Melatonin and Sleep
An honest, pharmacologically accurate guide to what melatonin does, what it does not do, the dosage reality most people get wrong, and when it is genuinely useful.
What Melatonin Is — and What It Is Not
Melatonin is a hormone produced by the pineal gland in response to darkness. Its primary biological role is to signal the time of day to the circadian system — communicating that it is night. The circadian clock uses this signal to coordinate overnight processes: growth hormone release, core temperature decline, immune cytokine production, and the timing of sleep readiness.
What melatonin actually does
Melatonin shifts the biological clock to align sleep readiness with the correct time of day. It does not directly cause sleep. It acts as a darkness signal to the suprachiasmatic nucleus (the brain’s master clock), telling it that night has begun and sleep processes should be initiated. In a healthy adult in a normal light–dark environment, melatonin begins rising approximately 2 hours before habitual sleep onset — this is called DLMO (Dim Light Melatonin Onset).
The supplement version
Exogenous melatonin (the supplement) works by providing the brain with an artificial darkness signal at the time of ingestion. If you take it 30–60 minutes before your desired bedtime, it provides a phase-advance signal — shifting your biological clock slightly earlier. For jet lag (where your clock is set to the wrong timezone) or delayed sleep phase (where your clock runs late), this is exactly what is needed. For primary insomnia without a circadian component, the evidence is considerably weaker.
The Dosage Reality: Most People Take 10–20 Times Too Much
Most OTC melatonin is sold at 5–10mg. Research consistently shows that 0.5mg is as effective as 5mg for circadian phase shifting and sleep onset improvement, and 0.3mg is closest to the brain’s natural nocturnal melatonin production. Higher doses do not improve efficacy — they produce a pharmacological melatonin flood that may cause morning grogginess and, with chronic high-dose use, may suppress endogenous production. Brzezinski et al. (2005) in Sleep Medicine Reviews confirmed this dose-response relationship. Zhdanova et al. (2001) demonstrated at MIT that 0.3mg produces the same sleep onset reduction as 3mg.
| Dose | Efficacy Rating | Clinical Notes |
|---|---|---|
| 0.1–0.3mg | Effective | Closest to physiological melatonin production. Zhdanova et al. (2001) showed 0.3mg produces the same sleep onset latency reduction as 3mg. Peak endogenous nocturnal melatonin is approximately 0.1–0.3mg equivalent. Difficult to find OTC but splitting tablets achieves this range. |
| 0.5mg | Optimal | Most research-supported therapeutic dose for phase shifting. Equally effective to 5mg in head-to-head studies with fewer side effects (Brzezinski 2005). This is the target dose for most adults. |
| 1–3mg | No added benefit | No more effective than 0.5mg for circadian phase shifting. Commonly available. Some adults use this range without significant next-day impairment. Splitting a 3mg tablet in half or quarters reaches the optimal dose range. |
| 5mg | Excess dose | The most common OTC dose. No efficacy advantage over 0.5mg. Morning grogginess risk increased. This is 10–16 times the dose closest to physiological production. If currently taking 5mg and feeling groggy, reduce dose first. |
| 10mg+ | No clinical basis | No evidence supporting this dose for sleep or circadian benefits. Significant next-day grogginess common. With chronic use, may suppress endogenous melatonin production. Sold in some markets without adequate dosing guidance. |
The Melatonin Dosing Problem — Why Less Is Almost Always More
Standard OTC melatonin dose is 5–10mg — between 10 and 33 times the physiologically active amount. This section explains the dose-response evidence, when melatonin for sleep actually works, the correct timing protocol, and who should not take it — with a citation for every clinical claim.
The Dose-Response Evidence
The definitive study on how much melatonin to take came from Irina Zhdanova and colleagues at MIT. Zhdanova et al. (2001) randomised participants to receive 0.3mg, 1mg, or 3mg melatonin and measured sleep onset latency using polysomnography. The result: 0.3mg produced the same reduction in sleep onset latency as 3mg — a tenfold higher dose — with no dose-dependent improvement in efficacy above 0.3mg. Brzezinski et al. (2005) in Sleep Medicine Reviews extended this finding across multiple studies, confirming that 0.5mg matches 5mg for circadian phase shifting with fewer side effects.
