Melatonin & Heart Failure 2025 – What You Should Know

Why this matters

If you or someone you’re caring for has heart failure (or is at high risk), you may be asking: “Is taking melatonin safe? Could it help my heart or hurt it?” This article walks you through the science, the uncertainties, how to interpret the data, and what to do in practice. I’ll point out where data is strong, where it’s weak, and where you should ask your cardiologist or sleep physician for guidance.

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1. Understanding the players: heart failure and melatonin

What is heart failure?

Heart failure (HF) isn’t simply “weak heart” in a generic sense. It’s a clinical syndrome where the heart cannot pump (or fill) efficiently enough to meet the body’s demands. That leads to symptoms like fatigue, breathlessness, fluid retention. It is broadly classified into:

• Heart failure with reduced ejection fraction (HFrEF)
• Heart failure with preserved ejection fraction (HFpEF)
  And each has different underlying causes (ischaemic heart disease, hypertension, valvular disease, etc.).

When discussing melatonin’s role, much of the animal/early human data centres on HFrEF or models of pressure/volume overload.

What is melatonin?

Melatonin (N-acetyl‐5‐methoxytryptamine) is a hormone produced primarily by the pineal gland. It helps regulate circadian rhythm (sleep-wake cycles) and has wider roles: antioxidant, anti‐inflammatory, metabolic modulation.

As a supplement it’s often taken for insomnia, jet lag, or circadian rhythm disorders. But in the context of cardiovascular disease, we need to separate what we know about endogenous melatonin biology from what we know about taking extra melatonin as a pill.

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2. Mechanistic & pre-clinical evidence: why it might help the heart

Here’s where things look promising (but still early). What this really means is: there are plausible pathways by which melatonin could protect cardiac structure and function.

Key mechanisms

• Antioxidant/anti‐inflammatory effects: Melatonin reduces reactive oxygen species, lowers inflammatory cytokines (e.g., IL‐6, TNF-α) in cardiac models.
• Anti‐fibrotic action: In non-ischaemic heart failure models, melatonin reduces extra-cellular matrix deposition (collagen/fibrosis) in the heart muscle.
• Mitochondrial/energetic support: Some studies show melatonin enhances mitochondrial biogenesis and improves metabolic reserve in failing myocardium.
• Neurohormonal modulation: Because heart failure involves activation of the renin‐angiotensin‐aldosterone system (RAAS), sympathetic overactivity and so on, melatonin’s modulation of these pathways has been proposed.

Pre–clinical/early human data

For example, one randomized trial design (MeHR trial) enrolled ~90 outpatients with HFrEF to assess 10 mg melatonin vs placebo over 24 weeks, measuring echocardiography, NT-proBNP, muscle mass, etc.

Systematic reviews note that melatonin receptors (MT1/MT2) are implicated in cardiac/vessel regulation, and low endogenous melatonin levels were associated with worse outcomes in heart failure.

So what can we conclude from this?

• The biological rationale: solid. We have pathways, animal models, early human signals, to support a potential benefit.
• But there’s a big caveat: dose, formulation, timing, patient population in these experiments often differ from what a typical patient might do as “take melatonin at night for sleep.”
• Therefore, we cannot say melatonin is established therapy for heart failure yet.

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3. Human observational signals: caution flags

Here’s where things become complicated—and important. Evidence from large real-world populations raises potential risks when melatonin is used long-term. What this truly underscores is: plausible benefit does not guarantee safety or efficacy in the clinic.

Recent observational study

A very recent large observational study (reported late 2025) looked at adults with chronic insomnia, over five years, and found:

• Among those taking melatonin for ≥ 12 months, the incidence of new heart failure was ~4.6% vs ~2.7% in non-users (≈ 90% higher risk).
• Those users were ~3.5 times more likely to be hospitalized for heart failure (19.0% vs 6.6%).
• Mortality (any cause) over five years was also higher in melatonin users (~7.8% vs 4.3%).

Why this doesn’t mean “melatonin causes heart failure”

• It is observational: correlation not causation. The study authors and independent experts are clear about this.
• Confounding: People taking melatonin long‐term may already have insomnia, mental health issues, other sleep disorders (like obstructive sleep apnea) which themselves increase cardiovascular risk.
• Dose/formulation/duration: Over‐the‐counter vs prescription, actual usage patterns are unclear. Some users may have been misclassified.

Implications

• We should view these findings as warning signs.
• If you have heart failure, or are at high risk (hypertension, coronary disease, diabetes), then taking melatonin chronically warrants conversation with your cardiologist or sleep physician.
• At minimum: keep use minimal, monitor cardiac symptoms, avoid assuming “natural = safe” indefinitely.

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4. Reconciling the opposing signals: benefit vs risk

This is the heart of the issue (no pun intended). If melatonin has biologic plausibility for benefit, why the concerning observational data?

