Melatonin: what it actually does, what dose makes sense, and who it helps

Melatonin is sold as a sleeping pill, and it isn't one. It's the hormone your brain uses to tell the rest of your body that it's dark — a timing signal, not an off switch. That difference explains why it works for one person by the third night and does nothing for another after a month.

What melatonin actually does

Your pineal gland starts releasing melatonin roughly 2 hours before your usual sleep time, and across a whole night your body produces somewhere around 0.1 to 0.3 mg total. Light suppresses that release: outdoors on an overcast day you get several thousand lux, while an average living room in the evening sits at 100 to 300 lux — enough to push the signal later.

Melatonin doesn't knock you out the way prescription hypnotics do. It shifts your body clock and slightly lowers the threshold for falling asleep. That's why trial results are modest and fairly consistent: falling asleep about 7 to 12 minutes faster, and 8 to 30 minutes more total sleep per night. Useful if you're short 15 minutes. Useless if you're short 2 hours.

Dose: less works better than more

This is where most people get it wrong. Shelf products are usually 3, 5 or 10 mg — 10 to 30 times what your body makes on its own. More melatonin doesn't mean a stronger signal, it means a longer one, spilling into the morning and leaving you foggy, headachy and slow until 10 or 11 a.m.

• Starting dose: 0.5 mg. In head-to-head comparisons, 0.5 mg shifts the clock as well as or better than 5 mg. If all you have is 3 mg tablets, split them — it's imprecise, but closer to the target than a whole tablet.
• Sensible ceiling: 1 to 3 mg. Above that you don't get more effect, only more side effects.
• Trial period: 10 to 14 days. If two weeks bring no clear difference, stop. Escalating to 10 mg is not the fix.

Timing matters more than dose

With melatonin, the clock on the wall decides more than the number of milligrams on the box.

• You fall asleep at 2 or 3 a.m. but have to be up at 7: 0.5 mg taken 4 to 6 hours before your current spontaneous sleep onset, plus 20 to 30 minutes of bright light right after waking. Move bedtime earlier by 15 minutes every 2 to 3 days, not by 2 hours at once.
• You go to bed on schedule but need 45 minutes to drop off: 0.5 to 1 mg, 30 to 60 minutes before bed.
• Eastward travel, say 7 to 8 time zones: 0.5 to 3 mg at your target local bedtime for the first 3 to 5 nights. Westward flights benefit much less.
• You wake at 3 a.m. and can't get back down: melatonin generally does nothing here. That's a different problem.

Does it make sense if you train

For strength, hypertrophy and endurance there's no convincing evidence for melatonin. It doesn't meaningfully increase deep sleep and it isn't recovery in a capsule. What is well established is that a few nights under 6 hours drops your strength, distorts how hard effort feels, and raises injury risk.

Melatonin can buy you 15 minutes. It can't hand back the 90 minutes you spent yourself.

So look at what's actually wrecking your sleep first. Caffeine has a half-life of 5 to 6 hours, so 300 mg of pre-workout at 7 p.m. still leaves roughly 150 mg circulating around midnight. A heavy squat set at 9:30 p.m. raises heart rate and core temperature, and your body needs that temperature to drop to fall asleep — finish your last hard set at least 90 minutes before bed. And two or three drinks in the evening will cut REM sleep no matter what you took with them.

Fix these before reaching for a pill

1. Fixed wake time, within ±30 minutes, weekends included.
2. 20 to 30 minutes of daylight in the first hour after waking.
3. Dim the lights and drop screen brightness for the hour before bed.
4. Bedroom at 18 to 19 °C, dark and quiet.
5. Last coffee 8 to 9 hours before bed: if you're in bed at 11 p.m., nothing after 2 p.m.
6. If you're awake more than 20 minutes, get out of bed and go back only when you're sleepy.

Side effects and what we don't know

The common ones are headache, morning grogginess, vivid dreams, nausea and dizziness, and nearly all of them cluster around the 5 to 10 mg doses. Melatonin doesn't cause classic dependence and has no marked withdrawal, but data on daily use beyond 6 months is thin — especially in children and teenagers, where you're dealing with a hormone, not a vitamin.

The second issue is product quality. Supplement analyses have found actual content off the label by more than 80 percent below and several hundred percent above, with some samples containing ingredients that shouldn't be there at all. General rule: if you don't know how much you're actually taking, you can't judge whether it works.

When to see a doctor

• Trouble sleeping 3 or more nights a week for longer than 3 months — the first-line treatment there is cognitive behavioural therapy for insomnia, not a supplement.
• Loud snoring, pauses in breathing, morning headaches, or daytime sleepiness despite 8 hours in bed.
• Crawling discomfort and an urge to move your legs as soon as you lie down.
• Fatigue that persists despite decent sleep — worth checking thyroid, iron and blood count.
• If you take anticoagulants, anti-epileptics, immunosuppressants, blood pressure or diabetes medication, or if you're pregnant or breastfeeding.
• For children and teenagers — never on your own.

The short version

• Melatonin is a timing signal, not a sedative; the realistic gain is 7 to 12 minutes faster sleep onset.
• Start at 0.5 mg and don't go past 1 to 3 mg; 5 and 10 mg mostly buy you morning grogginess.
• Timing decides the outcome: 30 to 60 minutes before bed for ordinary sleep onset, 4 to 6 hours earlier if you're shifting your clock.
• It works best for eastward jet lag and a delayed sleep schedule, and poorly for 3 a.m. wake-ups.
• Give it 10 to 14 days; if nothing changes, stop and fix light, caffeine and training time instead.