Research on melatonin: a sharp increase in the risk of heart failure, hospitalizations and mortality

Now, alarming findings presented at the American Heart Association’s conference link long-term use of melatonin to a sharp increase in the risk of heart failure, hospitalizations, and even death, revealing a dangerous gap between what is perceived as an innocent supplement and possible health consequences.

Melatonin is a hormone that is produced naturally in the brain, mainly in the pineal gland, and serves as one of the central regulators of the biological clock. The body secretes it during the hours of darkness, its levels increase towards bedtime, and with the morning light they decrease.

It does not act as a classic sleeping pill that puts the brain to sleep, but signals to the nervous system that night time has come. Despite this, in practice quite a few users take it over time to fall asleep, sometimes as a substitute for seeing a doctor or as a solution that is experienced as available, cheap and safe.

Eyal, 35 years old, has been suffering from insomnia since the Iron Swords War. According to him, he started taking melatonin after a friend recommended him gummies that she ordered online. “I started with a really low dose of 3 milligrams,” he says.

“When that didn’t work, I went up to two candies a day, and at some point that didn’t help either and I reached the maximum dose of 10 mg. The beginning is always good, you feel tired within half an hour, but after a week it stops having an effect. You keep taking more and more and it doesn’t help, then I started adding sleeping pills.”

Efrat, 32, an intensive care nurse who works night shifts in one of the large hospitals in the center, describes a similar reality. “I can’t stop,” she says.

“I order the melatonin once every two months from the Rabbi. I admit that I exceed the usual doses, otherwise it just doesn’t work. I don’t want to start taking sleeping pills at my age, and in the meantime I’m managing with it. But I admit that I have concerns about the American study. As long as it’s allowed in Israel, I’ll keep buying.”

A 90% increase in the risk of heart failure

Against the public perception of melatonin as a relatively innocent substance, data arrived in November 2025 that caused concern. At the scientific conference of the American Heart Association, an abstract published in the journal Circulation was presented in which the researchers analyzed the medical records of more than 130,000 adults who suffered from chronic insomnia over 5 years. Using melatonin for a year or more has been linked to a 90% increase in the risk of heart failure.

In the same group, a 3.5 times higher risk of hospitalization due to heart failure was observed, and an increase in mortality from any cause, with a 2 times higher risk compared to a control group, 7.8% compared to 4.3%.

Along with the data, the researchers emphasized that this is a preliminary observational study and that it is possible that the sleep disorders themselves, underlying illnesses, depression, anxiety or the use of other medications, contributed to the cardiac risk. However, the very appearance of this signal at a conference of the American Heart Association sharpens the gap between the widespread use of melatonin as a dietary supplement and the partial knowledge of the consequences of prolonged intake.

Another problem is the quality of the product. Since melatonin is sold in the United States as a dietary supplement, control over the content of the substance and actual dosage is more limited. Previous studies have shown considerable deviations between the amount declared on the packaging and the amount actually found, sometimes in significant overdoses. For an Israeli consumer who orders the product by mail and takes it independently, this means uncertainty about what is entering the body.

The Ministry of Health responded: “In Israel, like many countries around the world, melatonin is marketed as an active ingredient in medicines that can only be obtained with a doctor’s prescription. The Ministry of Health constantly warns the public about the dangers of buying medicines outside of the legal marketing channel and calls on the public to buy medicines only in places approved for this, such as pharmacies and pharmacy chains, and to avoid buying medicines through social networks and unfamiliar websites.”