The reason more melatonin does not mean better sleep is pharmacological: melatonin is a timing signal, not a sedative. The melatonin receptor (MT1/MT2) reaches saturation at very low concentrations. Once the receptors are occupied — which happens at 0.3–0.5mg — additional melatonin does not enhance the signal; it simply extends the duration of receptor occupancy, producing a prolonged pharmacological effect that spills into the following morning as grogginess. You are not getting “more sleep” with 10mg; you are getting a melatonin hangover.
When Melatonin Works — and When It Does Not
The evidence for melatonin is specific to its chronobiotic role — shifting a misaligned biological clock. It is not a general sleep enhancer. The Herxheimer & Petrie (2002) Cochrane systematic review found moderate-quality evidence for melatonin in jet lag, particularly for eastward travel crossing 5+ time zones. The American Academy of Sleep Medicine (AASM) 2017 Clinical Practice Guidelines recommend CBT-I as the first-line treatment for chronic insomnia — not melatonin, not sleep medications as initial therapy.
Timing Protocol — When to Take Melatonin
Timing matters more than dose for melatonin efficacy. The correct time depends entirely on your goal. The most common timing mistake is taking melatonin at bedtime when the goal is a circadian phase advance — this is too late to shift the clock effectively.
Who Should Not Take Melatonin Without Medical Guidance
Practical Guidance — How to Use Melatonin Correctly
If you have decided, after checking the contraindications above, that melatonin is appropriate for your situation, follow these evidence-based steps for the lowest effective dose with the best outcome.
When to Take Melatonin — Timing Calculator
Timing matters more than dose for melatonin efficacy. The correct time depends on your goal: gentle sleep onset support, circadian phase advance, or jet lag adjustment. Select your use case below.
For general sleep onset support: take melatonin 30–60 minutes before your desired bedtime. This provides a darkness signal at the intended sleep time.
For phase advance (shifting sleep earlier over days to weeks): take melatonin 5–6 hours before your current natural sleep onset. This is the most effective timing for circadian clock advancement. Note: taking melatonin at bedtime for phase advance is a common mistake — it is too late to shift the clock effectively.
For jet lag: take 0.5mg at the destination’s intended bedtime from night 1 of arrival. Continue for 3–5 nights. Supported by Herxheimer and Petrie (2002) Cochrane systematic review.
Recommended timing
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Recommended dose: 0.5mg. If 0.5mg is unavailable, split a 1mg or 3mg tablet. Always use the lowest effective dose. Consult a pharmacist if you take prescription medications.
When Melatonin Works — and When It Does Not
The evidence for melatonin is specific to its chronobiotic (clock-shifting) role. It is not a general sleep enhancer. The AASM (2017) recommends CBT-I as first-line treatment for chronic insomnia, not melatonin. Understanding this distinction prevents wasted money and false expectations.
Evidence supports melatonin for:
Melatonin is less effective or not appropriate for:
Side Effects by Dose
Melatonin at appropriate doses (0.5mg) has a favourable safety profile in short-term use in healthy adults. Side effects are largely dose-related — the most common issues with melatonin are caused by taking too much, not by the compound itself. This is why starting at 0.5mg and not escalating is the evidence-based approach.
At 0.5mg (recommended)
Common (2–5% of users)
Rare at 0.5mg
At 5–10mg (common OTC dose)
More common
Chronic high-dose use concerns
Who Should Consult a Doctor Before Using Melatonin
Insufficient human safety data for melatonin in pregnancy. Animal studies suggest possible effects on fetal reproductive development. Avoid unless specifically directed by your obstetrician or GP.
