When you struggle with sleep, reaching for an over-the-counter sleep aid such as melatonin might feel like a simple solution. But recent research is shining a bright light on a potential downside: long-term routine use of the supplement may be associated with a higher risk of heart problems. 

For American adults who increasingly rely on melatonin for sleep, understanding this link is more important than ever. In this article we’ll explore what the latest study found, how melatonin works, and what it means for your heart health.

What is Melatonin?

is a hormone produced naturally by the pineal gland in the brain. It helps regulate your sleep-wake cycle (circadian rhythm) by rising in the evening to promote sleep, then falling in the morning.

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As a supplement, melatonin is commonly used in the United States (as an over-the-counter product) to help with insomnia, jet lag, or simply falling asleep faster.

Why this issue is now relevant

In recent years the use of melatonin supplements exploded. Many view it as a “natural”, low-risk sleep aid. However, despite its popularity, the long-term effects, especially on heart health haven’t been fully understood. A newly reported large-scale observational study now raises questions about whether taking melatonin for extended periods (a year or more) might affect the cardiovascular system.

Given how common sleeplessness and insomnia are among U.S. adults, the implications are considerable: if a widely used supplement carries risks, we need to understand them.

Main Explanation

How Melatonin Works in the Body

• Melatonin helps signal to your body that it’s nighttime, enabling physiological changes tied to sleep.
• Beyond sleep, melatonin interacts with many systems: immune modulation, inflammation, oxidative stress, and even cell-death pathways have been linked to it.
• Because melatonin is available as a supplement in different doses, formulations (immediate-release vs extended release) and with minimal regulation (in the U.S.), its effects may vary widely.

Key Study Findings: Long-Term Use & Heart Health

A large observational cohort study (presented at the  2025 Scientific Sessions) used data from over 130,000 adults with insomnia.  Here are the headline findings:

• Among those who used melatonin for one year or more, there was about a 90% higher risk of developing heart failure over five years compared to matched insomnia patients who did not use melatonin.
• Hospitalization related to heart failure was about 3.5 times higher among the long-term melatonin users (19% versus 7% in controls).
• Death from any cause was approximately double among the melatonin users (8% vs ~4% in non-users) over five years.
• These associations held even after matching for demographics, comorbidities, body-mass index, other medications, and health-care utilization.

What These Results Don’t Prove (and Why That Matters)

• Not causation
  The study is observational. It shows a strong association, but it cannot definitively prove that melatonin caused heart failure.
• Confounding factors
  For example, people with more severe insomnia may be more likely to use melatonin and also more likely to have underlying cardiovascular risks (sleep apnea, stress, obesity). These factors may contribute to both melatonin use and heart problems.
• Over-the-counter use not fully captured
  In the U.S. melatonin is OTC; many users may not be recorded in prescription databases. This may misclassify some users as non-users, which affects accuracy.
• Dosage, formulation and duration vary
  The study did not fully parse out how dose or formulation (e.g., 1 mg vs 10 mg, fast vs slow release) may impact risk.

Potential Mechanisms (How Might Melatonin Influence Heart Health?)

Researchers and experts propose several possibilities:

• Disruption of circadian rhythm
  While melatonin is meant to support the internal clock, chronically altering natural melatonin rhythms might impair cardiovascular regulation (blood pressure, heart rate variability).
• Hormonal and metabolic effects
  Since melatonin interacts with other hormonal systems (immune, metabolic, inflammatory), long-term excess or misuse might tip balances in ways that stress the heart.
• Underlying insomnia as a driver
  Sleep disorders themselves (insomnia, obstructive sleep apnea) are linked to cardiovascular disease. If melatonin use is a marker for chronic insomnia, the risk might reflect the insomnia more than the supplement.
• Supplement regulation issues
  Because melatonin is regulated as a supplement—not a drug—in the U.S., dosage, purity and formulation consistency vary. That variability might mean some users take more than intended or combine with other sleep aids, adding risk.

Practical Context for U.S. Adults

Many Americans turn to melatonin for short-term sleep help (jet lag, shift changes, occasional insomnia). Short-term, low-dose use has been considered relatively safe. The concern arises when melatonin becomes a long-term nightly crutch rather than part of a broader sleep health plan.

For individuals with existing heart or metabolic risk factors (hypertension, diabetes, obesity, coronary disease), introducing a supplement with uncertain long-term cardiac impact warrants additional caution.

Good sleep hygiene (dark room, consistent bedtime, avoiding screens before bed, limiting caffeine/alcohol) and addressing underlying sleep disorders (such as sleep apnea) remain foundational.

Analysis & Insight

Expert Opinions

Cardiologists and sleep medicine experts are paying attention. For example,  (not part of the study) noted like this:

“While the study shows an association and not a direct cause-and-effect relationship … the consistency and significance of the increased risks are noteworthy.”
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Sleep medicine specialists stress that melatonin is not approved by the  (FDA) for long-term treatment of insomnia and is best used under guidance.

Implications for Practice

• Clinicians should ask about melatonin use when assessing patients with insomnia, particularly if there are underlying cardiovascular risks.
• Patients should not assume “natural = risk-free.” Even over-the-counter supplements can carry significant associations.
• Researchers should follow up with randomized controlled trials (RCTs) or prospective cohorts to determine causation, dosage thresholds and mechanism. The current study uses real-world data and serves as a strong signal.

Thinking Critically

Because the study excluded patients who were already diagnosed with heart failure or on other sleep medications, it focused on a somewhat healthier on-paper population yet still found elevated risk among melatonin users.

It raises a “chicken-or-egg” question: Did melatonin use drive heart risk, or did early heart/vascular changes (manifesting in sleep disruption) prompt melatonin use? Either way: the link is meaningful.

And for U.S. readers, the regulatory environment matters: melatonin duties and oversight differ from prescription drugs; brands differ in quality and dosing. That adds complexity to interpreting any risk.

Conclusion

A recent large observational study suggests that adults who used melatonin supplements for one year or more had about a 90% greater risk of developing heart failure over five years, plus higher hospitalization and mortality rates.

It does not prove that long-term melatonin use causes heart disease, but the association is strong enough that it should prompt caution and conversation between patients and healthcare providers.

If you are using it nightly for months or years, especially with other heart or sleep issues, it’s time to re-examine whether this is the best strategy. Seek guidance, and consider addressing sleep health more broadly (sleep hygiene, sleep disorder evaluation, lifestyle).

A takeaway message: just because something is “natural” or over-the-counter doesn’t guarantee safety for long-term use, particularly when it intersects with cardiovascular health.

And if you’ve been using melatonin regularly, talk with your physician about your sleep patterns, heart health, and whether you might benefit from alternative approaches (behavioral sleep therapy, evaluation for sleep apnea) instead of indefinite supplement use.