Melatonin and The Heart: In the News

Many people were really surprised to hear about possible negative effects of melatonin on the heart, because it is so widely used, and there is so much research on its benefits.

Melatonin is a natural hormone made in the pineal gland in the brain, in response to darkness. It is chronobiotic, setting and restoring healthy sleep cycles. It helps the body wind down in preparation for sleep. 

Melatonin is a popular sleep aid supplement, and research shows adults over 55 benefit most, probably because melatonin production declines with age. Unlike many sleep medications, melatonin is not addictive, although it can trigger minor side effects such as grogginess, headaches, and nightmares in some users.

In addition to its chronobiotic properties, melatonin possesses antioxidant, anti-inflammatory, and immune-supporting qualities, which can benefit the whole body.

Recent research has expanded interest in melatonin’s effects on cardiovascular health, particularly heart failure. Scientists have been exploring whether melatonin supplementation could benefit cardiac function. Some research suggests melatonin might reduce oxidative stress, improve endothelial (blood vessel lining) function, and potentially modulate blood pressure: factors relevant to risk of heart failure.

A 2018 review of research in the Journal Molecules noted that “Substantial evidence supports the importance of endogenous melatonin in cardiovascular health and the benefits of melatonin supplementation in various cardiac pathologies and cardiometabolic disorders” and that “Melatonin plays a crucial role in major pathological processes associated with heart failure including ischemic injury, oxidative stress, apoptosis, and cardiac remodelling”.

It concluded that, “while few clinical studies have investigated the role of melatonin in the context of heart failure, current findings from experimental studies support the potential use of melatonin as preventive and adjunctive curative therapy in heart failure.”

Following that, a systematic review and meta-analysis in March 2025 came to the conclusion that “melatonin, by increasing psychologic parameters and cardiac potency, could be advised as a novel drug for treatment and palliating heart failure patients.”

So it was a surprise when, at the American Heart Association’s Scientific Sessions in November 2025, preliminary information was shared that long-term melatonin use (defined as 5 years or more), for insomnia was associated with a higher hazard of heart failure (HF), an increase in HF hospitalizations and a doubling of all-cause mortality, over five years, according to a large, multinational observational study.

Do note that this showed an association between long-term melatonin use and higher risk of heart failure—but did not prove causation. This information had not been peer reviewed or published when the news hit the media. In fact, the organization said that the study “cannot prove a direct cause-and-effect relationship”. Experts argue that a more likely explanation of the results is that sleep apnea, worse insomnia, anxiety, depression, or other sleep-aid use are driving the increased risk, rather than melatonin itself.

This is how research goes forward, learning about a subject, knowing that contradictory information arises, and then doing more research to clarify the confounding factors. And this is why experts are not suggesting that melatonin is a definite danger. This one study had significant limitations, was not designed to be able to prove cause and effect, and contradicts previous studies that indicate positives for heart health. As one physician researcher from Duke University said, this study “left me with a lot more questions than answers.”

For people who take it occasionally and have no significant cardiac risk factors, melatonin still looks like a reasonable option. But if you’re taking it nightly for a year or more, or have heart disease, you should talk to your health care provider.