Melatonin is the most popular sleep supplement in the world. It’s available without a prescription in most countries. It’s marketed as “natural.” It’s given to children. And in November 2025, a study presented at the American Heart Association’s Scientific Sessions found that adults with chronic insomnia who took melatonin for more than a year had nearly double the risk of heart failure, were 3.5 times more likely to be hospitalised for heart failure, and were twice as likely to die from any cause — compared to insomnia patients who didn’t use melatonin.
That’s not a typo. The numbers were large, the study population was large (over 130,000 adults), and the findings were consistent across multiple sensitivity analyses. The research hasn’t yet been peer-reviewed, and it cannot prove melatonin causes heart failure. But the association was strong enough to prompt leading sleep researchers to call for a serious reassessment of how casually melatonin is used.
This article breaks down what the study actually found, what it means for people currently taking melatonin, and — most importantly — what to do instead when the real question isn’t whether melatonin is safe, but why your body needs it in the first place.
What Melatonin Is — and What It Isn’t
Melatonin is a hormone produced naturally by the pineal gland in response to darkness. It doesn’t make you sleep — it signals to your body that it’s time to sleep. Think of it as a dimmer switch, not an off button. Natural melatonin rises in the evening as light fades, peaks in the first few hours of sleep, and gradually declines toward morning.
Supplemental melatonin is a synthetic copy of this hormone. In the United States, it’s classified as a dietary supplement, which means it doesn’t require FDA approval for quality, dosage accuracy, or safety testing. Independent analyses have found that the actual melatonin content of supplements varies from 83% less to 478% more than what’s listed on the label. Some products also contain serotonin — an active neurotransmitter that shouldn’t be in an over-the-counter supplement.
This quality control problem is unique to the supplement industry. Prescription medications are held to strict manufacturing standards. Melatonin supplements are not — and the person taking them has no way of knowing what they’re actually consuming on any given night.
This matters because most people take melatonin as if it’s a harmless vitamin. They take it nightly, often at doses far higher than the body naturally produces (the body makes about 0.1–0.3 mg per night; supplements commonly contain 3–10 mg), and they do so for months or years without questioning whether there might be downstream consequences.
What the 2025 AHA Study Found
The study, led by researchers at SUNY Downstate, used data from the TriNetX Global Research Network — an international database of de-identified medical records. They identified 130,828 adults diagnosed with chronic insomnia and divided them into two groups: 65,414 who had documented melatonin use for at least one year, and 65,414 matched controls with insomnia who had never used melatonin.
Over five years of follow-up:
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Incident heart failure occurred in 4.6% of melatonin users versus 2.7% of non-users — a 90% higher risk
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Heart failure hospitalisation occurred in 19% of melatonin users versus 6.6% of non-users — a 3.4-fold increase
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All-cause mortality was 7.8% in melatonin users versus 4.3% in non-users — roughly double
The researchers controlled for over 40 baseline variables including demographics, comorbidities, medications, vital signs, and healthcare utilisation. The results held in sensitivity analyses requiring at least two melatonin prescriptions filled 90 days apart.
What This Does — and Doesn’t — Mean
This study shows an association, not causation. Several important caveats apply:
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The database includes countries where melatonin requires a prescription (like the UK) and countries where it’s over-the-counter (like the US). American OTC users would appear in the “non-melatonin” group, potentially diluting the true control population.
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People who use melatonin long-term may have more severe insomnia, more underlying health conditions, or more undiagnosed sleep disorders — any of which could independently increase heart failure risk.
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The study hasn’t been peer-reviewed or published in a journal yet. The findings are preliminary.
However, the researchers and several independent experts raised a critical point: insomnia itself may be an early symptom of heart failure. People with emerging heart failure often develop sleep disturbances before the condition is formally diagnosed. Melatonin use might be a marker for people whose insomnia is signalling an underlying cardiac problem — not the cause of the cardiac problem itself.
Either way, the study reinforces a principle that applies regardless of whether melatonin is directly harmful: if your body can’t sleep without supplemental melatonin, the question isn’t “which dose should I take?” It’s “why isn’t my body making enough melatonin on its own?”
Why Your Body Might Not Be Producing Enough Melatonin
Melatonin production depends on a chain of biological processes, and a disruption at any point reduces the output:
Serotonin depletion. Melatonin is synthesised from serotonin. About 90–95% of the body’s serotonin is produced in the gut. Gut infections — particularly H. pylori, which damages the enterochromaffin cells responsible for serotonin production — directly reduce the raw material available for melatonin synthesis.
Nutrient deficiencies. The conversion of tryptophan to serotonin requires B6. The conversion of serotonin to melatonin requires zinc and darkness. Deficiency in any of these — common in people with gut infections or chronic stress — creates a bottleneck in the production chain.
