Melatonin - when it helps and when it does not

Melatonin is sold as a sleep aid. It is one. But it is most effective for problems that are not what most people call "insomnia". Understanding when melatonin will actually help and when it will not changes how to use it and whether it is worth the cost.

What melatonin actually is

Melatonin is a hormone secreted by the pineal gland in the brain. Secretion begins in the evening as ambient light falls, rises to a peak in the middle of the night, and falls toward morning. It signals the body's circadian clock about when to be asleep, but it does not directly induce sleep itself.

This distinction matters. Melatonin shifts the timing of sleep readiness; it does not strongly act as a sedative. Taking it when your body's natural melatonin is already high (middle of the night) does almost nothing. Taking it several hours before your natural rise can advance your circadian phase and make falling asleep earlier possible.

UK regulatory status

In the UK, melatonin is a prescription-only medicine in most formulations and doses. Circadin (prolonged-release melatonin 2mg) is the standard UK-licensed preparation, licensed for insomnia in adults over 55. Immediate-release melatonin is prescribed off-label for other uses.

Over-the-counter melatonin sold in the US and online at 5 to 10mg doses is not legally available from UK pharmacies. Patients occasionally buy it from abroad; the doses are supraphysiological and often produce morning hangover or next-day fatigue.

When melatonin clearly works

Jet lag. Small dose (0.5 to 3mg) of immediate-release melatonin taken at the new local bedtime, for 3 to 5 nights, reliably accelerates circadian adaptation to a new time zone. Most effective for eastward travel (which requires phase advance, the harder direction). Useful for frequent international travellers and for structured preparation for trips.

Delayed sleep phase disorder. Small dose (0.3 to 1mg, much smaller than commercial over-the-counter products) taken 4 to 6 hours before the current habitual sleep time, combined with morning bright light, reliably advances the circadian phase over weeks. This is the single most effective medical intervention for delayed sleep phase.

Shift work. Timed melatonin can help consolidate sleep after night shifts when the patient is trying to sleep during the day. Evidence is less strong than for jet lag but useful in practice.

Insomnia in older adults. Circadin (2mg prolonged-release) has modest benefit in older adults with primary insomnia, particularly those with reduced endogenous melatonin secretion that comes with age. Effect size is smaller than Z-drugs but durable over months without tolerance.

Paediatric neurodevelopmental sleep problems. Paediatric specialists use melatonin for specific indications in children with autism or ADHD who have severe sleep-onset problems. Out of scope for our adult service but worth flagging as a legitimate use.

When melatonin is often tried but usually does not help

Chronic primary insomnia in working-age adults. Most patients with long-standing insomnia have already tried melatonin before seeing us. The response is usually disappointing. Insomnia is a hyperarousal problem; melatonin shifts timing, not arousal. Effective treatment is CBT-I, not melatonin.

Occasional sleep onset difficulty in healthy sleepers. For a one-off bad night, melatonin is unlikely to help. It is a circadian signal, not a sedative.

Middle-of-night awakenings. Not a melatonin-responsive pattern. The issue is usually insomnia, apnoea, or specific medical conditions (nocturia, reflux).

Chronic severe insomnia responsive to Z-drugs. If a patient is clearly helped by Z-drugs but nothing else, melatonin is unlikely to be an equivalent substitute. Managing the Z-drug dependence and working on the underlying sleep problem is the better path.

Dose matters - and usually lower is better

The single biggest error with melatonin is taking too much. Physiological doses (0.3 to 1mg immediate release, or 2mg prolonged release) are more effective for circadian shifting than supraphysiological doses (3 to 10mg).

Higher doses may feel more sedating but usually reflect direct sedative effects from pharmacological excess, not circadian action. They also carry more next-day hangover (morning fatigue, headache).

When we prescribe, we start low. We raise the dose only if genuinely needed and if low-dose response is clearly inadequate.

Timing matters

For circadian advance (delayed sleep phase), melatonin is taken 4 to 6 hours before current bedtime. Not at bedtime. The phase-shifting window is well before sleep onset.

For sleep consolidation in older adults (Circadin), the dose is taken 1 to 2 hours before target bedtime.

For jet lag, the dose is taken at new local bedtime.

Getting the timing wrong produces either no effect or, at worst, shifts the clock in the wrong direction.

Safety and side effects

Melatonin is well tolerated in most adults. Common mild side effects: morning grogginess (usually means dose too high), headache, vivid dreams, rarely mood changes or irritability.

Drug interactions to be aware of: fluvoxamine (raises melatonin levels markedly), warfarin (modest interaction), some immunosuppressants, some antihypertensives. We review medication list before prescribing.

No evidence of dependence or tolerance with long-term use at physiological doses. No withdrawal on stopping.

Safety in pregnancy and breastfeeding is not well-established; we do not routinely prescribe in these groups.

What we prescribe and how

For delayed sleep phase: immediate-release melatonin 0.3 to 1mg, 4 to 6 hours before target bedtime, combined with morning bright light, for 4 to 6 weeks.

For jet lag: immediate-release melatonin 1 to 3mg at new local bedtime for 3 to 5 nights.

For older adult insomnia: Circadin 2mg (prolonged release) 1 to 2 hours before bedtime.

For shift work: individualised; usually 1 to 3mg immediate-release at target sleep time.

We do not prescribe 5mg or 10mg immediate-release as routine. We do not prescribe for occasional mild sleep onset difficulty in otherwise healthy sleepers.

Combining melatonin with other treatment

For delayed sleep phase, melatonin plus morning bright light plus gradual schedule shift is the effective combination. Melatonin alone is less effective.

For insomnia plus circadian component (common in younger adults), CBT-I plus timed melatonin is often the right plan.

For jet lag, melatonin plus managed light exposure on arrival at the new destination accelerates adaptation further.

The honest bottom line

Melatonin is a useful tool for circadian problems and for older-adult insomnia, less useful for working-age insomnia where CBT-I is more effective. Dose low, time correctly, and match the use to the problem. Taking 5mg at bedtime every night for general insomnia is usually ineffective.

Ready to start?

If this article has made you think our assessment might help, the next step is a short consultation with one of our sleep-medicine doctors.

Begin your consultation at this link. Online with a WatchPAT One home study, or in person at Westfield London.