A 1 mg dose of immediate-release melatonin lasts roughly four to five hours in your body. Its half-life is about 45 minutes, meaning half the dose is cleared in under an hour, and most of it is gone well before morning. That short window is actually by design: your body’s own melatonin follows a similar rise-and-fall pattern to help you fall asleep without lingering into the next day.
How Quickly It Kicks In and Peaks
After swallowing a 1 mg immediate-release tablet, melatonin is absorbed quickly and typically reaches its highest concentration in your blood within 30 to 50 minutes. This is why most sleep experts suggest taking it 30 minutes to an hour before you want to fall asleep. The sleepiness you feel is strongest around this peak, then gradually fades as your liver breaks the hormone down.
The 45-Minute Half-Life, Explained
Melatonin’s plasma half-life is approximately 45 minutes in healthy adults, with a normal range of 30 to 60 minutes. “Half-life” means the time it takes for the amount in your bloodstream to drop by half. So if you take 1 mg at 10 p.m., roughly 0.5 mg remains active around 10:45, about 0.25 mg by 11:30, and so on. After four or five half-life cycles, the amount left is negligible.
One important detail: melatonin follows linear kinetics across doses from 1 mg up to at least 6 mg. The half-life stays the same regardless of dose. A 5 mg tablet doesn’t last dramatically longer; it just starts at a higher concentration and takes a couple of extra half-life cycles to reach zero. In a study of healthy men who took 10 mg (ten times a typical low dose), blood levels still dropped to zero within about five hours.
Immediate-Release vs. Extended-Release
The four-to-five-hour window applies specifically to immediate-release melatonin, which is the most common type sold as a supplement. Extended-release (sometimes labeled “slow release” or “prolonged release”) formulations work differently. They use a coating or matrix that dissolves gradually, releasing melatonin into your system over a longer stretch.
In a crossover study comparing the two formats, extended-release melatonin stayed above sleep-maintaining levels for a median of 6.7 hours, compared to 3.7 hours for immediate-release. That distinction matters depending on your sleep problem. If you have trouble falling asleep but stay asleep fine, immediate-release at 1 mg is a good match. If you wake up in the middle of the night, extended-release may cover more of the night.
What Speeds Up or Slows Down Clearance
Your liver does the heavy lifting when it comes to breaking down melatonin. More than 90% of it is processed by a specific liver enzyme called CYP1A2. Anything that affects this enzyme changes how long melatonin sticks around in your system.
Smoking is the biggest accelerator. Smokers clear melatonin about 1.8 times faster than nonsmokers because tobacco smoke ramps up CYP1A2 activity to roughly 1.6 times normal levels. If you smoke and take 1 mg of melatonin, it may wear off noticeably sooner than the typical four-to-five-hour window.
On the flip side, certain medications can slow CYP1A2 down. Some antidepressants, certain antibiotics, and even large amounts of caffeine compete for the same enzyme, potentially causing melatonin to linger longer than expected. If you’re taking other medications and notice unusual next-day grogginess from a low dose, enzyme competition could be the reason.
How Age Changes the Picture
Your body’s natural melatonin production declines as you get older. Older adults produce less of it, and their circadian rhythm becomes weaker and less sharply defined. This means a supplemental dose of 1 mg represents a larger relative boost for an older person than for a younger one.
Liver function also tends to slow with age, which can modestly extend how long supplemental melatonin stays active. Younger adults typically have robust, high-amplitude melatonin cycles that rise and fall sharply. In older adults, these rhythms flatten and sometimes shift earlier in the evening. A 1 mg dose may feel more potent and last a bit longer in someone over 65 compared to a 30-year-old, simply because the body clears it more slowly and has less of its own melatonin to compete with.
Practical Timing for 1 mg
For most people, 1 mg of immediate-release melatonin provides a meaningful sleep signal for roughly three to four hours after it peaks, with trace amounts fading out by the five-hour mark. That makes it well-suited for helping you fall asleep without causing morning drowsiness, which is one of its advantages over higher doses.
Take it about 30 to 60 minutes before your target bedtime on an empty or light stomach. Fatty meals can delay absorption and push the peak later. If you find that 1 mg helps you fall asleep but you’re waking at 2 or 3 a.m., the dose isn’t necessarily too low. It may simply be wearing off as expected, and switching to an extended-release format could provide more continuous coverage through the night.