Sleep | One year on
A Year After the Melatonin Heart Study, a Regulator Has Acted and the Question Is Still Open
A study of more than 130,000 adults linked long term melatonin use to heart failure. Since then, Saudi Arabia has issued a safety signal and a second study found no link. Here is where the evidence stands.
One year ago this week, the American Heart Association put out a news release with a line that travelled fast: people with insomnia who took melatonin for a year or more were about 90% more likely to develop heart failure over the next five years.
Melatonin is sold in the US as a dietary supplement, with no prescription and no FDA approval needed, and millions of adults take it every night. So the finding landed hard. A year later, it has not been confirmed or ruled out, but it has not gone away either.
What the study found
The research, led by Dr. Ekenedilichukwu Nnadi of SUNY Downstate in Brooklyn, used electronic health records from the TriNetX network. It looked at 130,828 adults with insomnia, average age 55.7, and compared 65,414 people whose records showed at least a year of melatonin use with 65,414 matched people who had insomnia but no record of melatonin.
People who already had heart failure, or who had been prescribed other sleep medicines, were left out.
- Heart failure within five years: 4.6% of melatonin users against 2.7% of non users, a hazard ratio of 1.89.
- Hospitalisation for heart failure: 19.0% against 6.6%.
- Death from any cause: 7.8% against 4.3%, a hazard ratio of 2.09.
When the researchers tightened the definition to people with at least two melatonin prescriptions 90 days apart, the raised risk of heart failure held at about 82%.
Why it is not the final word
The study is observational. It can show that two things travel together. It cannot show that one causes the other, and the authors say so: "our study cannot prove a direct cause and effect relationship," Nnadi said.
The records had no measure of how bad each person's insomnia was, and no data on depression or anxiety. "Worse insomnia, depression or anxiety or the use of other sleep enhancing medicines might be linked to both melatonin use and heart risk," Nnadi said.
There is also a counting problem. The data found melatonin users through prescriptions. In the UK, where melatonin is prescription only, that captures users well. In the US, where it is sold over the counter, people taking it from a store shelf were counted as non users.
The work was presented as an abstract at the AHA's Scientific Sessions in New Orleans. The AHA says such abstracts are not peer reviewed and are considered preliminary. As of this week, we found no full journal paper.
What has happened since
On April 19, 2026, the Saudi Food and Drug Authority issued a safety signal titled "Safety Signal of Melatonin and the Risk of Cardiac Failure." It drew on the AHA abstract and four case reports from around the world, and rated the evidence as suggestive of a causal association while calling the signal preliminary. We found no label change or sales restriction attached to it.
In May 2026, a study in the BMJ journal Open Heart looked the other way. It used US national survey data from 1999 to 2018 covering 50,929 adults, 267 of whom had taken melatonin in the past 30 days. After adjustment, recent use was not significantly linked to heart disease or heart failure. The authors called it hypothesis generating: it was a snapshot in time, and its count of melatonin users was small.
An American Academy of Sleep Medicine spokesperson, Dr. Muhammad Rishi, told The Washington Post the original findings "warrant attention" but that the observational design limits what can be said about cause.
What it means if you take melatonin
No regulator in the US or Europe has changed its advice on melatonin because of the study. The US National Center for Complementary and Integrative Health already notes that information on the safety of long term use is lacking.
What the study does add is a reason to treat melatonin as something more than candy. It was built for occasional use, and many people now take it every night for years. If that describes you, it is worth raising with a doctor, especially if you have heart disease or risk factors for it.