Is Melatonin Safe Long-Term? What the 2025 Heart Study Means

Melatonin has been the world's most popular sleep supplement for over a decade. It's available over the counter in most countries, it's marketed as natural and safe, and millions of people take it every single night without a second thought.

But a growing body of evidence is raising questions that deserve honest, direct answers. Is nightly melatonin actually safe long-term? What does the latest research show? And if the risk profile is changing, what should you do about it?

This article breaks down the current evidence — including the study that made headlines in late 2025 — and gives you a clear, evidence-based framework for making an informed decision.

The 2025 AHA Heart Study: What It Actually Found

In November 2025, researchers presented findings at the American Heart Association (AHA) Scientific Sessions that generated significant media coverage and public concern. Here's what the study actually showed:

The Key Findings

Important Context

Before drawing conclusions, several important caveats must be acknowledged:

That said, a 90% increase in risk is a substantial signal. Even accounting for confounders, cardiologists have noted that this warrants serious follow-up research and should give chronic users reason to reassess their nightly habit.

The JAMA Labeling Problem: You Don't Know What You're Taking

The AHA study becomes even more concerning when paired with a 2023 study published in JAMA (Journal of the American Medical Association) that tested the actual melatonin content of popular supplements.

The findings were alarming:

This means that a person taking what they believe is 5 mg of melatonin nightly could actually be consuming 17 mg or more — every night, for months or years. When evaluating the cardiovascular risk from the AHA study, the actual dose exposure may be far higher than participants believed.

Because melatonin is classified as a dietary supplement in the United States (not a drug), it's not subject to the same FDA manufacturing standards, purity requirements, or dosage accuracy regulations that apply to pharmaceutical medications. There is essentially no guarantee that what's on the label matches what's in the bottle.

Known Side Effects of Melatonin

Even setting aside the emerging cardiovascular data, melatonin's side effect profile is more extensive than most people realize:

Common Side Effects

Less Common but Notable Concerns

The Pediatric Crisis: 530% Increase in Poisoning Calls

One of the most concerning trends in the melatonin landscape involves children. Over the past decade, calls to poison control centres related to pediatric melatonin ingestion have increased by approximately 530%.

Several factors drive this crisis:

While acute melatonin overdose is rarely life-threatening, it can cause severe drowsiness, digestive upset, and in some cases, hospitalisation — particularly in young children or when combined with inaccurate labeling.

Putting It in Context: When Melatonin IS Appropriate

This article isn't arguing that melatonin is universally dangerous. The evidence supports melatonin use in specific, short-term situations:

In all of these appropriate use cases, the recommended approach is a low dose (0.3–0.5 mg) at the physiological level, taken 30–60 minutes before desired sleep time, for a limited duration. The concern isn't with melatonin as a tool — it's with the way most people actually use it: high doses, every night, for months or years, with products they can't trust to be accurately labeled.

The Alternative Approach: Support Your Body's Natural Melatonin

If chronic melatonin supplementation carries risks, what's the alternative for people who genuinely struggle with sleep?

The answer lies in understanding why your body isn't producing enough melatonin on its own — and addressing that root cause rather than adding external hormones.

The Cortisol-Melatonin Axis

In a healthy circadian rhythm, cortisol (your stress and wakefulness hormone) peaks in the morning and gradually declines throughout the day. As cortisol drops in the evening, melatonin rises — signaling your body that it's time to sleep.

For most chronic poor sleepers, this axis is disrupted. Cortisol remains elevated into the evening due to stress, screen exposure, irregular schedules, or chronic inflammation. With cortisol still elevated, melatonin can't rise adequately — and the supplement temporarily masks this fundamental dysfunction.

The most sustainable approach is to fix the cortisol rhythm, which then allows natural melatonin production to resume.

How Grounding (Earthing) Addresses the Root Cause

Grounding — maintaining physical contact with the Earth's electrical charge, either directly (barefoot on soil) or through conductive equipment like grounding sheets — has demonstrated measurable effects on cortisol regulation.