Possible explanations

1. Beneficial when used short term or in a controlled way, harmful when used long term/unmonitored. The mechanistic data often involve defined doses/shorter durations; the observational data cover longer term, uncontrolled use.
2. Underlying risk may drive both melatonin use and heart failure (reverse causation). E.g., people with poor sleep, sleep apnea, undiagnosed cardiac dysfunction may self-medicate with melatonin, and their heart condition (not melatonin) leads to worse outcomes.
3. Dose/timing issues: High-dose, irregular administration might carry different risk compared to low-dose, well‐timed use.
4. Heterogeneity of heart failure populations: HFrEF vs HFpEF may respond differently; likewise, comorbidities (renal disease, obesity, etc) may modify effect.
5. Supplement regulation/quality issues: Over‐the‐counter melatonin is not uniformly regulated; product variability could mean some users receive higher than expected doses or mixed ingredients. The observational study flagged this as a limitation.

What I conclude from those points

• Melatonin is not ready to be a standard heart‐failure therapy.
• If a patient with heart failure is considering melatonin (for sleep or otherwise), we need to tailor decision making: what’s their cardiac status, what are other sleep strategies, what dose/timing is being used?
• At this moment, more moderate and pragmatic approach: treat melatonin like any drug: consider indication, monitor effects, minimise duration if possible.

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5. Practical guidance for patients & clinicians

What difference does this make practically? Here are actionable takeaways—tailored for someone with heart failure or at risk.

For patients

• If you have heart failure (or reduced ejection fraction) and you’re using melatonin nightly: schedule a discussion with your cardiologist or sleep specialist.
• Sleep hygiene first: address the root causes of insomnia—fluid overload, sleep apnea (common in heart failure), restless legs, medications, anxiety. Supplements should not be the first fix.
• If you use melatonin:
  • Use the lowest effective dose. The mechanistic studies often looked at defined doses (e.g., 10 mg) but sleep doses are often lower (1–5 mg).
  • Use for a defined period, not indefinitely, unless there’s good reason and specialist oversight.
  • Be alert to worsening heart symptoms: increasing breathlessness, fluid retention, fatigue, palpitations.
  • Check other interactions: melatonin may affect blood pressure medications, and sleep disorders can worsen heart failure.

For clinicians

• Don’t assume over‐the‐counter melatonin is entirely benign—especially in a heart failure patient. This recent observational data suggests potential risk.
• Consider assessing endogenous melatonin levels or circadian rhythm disturbances in HF patients with sleep complaints (though these are not standard yet).
• Prioritize evidence‐based sleep interventions (e.g., cognitive behavioural therapy for insomnia, screening/treating obstructive sleep apnea) before relying on melatonin only.
• Monitor heart failure patients who are on long-term melatonin: note hospitalization rates, symptom changes, NT-proBNP if relevant, ejection fraction changes.
• Educate patients: “natural” product ≠ no risk. Emphasize product quality (look for third‐party testing) and avoid high doses over long durations unless data supports it.

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6. Gaps in the research & what to watch for

Here are key areas where more info is needed—and where future trials might clarify things.

• Randomised controlled trials in heart failure patients: We saw the design for such a trial (MeHR) but we don’t yet have large‐scale, long-term outcome data.
• Distinction between types of heart failure (HFrEF vs HFpEF): Mechanisms differ; melatonin’s role may differ accordingly.
• Long‐term safety of melatonin use in cardiovascular populations: The observational data suggest risks if used for ≥12 months, but causality and dose‐response remain unclear.
• Optimal dose/timing/formulation: Immediate release vs extended; night time vs other; how these affect cardiac outcomes.
• Interaction with other heart failure therapies and comorbidities: Do beta‐blockers, RAAS inhibitors, SGLT2 inhibitors modify melatonin’s effect?
• Endogenous melatonin levels as a prognostic marker in heart failure: Some studies show low melatonin levels correlate with worse prognosis.
• Quality assurance of melatonin supplements: Especially relevant in over-the-counter markets where dosing and purity vary.

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7. Summary table of evidence (benefits vs risks)

Evidence Type	Key Findings	Strength of Evidence
Mechanistic/animal studies	Antioxidant, anti‐fibrotic, mitochondrial effects of melatonin in cardiac models	Moderate (animal/human‐early)
Small human studies	Lower endogenous melatonin linked to worse HF; small supplementation studies	Limited
Large observational cohort	Long‐term melatonin use (≥12 m) in insomnia patients associated with ↑ HF risk	Emerging, associative only
Randomised trials in HF patients	Trial underway (e.g., MeHR)	Not yet definitive

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8. What this means for you (if you have heart failure or high risk)

• Treat sleep problems seriously—they may impact your heart directly (via sympathetic activation, poor oxygenation, arrhythmias).
• If you’re using melatonin or considering it:
  • Confirm there’s an indication (insomnia, circadian rhythm issue) and that other root causes (sleep apnea, fluid overload) are addressed.
  • Use it as part of a broader plan, not stand‐alone “heart recovery pill”.
• Stay alert to evolving research—2025/2026 will likely bring better trials and clearer guidance.
• Share this conversation with your healthcare team—ask: “Given my heart condition, is melatonin safe/beneficial for me? For how long? At what dose?”

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10. Final take-home message

Here’s a plain spoken takeaway: If you have heart failure, melatonin might help—but we don’t know enough to rely on it safely yet. Worse, long‐term use in some data is linked to higher heart failure events. So be cautious. Use the sleep hormone wisely, not casually. Sleep is important, your heart is important, but the link between melatonin supplements and heart health is still in flux.

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