This common bedtime supplement might be good for sleep, but it can put our hearts at risk

Melatonin supplements are often seen as a gentle solution for sleepless nights, a “natural” fix to reset the body’s internal clock. But new research presented at the American Heart Association’s Scientific Sessions 2025 is raising alarms about its long-term safety. A five-year review of more than 130,000 adults with chronic insomnia revealed that those who used melatonin for over a year were significantly more likely to develop heart failure, require hospitalisation, or die from any cause compared to non-users. While the findings don’t confirm that melatonin directly causes heart problems, they raise critical questions about the supplement’s long-term effects on cardiovascular health. The study urges a closer look at what’s marketed as a harmless sleep remedy, and whether “natural” always means safe.

Researchers analysed data from 130,828 adults with chronic insomnia, tracking their health over five years. Those who used melatonin for a year or longer showed a 90% higher risk of developing heart failure and were 3.5 times more likely to be hospitalised for it. They were also nearly twice as likely to die from any cause during the study period. These results were consistent even after accounting for other factors like age, blood pressure, and medications.

Melatonin is a hormone that helps control the sleep-wake cycle. The body naturally produces it in response to darkness, but supplements are used to treat insomnia or jet lag. In countries like the US, it’s sold freely as an over-the-counter pill, often without dosage regulation or quality checks. Many people assume that because it’s “natural,” it’s safe, a belief that may now need rethinking.

Lead author Dr Ekenedilichukwu Nnadi from SUNY Downstate in New York noted that the findings suggest melatonin “may not be as harmless as commonly assumed.” Experts like Dr Marie-Pierre St-Onge from Columbia University echoed the concern, highlighting that melatonin isn’t actually approved for long-term insomnia treatment in the US Despite this, many continue using it for months or years, often without medical guidance.

Researchers caution that the study doesn’t prove melatonin causes heart failure. It’s possible that underlying insomnia severity, depression, or anxiety, which are themselves linked to heart risk, might play a role. However, the consistent patterns observed across such a large dataset suggest the need for deeper investigation into how melatonin interacts with cardiovascular systems over time.

Unlike prescription drugs, melatonin supplements vary in strength and purity. A tablet labelled as “3 mg” might actually contain much more or less, depending on the brand. This lack of regulation raises questions about dosage safety, especially for long-term use. In countries where melatonin requires a prescription, such as the UK, physicians generally avoid recommending it for chronic insomnia.

The findings underline an important message: better sleep should not come at the cost of heart health. Experts recommend exploring non-drug options first, like improving sleep hygiene, following a consistent bedtime, and limiting screen time before bed. If supplements are necessary, short-term and supervised use is key. More rigorous studies are still needed to confirm these findings, but until then, caution may be the best policy.

This article is based on preliminary findings presented at the American Heart Association’s Scientific Sessions 2025. The study has not yet been peer-reviewed. The information is for educational purposes only and should not replace medical advice. Always consult a healthcare professional before starting or continuing any supplement.