The Ghaly and Teplitz (2004) study, published in the Journal of Alternative and Complementary Medicine, measured 24-hour cortisol profiles in subjects sleeping grounded versus ungrounded. The results showed significant normalization of the circadian cortisol rhythm in the grounded group — specifically, cortisol dropped more appropriately in the evening and night.

This is directly relevant to the melatonin question: if cortisol normalizes in the evening, the biological conditions for natural melatonin production are restored. You don't need to supplement what your body can produce on its own when the suppressive factor (cortisol) is addressed.

A 2025 double-blind, placebo-controlled study provided further evidence, demonstrating measurable sleep quality improvements in grounded participants versus a sham-grounded control group. The double-blind design is particularly significant because it eliminates the placebo effect — a major confounder in sleep research.

How Grounding Sheets Work

A grounding sheet is a flat sheet woven with conductive stainless steel fibres that connect to the earth port of your electrical outlet via a grounding cord. No electricity flows through the cord — only the Earth's natural electrical charge.

You place the grounding sheet on your mattress and sleep in contact with it. A natural-fibre fitted sheet (cotton or linen) can be placed on top without blocking conductivity. While you sleep, free electrons from the Earth transfer to your body, helping to:

To confirm your outlet's earth port is properly wired, a socket tester is available separately.

The key advantage over melatonin supplements: grounding doesn't cause tolerance, doesn't carry the labeling uncertainty of supplements, and doesn't introduce an external hormone into your system. It works with your biology rather than overriding it.

Explore grounding sheets | Grounding pillowcases

Melatonin Supplements vs. Supporting Natural Production: A Comparison

What You Should Do Now

Based on the current evidence, here's a straightforward framework:

Frequently Asked Questions

Is melatonin safe to take every night?

Short-term nightly use (a few weeks) at physiological doses (0.3–0.5 mg) is generally considered safe. However, chronic nightly use for months or years raises emerging concerns, including a preliminary 2025 AHA study linking 12+ months of use to approximately 90% higher heart failure risk. The safety of long-term nightly use at the doses found in most commercial products (5–10 mg) has not been established.

What did the 2025 melatonin heart study find?

Researchers presented data at the November 2025 American Heart Association Scientific Sessions showing that adults who used melatonin nightly for 12 or more months had approximately 90% higher risk of heart failure over a five-year follow-up compared to non-users. The findings are preliminary (presented at a conference, not yet fully peer-reviewed in a journal) and represent an association, not proven causation.

Can melatonin cause heart problems?

The evidence is not yet conclusive, but the AHA 2025 data represents a significant signal that long-term use may be associated with increased cardiovascular risk. This is preliminary research and needs replication and peer review. However, the size of the association (approximately 90% higher risk) has prompted many sleep specialists to recommend that chronic users reconsider nightly supplementation.

How much melatonin is actually in my supplement?

According to a 2023 JAMA study, 88% of melatonin products are mislabeled, with some containing up to 347% more melatonin than stated. Because melatonin is regulated as a supplement (not a drug), manufacturers aren't held to pharmaceutical-grade accuracy. You may be consuming significantly more or less than you think.

What are safer alternatives to melatonin for long-term sleep support?

The most evidence-backed alternatives address the root cause of poor sleep (cortisol dysregulation) rather than supplementing a hormone. Grounding sheets normalize cortisol rhythms to support natural melatonin production (Ghaly & Teplitz 2004; 2025 double-blind study). Morning bright light exposure and evening light restriction recalibrate circadian timing. Magnesium glycinate supports nervous system relaxation without causing tolerance.

Should I stop taking melatonin immediately?

A gradual taper is recommended over stopping abruptly, to minimize rebound insomnia. Our step-by-step tapering guide outlines a 4-week protocol. If you have specific health concerns, discuss your situation with your healthcare provider.

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