Circadian disruption. Melatonin release is triggered by darkness and suppressed by light, especially blue-spectrum light. Evening screen use, bright indoor lighting, and irregular sleep timing all weaken the circadian signal that initiates melatonin production.
Age. Melatonin production naturally declines with age. By middle age, many adults produce significantly less than they did in their twenties, which narrows the margin for any additional disruption.
When you take supplemental melatonin without addressing the reason your natural production is low, you’re replacing a signal without fixing the system that generates it. It’s like putting a louder alarm in a building where the fire suppression system is broken — helpful in the moment, but not a solution.
This is also why melatonin often works well initially and then seems to lose its effectiveness over time. The underlying cause — whether it’s a gut infection, a nutrient deficiency, or circadian disruption — continues to worsen. The supplemental melatonin compensates for a while, but eventually the gap between what the body needs and what the supplement provides grows too wide. People respond by increasing the dose, which only delays the reckoning.
If you would like to see how we might be able to help you with this deeper, schedule a free consult here.
What to Do Instead of Long-Term Melatonin
Fix the Circadian Signal
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Morning sunlight within 30 minutes of waking — the most powerful melatonin-timing intervention available
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Dim warm lighting after sunset — reduce blue light exposure from screens and overhead lighting
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Consistent wake time — anchors the circadian clock so the melatonin rise is predictable
Rebuild the Production Chain
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Test and treat gut infections — H. pylori and parasites that damage serotonin-producing cells
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Supplement B6, zinc, and magnesium if deficient — cofactors for the tryptophan-serotonin-melatonin pathway
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Include tryptophan-rich foods and evening carbohydrates to support serotonin production naturally
Use Evidence-Based Alternatives
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L-theanine (200 mg before bed) — calms mental hyperarousal without sedation or morning grogginess
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Glycine (3g before bed) — lowers core temperature and increases deep sleep through a completely different mechanism than melatonin
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Magnesium glycinate (300–400 mg) — supports GABA function and muscle relaxation
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Vagus nerve exercises — shift the nervous system into the parasympathetic state that sleep requires
This article is educational and not medical advice. If you’re currently taking melatonin, consult your healthcare provider before making changes.
When to Seek Professional Help
Seek help if:
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You’ve been taking melatonin nightly for more than 3 months and can’t sleep without it
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Melatonin helped initially but has become less effective over time
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You’re taking 5 mg or more nightly — far above physiological levels
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Sleep problems coexist with digestive symptoms, fatigue, or unexplained nutrient deficiencies
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You have cardiovascular risk factors and are concerned about the 2025 findings
Frequently Asked Questions
Is melatonin safe to take every night?
The 2025 AHA study found that adults who took melatonin for over a year had significantly higher rates of heart failure and all-cause mortality compared to non-users. While this is an association and not proof of causation, it raises concerns about long-term nightly use. Short-term use for jet lag or occasional insomnia appears lower-risk.
What are the long-term side effects of melatonin?
Research suggests potential associations with heart failure, hormonal disruption, and next-day grogginess. Because melatonin is unregulated in the US, supplement quality varies widely — some products contain far more melatonin than labelled, plus undisclosed ingredients like serotonin.
What can I take instead of melatonin for sleep?
L-theanine (200 mg), glycine (3g), and magnesium glycinate (300–400 mg) all have evidence for improving sleep through different mechanisms. More importantly, investigating why your body isn’t producing enough melatonin naturally — gut health, nutrient status, circadian alignment — addresses the root cause.
Why isn’t my body producing enough melatonin?
Common causes include gut infections (H. pylori, parasites) that deplete serotonin, B6 or zinc deficiency blocking the conversion pathway, chronic light exposure suppressing the circadian signal, and age-related production decline.
Should I stop taking melatonin after the 2025 study?
Don’t stop suddenly without consulting your healthcare provider. The study found an association, not causation. However, it reinforces the importance of addressing why you need melatonin rather than relying on it indefinitely as a long-term solution. If you would like to see how we might be able to help you with this deeper, schedule a free consult here.
When to Work With a Sleep Consultant
If you’ve been relying on melatonin and it’s either stopped working or you’re concerned about long-term use, the real solution isn’t finding a better supplement. It’s finding out why your body stopped producing melatonin effectively in the first place — and that investigation often leads to the gut, the nutrient status, and the circadian system.
Riley Jarvis at The Sleep Consultant works with clients to uncover the root biological causes behind chronic sleep issues and build personalised protocols that address every layer — not just the symptoms.
Book a consultation at TheSleepConsultant.com.
