When to take it

How long does melatonin last?

By GyroscopeUpdated November 14, 20266 sources

Half of a regular tablet is gone about an hour after its peak, and the peak comes about 40 minutes after you swallow it, so 0.5 mg at 10:30pm is back to a normal night’s level by about midnight. A 10 mg tablet starts about 33 times higher, so it stays above your own melatonin until somewhere between 3:45 and 6:45am.

People ask how long melatonin lasts as if every tablet lasts the same. Any dose clears at about the same rate, but a bigger dose starts much higher, so it takes many more halvings to come back down. The number on the bottle decides whether it’s gone by your alarm.

We’d pick a dose that’s gone long before you get up. If you wake up groggy, cut the dose before you change anything else.

Picture a bath that drains half its water every hour. Fill it to the brim and there’s still water in it at breakfast. Put in an inch and it’s empty before you’re asleep.

Your dose, hour by hour

Every dose in the table is taken at 10:30pm and peaks at about 11:10pm. Each range runs from the measured half-life of about 54 minutes to a slower 1.5 hours, which we use for people who clear it slowly.

Where those numbers come from

The height comes from a 1994 study at MIT. Researchers gave 20 men doses from 0.1 to 10 mg, and the amount in their blood rose in step with the dose. The 0.1 and 0.3 mg doses gave peaks inside the normal range of a person’s own night levels. In 2001 the same group found that 0.3 mg brought older adults’ night levels back to normal, while 3 mg kept melatonin raised into the daylight hours.

The speed comes from a 2016 study in Copenhagen. 12 healthy men swallowed 10 mg, peaked at 40.8 minutes on average, and then lost half of it every 53.7 minutes.

People don’t all clear it at the same speed. In surgery patients given 10 mg, the half-life was about 60 minutes before an operation and about 104 minutes the evening after it. The US National Center for Complementary and Integrative Health says melatonin may stay active longer in older people and cause daytime drowsiness, so if you’re 60 or over, use the slow end of each range.

What about slow-release?

Slow-release tablets are built to keep the level up through the night, so the table doesn’t apply to them. In a 1995 trial in older adults with insomnia, 2 mg slow-release helped them stay asleep, while the same dose as a regular tablet helped them fall asleep. The label sets when to take one.

What’s left in the morning

Your own melatonin falls toward morning, so a dose that’s still above your own night’s peak near your alarm is the one that leaves you foggy. A 3 mg tablet taken at 11pm is back under by somewhere between 2:40 and 4:40am. A 10 mg tablet taken at 11pm can stay above it until 4:15 to 7:15am, which is why people wake up groggy.

Put your own dose, form and alarm into the tool below to see the curve across your night, or go deeper in the night curve. Don’t drive after a dose.