130,000 patients expose melatonin’s hidden heart failure risk

The most popular sleep supplement in America may be quietly damaging the organ you need most to stay alive.

A study presented at the American Heart Association's Scientific Sessions 2025 tracked 130,828 adults with insomnia over five years. Those who used melatonin for a year or longer were 3.5 times more likely to be hospitalized for heart failure than matched non-users (19.0% vs. 6.6%). They also faced a 90% higher risk of developing heart failure and were nearly twice as likely to die from any cause.

That last number deserves a pause: 7.8% mortality in the melatonin group versus 4.3% in the control group. Over just five years.

The $2.8 billion blind spot

Melatonin is not a drug, at least not in the eyes of the FDA. Under the Dietary Supplement Health and Education Act of 1994 (DSHEA), supplements hit store shelves without proving they are safe or effective. The FDA does not test purity, strength, or composition before a bottle reaches your nightstand.

The consequences are measurable. A JAMA study testing over two dozen melatonin gummies found that nearly all contained more than 10% above the labeled dose. One product had three times the advertised amount. You think you are taking 5mg; you might be swallowing 15mg.

The global melatonin supplement market hit $2.84 billion in 2024. Usage among U.S. adults quintupled over two decades. Nearly 11,000 children ended up in emergency rooms between 2019 and 2022 after unsupervised melatonin ingestion. This is not a niche supplement. It sits in every pharmacy aisle, marketed as harmless as a glass of warm milk.

What the AHA study actually found

Lead researcher Ekenedilichukwu Nnadi, M.D., Chief Resident at SUNY Downstate in Brooklyn, used the TriNetX Global Research Network to analyze electronic health records. The study matched melatonin users against non-users across 40 variables including demographics, existing health conditions, and other medications. Anyone with prior heart failure or concurrent sleep medication use was excluded.

The numbers were stark across every metric. Heart failure diagnosis: 4.6% in melatonin users versus 2.7% in non-users. Heart failure hospitalization: 19.0% versus 6.6%. All-cause mortality: 7.8% versus 4.3%. The 82% elevated risk held even when restricted to patients with two or more prescriptions filled at least 90 days apart, suggesting the effect was not driven by brief or accidental use.

The twist that complicates everything

Here is where the picture fractures. A 2024 study published in The Lancet Diabetes & Endocrinology analyzed three major U.S. cohorts totaling 159,072 participants from the Nurses' Health Study and the Health Professionals Follow-up Study. The pooled hazard ratio for cardiovascular disease among melatonin users was 0.94 (95% CI: 0.83-1.06). Translation: no statistically significant increase in cardiovascular risk.

Even more intriguing, the Lancet study found that among shift workers, melatonin use appeared to reduce the cardiovascular harm typically associated with long-term night shifts (p-interaction = 0.013). The same molecule flagged as dangerous in one study showed protective signals in another.

How do you reconcile 3.5x hospitalization risk with a neutral hazard ratio? Population differences matter. The AHA study focused exclusively on insomnia patients already at elevated baseline risk. The Lancet cohorts included healthier general populations. Melatonin may not cause heart failure; it may accelerate it in people already on the edge.

What you are actually risking tonight

The critical gap is not the science. It is the regulation. In Germany, melatonin above 2mg requires a prescription. In Brazil, it has only been available over the counter since 2021. In the U.S., you can buy 10mg gummies at a gas station, with no dosage standardization, no purity verification, and no required medical consultation.

The AHA researchers were careful to note their study cannot prove cause and effect. But "cannot prove causation" is not the same as "safe to ignore." When sleep and longevity research shows that even 24 extra minutes of quality rest can add disease-free years, the irony sharpens: the supplement millions use to chase better sleep may be stealing the health benefits sleep provides.

If you currently take melatonin nightly, the actionable step is not panic. It is a conversation with your doctor about duration, dosage, and whether your insomnia has a treatable root cause that does not require a supplement the FDA has never validated. The $2.8 billion melatonin industry thrives in the space between "probably fine" and "we actually checked." After 130,000 patient records, that space looks a lot more crowded than anyone expected.