Sleep Doctor independently selects the products we test. We may earn a commission if you buy through the links on our site.

How Long Does Melatonin Last?


Written by Afy Okoye

Reviewed by Dr. Michael Breus

Our Editorial Process

Table of Contents

About 2% of U.S. adults take the dietary supplement melatonin, which is often used to promote sleep in people who have jet lag, do shift work, or have short-term sleep problems. More than five times as many U.S. adults use melatonin compared to twenty years ago. 

We cover how melatonin works, how long its effects last, and best practices for taking the supplement.

How Does Melatonin Work?

Melatonin helps regulate when you feel tired and when you feel awake. The human body naturally produces the hormone melatonin when the eyes are exposed to darkness, which then prompts tiredness. Conversely, being exposed to light blocks the release of melatonin, prompting alertness.

In addition to being made by the body, melatonin can also be made in a lab or derived from animals. These types of melatonin are sold as dietary supplements in the U.S. and as prescription drugs in the Europe Union. Melatonin supplements are usually taken by mouth on a short-term basis. 

Taking melatonin short-term appears to be safe for both adults and children, but talk with your doctor before beginning it or any supplement.

Duration of Melatonin’s Effects in the Body

Melatonin stays active in the body for an estimated four to five hours. The body absorbs it quickly and peak levels are reached within 50 minutes on average. Then, the amount present in the blood is reduced by half every 20 to 50 minutes. However, the dosage of melatonin taken can impact how quickly it’s absorbed and how long it remains in the body.

Some melatonin supplements may begin working more quickly or more slowly than average, depending on their formulation. Both fast-acting and slow-release formulas are available. These different formulas can be more useful for certain people depending on how quickly they want to become tired and how long they’d like to remain asleep.

Factors Affecting Melatonin’s Duration

Multiple factors can impact how long melatonin remains active in the body.

  • Age: In older adults, melatonin may remain active in the body for longer periods of time than it does in younger adults. As a result, they may feel tired the next day after having taken melatonin.
  • Medication use: Multiple types of medication may affect melatonin’s impact. For example, oral hormonal birth control increases melatonin levels generally, and may increase it even more when taken with melatonin supplements. Similarly, taking both sedatives and melatonin can make a person excessively sleepy.
  • Supplement use: The herbal supplement vitex agnus-castus increases melatonin levels, and taking it and melatonin together may lead to increased side effects.
  • Caffeine use: Ingesting caffeine and melatonin at the same time has been found to greatly increase melatonin levels in the body. 
  • Smoking status: Research has found that smoking cigarettes dulls the impact of melatonin supplements, by reducing its peak levels and increasing how quickly it’s cleared from the body in comparison to non-smokers.

Best Practices for Taking Melatonin

There are a few things to keep in mind before taking melatonin supplements.

Talk With Your Doctor First

Since melatonin supplements aren’t a good treatment for everyone, you should talk with your doctor before you begin taking them. Be sure to mention any illnesses you have, along with prescription drugs and dietary supplements you take, to ensure there won’t be an interaction.

Start With a Low Dose

Experts recommend people take 1 to 5 mg of melatonin for insomnia and 1 to 3 mg for daytime sleep related to shift work. Doses over 5 mg may not be safe, and melatonin supplements may contain more melatonin than their labels state. For this reason, it’s best to start with a low dose and increase if needed.

Don’t Operate Machinery

Since melatonin can make you fall asleep, you should avoid driving or operating machinery for up to five hours after taking it.

Keep Away From Children

If you’re an adult taking melatonin supplements, be sure to keep them where children and teenagers cannot easily access them. People in these age groups may be more likely to experience a melatonin overdose. Do not give melatonin to children without discussing it with their doctor first.

About The Author

Afy Okoye

Staff Writer, Sleep Health

Afy is a writer and creative strategist in San Francisco with a master’s degree in international health policy from the London School of Economics. She has written for VeryWell Health,, and Paste magazine and edited peer-reviewed journal manuscripts for Elsevier. Afy says her work with The Sleep Doctor is anything but “sleepy.” She enjoys the opportunity to learn new information and share knowledge that gives people the power to make better choices. Afy also likes to read non-fiction, do creative writing, and travel solo.

  • POSITION: Side Sleeper
  • TEMPERATURE: Hot Sleeper

Ask the Sleep Doctor

Have questions about sleep? Submit them here! We use your questions to help us decide topics for articles, videos, and newsletters. We try to answer as many questions as possible. You can also send us an emailPlease note, we cannot provide specific medical advice, and always recommend you contact your doctor for any medical matters.