The guide

Melatonin timing: why the hour changes the direction

By GyroscopeUpdated November 14, 202610 sources

The same tablet does opposite things at different hours. Taken in the few hours before your own melatonin starts, it moves your body clock earlier. Taken just after you wake, it moves it later. Around the time you fall asleep it barely moves the clock at all, and in a lab 0.5 mg at its best hour moved the clock as far as 3 mg at its best hour.

That’s why the first question to ask is what you want melatonin to do. The answer sets the hour, and the dose comes after.

Why does the bottle say bedtime?

Because that’s how melatonin got used. The 2024 review of 26 trials named the schedule most used in clinics as 2 mg, 30 minutes before the bedtime you want. Bottles say to take it before bed, and most advice online says 30 to 60 minutes.

The trouble is that by 30 minutes before bed, your own melatonin has usually been up for a couple of hours. A tablet then adds a little more of a signal that’s already on. The hours earlier in the evening are the ones where a tablet can still say something new.

A simple way to picture it

Think of pushing a child on a swing. Push as the swing moves away from you and it speeds up. Push against it as it comes back toward you and it slows down. Push at the very top and not much happens.

Your body clock is the swing and a tablet is the push. In the afternoon it speeds the clock up, so your night comes earlier. Just after waking it slows the clock down. Around bedtime it barely moves it.

How can one pill move your clock both ways?

Scientists map this with a phase response curve. They give the same dose at different hours and measure how far, and which way, the clock moves each time.

In 2010 Helen Burgess and her team at Rush University in Chicago did it for 0.5 mg. 34 healthy adults aged 18 to 42 came into the lab twice for 5 days. Each day they took one pill at the same clock time, melatonin in one session and a placebo in the other, without knowing which. In between, they lived in cycles of 2.5 hours awake in dim light and 1.5 hours in the dark, so daylight couldn’t move their clocks. The researchers measured when each person’s own melatonin started, before and after.

• The biggest moves earlier came in the afternoon, 2 to 4 hours before the person’s own melatonin started. The fitted curve peaked 3.3 hours before.
• Three days of 0.5 mg moved the clock up to 1.5 hours earlier on the fitted curve, and as much as 2.9 hours in some people.
• The moves later were smaller and less clear. The fitted curve peaked soon after waking.
• 0.5 mg worked best a little later in the day than 3 mg. At each dose’s own best time, the two moved the clock about the same amount.

Light has a curve too, drawn the other way round. In a 2003 study of 21 people at Brigham and Women’s Hospital and Harvard, bright light before the body’s temperature low (a few hours before you’d normally wake) moved the clock later, and light after it moved the clock earlier. The figure below puts both on one ring.

Why about 5 hours before bed?

Your own melatonin starts about 2.5 hours before your usual bedtime. The best time for 0.5 mg is 2 to 4 hours before that start, which puts it roughly 4.5 to 6.5 hours before bed. Eastman and Burgess’s working estimate for 0.5 mg is 2 hours before your melatonin starts, or 4.5 hours before sleep. For 3 mg it’s 5 hours before your start, or 7.5 hours before sleep.

The window tool uses the middle of that range, 0.5 mg between 4 and 2 hours before your start, with 3 hours before as the one time to remember.

When your own melatonin starts explains where the start times come from.

Does it work outside a lab?

Yes, more slowly. In 2018 a team at Monash University in Australia ran a trial in 116 people with delayed sleep phase, the body clock problem where you can’t fall asleep until very late. Their average age was 29. For 4 weeks they took 0.5 mg or a placebo 1 hour before the bedtime they wanted, at least 5 nights a week, and everyone was given a fixed bedtime.

On melatonin, sleep came 34 minutes earlier than on placebo, somewhere between 8 and 60 minutes allowing for chance. Clinicians rated 52.8 percent of the melatonin group as more than minimally improved, against 24.0 percent on placebo.

One hour before bed sounds like the old bedtime advice, but these people were picked because their own melatonin started after the bedtime they wanted, or within 30 minutes before it. For them, an hour before bed was still before their own melatonin started. The authors credited most of the gain to melatonin’s sleep-promoting effect working together with the fixed bedtime.

The lab moved clocks 1.5 hours in 3 days of dim light. The trial moved sleep 34 minutes in 4 weeks of ordinary life, with ordinary evening light. The American Academy of Sleep Medicine’s 2015 guideline came out in favor of timed melatonin for delayed sleep phase, as a weak recommendation.

What about falling asleep faster tonight?

Earlier still beats bedtime. The 2024 review of 26 trials found that the more time people left between the dose and sleep, the more it shortened the time to fall asleep. The authors suggested about 3 hours before the bedtime you want, against the usual 30 minutes.

An older MIT study pointed the same way. Volunteers took 0.3 or 1 mg at 6, 8 or 9pm, and every combination shortened the time to fall asleep, with no grogginess on morning tests.

How fast can you move your bedtime?

No trial has tested a pace for the public. We suggest moving bedtime and the dose 15 to 30 minutes earlier every 2 to 3 days, once your sleep has followed. At that pace a 2.5 hour move takes about 10 days to a month.

Here’s how that looks for Tom, 27, who wakes at 10:30am on free days, usually falls asleep around 2am, and wants to be asleep by 11:30pm. His melatonin probably starts around 11:35pm. His window is 0.5 mg between 7:35 and 9:35pm, with 8:35pm as the one time to remember. He keeps one wake time, gets outside soon after it, and switches to lamps once he’s taken it.

And moving later?

There’s no pill window for that. Melatonin’s delay zone is just after you wake up, which is the hour it makes you drowsy. The 2002 Cochrane review of jet lag trials warned that taken early in the day, it can cause sleepiness and slow your adjustment. Light does the job better. Bright light in the evening and a later wake time move your clock later.

An afternoon dose can make you drowsy too. In the MIT noon study, every dose from 0.1 mg up made people sleepier and slower on a listening test. Don’t drive after a dose, whatever the hour.

Won’t a 5pm dose put me to sleep at work?