientific Sessions. It said long-term melatonin users with insomnia had about a 90 percent higher chance of heart failure over five years. A lot of people with a jar on the nightstand wondered whether to stop.

Umbrellas and rain

It’s like noticing that people who carry umbrellas get wet more often. The umbrellas aren’t making it rain. People carry them because it’s raining.

People who take a sleep aid every night for over a year often have worse insomnia, and more of the things that come with it, than people who don’t. If those things also raise heart risk, melatonin will look guilty whether it did anything or not.

What the abstract found

The researchers used a large international database of health records. They took 130,828 adults diagnosed with insomnia, average age 55.7, 61.4 percent women. People with melatonin recorded in their records for 12 months or more went in the melatonin group. People with no melatonin anywhere in their records went in the comparison group, matched on other risk factors. Anyone with earlier heart failure or other sleep medicines was left out.

Over five years:

The result was similar when they looked only at people with at least two melatonin prescriptions filled at least 90 days apart.

What it couldn’t tell

The release listed the limits itself:

• It wasn’t peer reviewed. Abstracts at the meeting aren’t, and the findings count as preliminary until a full paper is published.
• Over-the-counter users were in the wrong group. Melatonin needs a prescription in some countries in the database, like the UK, and not in others, like the US. Anyone buying it off the shelf had no record of it, so they were counted as non-users.
• There was no measure of how bad the insomnia was, and no data on depression, anxiety or other psychiatric conditions. The lead author said worse insomnia, depression or anxiety, or other sleep medicines might be linked to both melatonin use and heart risk.
• It can’t show cause and effect, as the authors said.

Marie-Pierre St-Onge of Columbia University, who chaired the American Heart Association’s 2025 statement on sleep health and wasn’t part of the study, said in the same release that she was surprised doctors would prescribe it for more than a year, and that people shouldn’t take it long term without a proper reason.

What came next

In 2026 two researchers went back to the US National Health and Nutrition Examination Survey, a nationally representative survey of US adults from 1999 to 2018. Melatonin users differed a lot from non-users from the start, mostly in sleep trouble and depression. After adjusting for those differences, recent melatonin use wasn’t significantly linked to heart disease or heart failure. The authors added that their data don’t prove melatonin is safe for the heart either.

Another 2026 paper described the heart failure finding as coming from a single unpublished conference abstract that hadn’t been peer reviewed or independently checked. Its authors proposed a possible route through the hormone prolactin, and called it speculative and unconfirmed.

The best case for worrying

“130,828 people is a lot, and every outcome pointed the same way. Long-term trials don’t exist, so nobody can say it’s safe.” That last part is true. A 2019 review of 37 trials said the lack of long-term trials limits what anyone can conclude about continuous use, and the US National Center for Complementary and Integrative Health says long-term safety information is lacking.

But a big sample doesn’t fix a lopsided comparison. It makes the wrong answer look more certain. Settling it would take a study that knows who really takes melatonin, including from the store, and how bad their sleep was to begin with.

There is one heart-related effect with a trial behind it. In 47 people whose blood pressure was well controlled on nifedipine, 5 mg of melatonin at night for 4 weeks raised systolic pressure (the top number) by 6.5 points. If you take blood pressure medicine, that’s a reason to ask first. Side effects, medicines, pregnancy, children and the heart study has the rest.