Consult a GP or paediatrician before use in children or adolescents. Children produce significantly higher natural melatonin levels than adults; supplementation without clinical indication is not recommended. Age-appropriate dosing is well below adult doses. Short-term use under medical supervision may be appropriate for specific conditions (DSPD in adolescents, autism-related sleep difficulties) but requires professional guidance.
Melatonin stimulates immune system activity. In autoimmune conditions (rheumatoid arthritis, lupus, MS, inflammatory bowel disease), this may worsen disease activity or symptoms. Discuss with your specialist before any use.
Clinically significant interactions with: warfarin and anticoagulants (increased bleeding risk); anticonvulsants (carbamazepine, phenytoin — altered seizure threshold); diabetes medications (glucose regulation effects); immunosuppressants (cyclosporin interaction); nifedipine (blood pressure effect); and CNS depressants and benzodiazepines (additive sedation). Show your full medication list to a pharmacist before starting melatonin.
Sleep Cycle Timing
Pair Melatonin Timing with Cycle-Aligned Wake Times
Melatonin helps with circadian phase alignment. The sleep cycle calculator ensures your alarm lands at the end of a 90-minute cycle in N1 sleep — minimising grogginess regardless of melatonin use.
Open Sleep Cycle CalculatorFrequently Asked Questions
Does melatonin help you fall asleep?
Melatonin can help with sleep onset in specific situations — particularly when the cause of delayed sleep onset is circadian timing misalignment. If you consistently struggle to fall asleep before midnight to 2am (delayed sleep phase), melatonin taken 5–6 hours before your current natural sleep onset may gradually advance your clock over 2–4 weeks of consistent use. For jet lag, 0.5mg at the destination bedtime is supported by the Herxheimer and Petrie (2002) Cochrane systematic review as moderately effective. However, for general sleep onset difficulty without a circadian component — where you find it hard to fall asleep despite appropriate timing but no phase problem — melatonin has weaker evidence. CBT-I has substantially stronger research support and is the AASM first-line recommendation for chronic insomnia.
How much melatonin should I take for sleep?
Research supports 0.5mg as the optimal general dose. Zhdanova et al. (2001) showed 0.3mg produces the same sleep onset reduction as 3mg in a randomised controlled trial at MIT. Brzezinski et al. (2005) confirmed 0.5mg is as effective as 5mg for circadian phase shifting, with fewer side effects. If your pharmacy only stocks higher doses, cutting a 3mg tablet into sixths or a 1mg tablet in half provides the evidence-based range. Taking more than 0.5–1mg does not improve sleep onset further and increases the risk of morning grogginess, vivid dreams, and possible suppression of your body’s natural melatonin production over time. If you are currently taking 5–10mg and experiencing next-day drowsiness, the dose is very likely the primary cause. Consult a pharmacist about dosing, particularly if you take prescription medications.
When should I take melatonin for sleep?
The correct timing depends on your goal. For sleep onset support: take 0.5mg 30–60 minutes before your desired bedtime. For circadian phase advance (shifting sleep earlier): take 0.5mg 5–6 hours before your current natural sleep onset — not at bedtime. Taking melatonin at bedtime for phase advance is the single most common timing mistake; the clock-shifting signal needs to arrive well before your DLMO. For jet lag: take 0.5mg at the destination’s intended bedtime from night 1 of arrival, continuing for 3–5 nights. For shift work: take 0.5mg at the beginning of your intended sleep period. The timing calculator above calculates the specific recommended time for each use case.
Why does melatonin make me feel groggy the next morning?
Morning grogginess after melatonin is almost always a dose problem, not a product problem. At 5–10mg — the most common OTC dose — melatonin receptor occupancy extends well into the following morning, producing a prolonged sedative-adjacent effect that you experience as grogginess. At the physiologically correct dose of 0.3–0.5mg, this effect is minimal because receptor occupancy clears during the night. The solution in most cases is to reduce to 0.5mg rather than switching brands or stopping entirely. If grogginess persists at 0.5mg, try taking it 30 minutes earlier in the evening so the receptor occupancy window shifts further from your wake time.