Melatonin: how does it work, and when does it really help?

Melatonin may well be the most misunderstood substance in the sleep world. It is sold and used as if it were a natural sleeping pill — a little pill that "switches you off." But melatonin works very differently from a sleeping pill. It is not a sedative, but a timing hormone: it tells your body what time it is biologically. That difference determines exactly when melatonin does help and when it does not. This article explains how it works, who it is useful for, and what to watch out for.

How does melatonin actually work?

Your body produces melatonin itself in the pineal gland, following a fixed rhythm: the level begins to rise a few hours before your normal bedtime, peaks in the middle of the night, and falls toward morning. Melatonin is thereby the chemical "night signal" of your biological clock. It makes you sleepy not so much by numbing your brain, but by letting your whole system know: it is now night.

Daylight, and especially morning light, actually suppresses production. That is why Thuisarts.nl recommends getting enough outdoor light during the day — that reinforces your natural rhythm more than a pill in the evening ^[1]. When you take melatonin as a supplement, you add an extra timing signal. The effect therefore depends heavily on the timing of when you take it: the same pill can advance your clock, delay it, or do almost nothing, depending on where you are in your own rhythm.

When does it actually help?

Melatonin is at its best when your biological clock is out of sync with the time you want to sleep.

• Jet lag. After a flight across several time zones, your internal clock lags behind or runs ahead of the local time. A Cochrane review of randomized studies concludes that melatonin, taken at the right time, can reduce jet lag remarkably well after travel across several time zones ^[4]. Thuisarts.nl also mentions melatonin specifically in the context of long-distance travel, and much less for ordinary sleep problems ^[7].
• Delayed sleep phase. People — often young people — who fall asleep only very late and do not wake up on time in the morning have a clock shifted backward. A meta-analysis shows that a low dose of melatonin, taken a few hours before the (late) natural sleep-onset time, can move the clock forward so that falling asleep earlier becomes possible ^[5].
• Some children and older adults. For certain children (for example with a developmental disorder) or for older adults with a demonstrably disturbed rhythm, a doctor may prescribe melatonin. That is tailored care — not general advice.

The common thread: melatonin helps when something is wrong with the timing of your sleep, not when you "just" sleep badly.

When does it not help?

For classic, chronic insomnia — you lie awake a long time, wake up at night, worry — melatonin is disappointing. Its effect on sleep-onset time is small and inconsistent in research. The clinical guideline of the American Academy of Sleep Medicine (AASM) from 2017 even advises clinicians not to use melatonin for falling or staying asleep in insomnia, because the evidence for efficacy falls short ^[3].

Dosing and timing: less is often better

With melatonin, "more is better" does not apply. To shift your body clock, a low dose (often on the order of 0.5 up to a few milligrams) at the right time works better than a high dose just before bed. Too high a dose, or a dose at the wrong moment, can even counteract the desired shift. The timing is more important than the amount: taking it a few hours before your natural sleep-onset moment usually gives the best forward shift. Because this is precise — and varies from person to person — it is wise to discuss dose and timing with your GP or pharmacist.

Safety and the regulation problem

Short-term use of melatonin usually causes few side effects in adults; sometimes drowsiness, headache, or dizziness. Less is known about long-term use, and particularly about use in children, so caution is warranted.

A separate point of attention is that over-the-counter melatonin in the Netherlands is sold as a dietary supplement and therefore does not have the same strict quality control as a registered medicine.

In short, melatonin is a useful substance — but a precision instrument, not a general sleep aid. Use it in a targeted way for jet lag or a shifted rhythm, choose a low dose at the right moment, and for persistent insomnia take it to your GP rather than continuing on your own.