How long does melatonin last?

We all have a restless night occasionally. Melatonin is a common sleep aid to help you stop tossing and turning and get a good night’s sleep. But what is this supplement, and how long does melatonin last in your body?

Melatonin is a hormone that your body naturally makes at night to promote sleep quality. If you’re having sleep problems, melatonin supplements are available over the counter in the U.S. to help you get some better sleep.

Before you take melatonin, you should know the potential impacts it can have on your health. Keep reading to learn everything you need to know about how your body uses melatonin to help you sleep.

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Your circadian rhythm regulates many of the processes in your body necessary for good overall health, including when you feel sleepy. This is a natural cycle that averages around 24 hours. One of the main ways this sleep-wake cycle is regulated is through the presence of light and dark, which stimulate the release of the hormone melatonin (Basit, 2021).

Here’s how this works: Your body converts the amino acid tryptophan into the neurotransmitter serotonin. Some of that serotonin makes its way to the pineal gland in the brain. When your brain senses it's getting dark, the serotonin in the pineal gland is converted into melatonin, and you begin to feel sleepy (Savage, 2021).

Your body usually makes all of the melatonin that it needs. However, some conditions can cause less melatonin production in your brain, leading to sleep issues. Fortunately, melatonin pills are also available as a dietary supplement.

Melatonin has been most frequently studied and recommended by healthcare providers for treating the following conditions (Savage, 2021):

• Primary insomnia (insomnia not due to some secondary cause, like a medication or health condition)

• Age-related insomnia

• Jet lag disorder

• Non-24 disorder and other circadian rhythm disorders

• Shift work sleep disorder

• Post-traumatic brain injury

• Neurological disorders

Although there are no formal treatment recommendations yet, researchers are currently looking at the way melatonin works in treating other conditions such as (Savage, 2021):

• Cancer

• Metabolic disorders

• Cardiovascular disorders

• Gastrointestinal (GI) conditions

• Mental disorders

• Pain syndromes

• Reproductive problems

The amount of time that it takes melatonin to work depends on the form you take it in. Melatonin is available as (Savage, 2021):

• Immediate-release oral form

• Extended-release oral form

• Combination of immediate and extended slow-release oral form

• Intravenous form (used in research studies)

After intravenous (IV) administration, melatonin is rapidly (within minutes) distributed throughout the body and then eliminated. If you take it orally, melatonin levels will peak in your bloodstream after about an hour (Tordjman, 2017).

Whether you take it by IV or by mouth, your body quickly processes the melatonin you’ve taken. It does this mainly through your liver but also through your kidneys (Tordjman, 2017).

The amount of time it takes melatonin to leave your system depends on the type of formulation you take (for example, immediate release or controlled release). A typical dose of oral, immediate-release melatonin will clear from your body faster than a controlled or extended-release formulation.

A usual dose of immediate-release melatonin (1–5 mg) will cause your blood concentrations of melatonin to peak within an hour after taking it. Your body will return to baseline levels within four to eight hours (Tordjman, 2017).

Natural melatonin release is enhanced by darkness and inhibited by light. The retinas in your eyes tell a particular gland in your brain—called the pineal gland—about the brightness of your surroundings. The pineal gland will release melatonin shortly after sundown and continue until the middle of the night (between 2 am and 4 am). It then begins to decrease during the second half of the night (Tordjman, 2017).

Nearly 80% of your body’s melatonin is made at night. The concentration in your blood is very low during the day (Tordjman, 2017).

There are no official dosing guidelines for melatonin. However, the doses used in most research studies varied from 0.1 mg to 10 mg, taken up to two hours before bedtime (Savage, 2021).

Your body’s response to melatonin supplements is complex, but the simple version is that it helps to regulate your circadian rhythm and sleep schedule. Melatonin has been shown to provide a modest improvement in sleeplessness (Momin, 2021).

There are a large number of both animal and human studies that document that the short-term use of melatonin is safe for adults, even in large doses. No studies have shown that melatonin poses any serious risk of side effects. However, minor side effects, such as headache, rash, stomach upset, and nightmares, have been reported (Savage, 2021). Even with long-term administration, only mild adverse effects were reported (Andersen, 2016). 

Be aware that there is a lack of safety information for using melatonin in pregnant or breastfeeding people, so its use is not recommended in these populations. Also, the long-term safety of using melatonin in children and adolescents still needs more investigation (Andersen, 2016).

Multiple studies have shown evidence to suggest that people can develop a tolerance to melatonin over time. However, it is considered non-habit forming, meaning that taking it shouldn’t lead to a melatonin addiction (Savage, 2021).

One possible adverse effect to taking melatonin long-term is that some preliminary observations have suggested that taking melatonin for an extended period might lower the quality of semen in healthy males. More study is needed before this can be confirmed, though (Savage, 2021).

The U.S. Food and Drug Administration (FDA) doesn’t regulate supplements. This is the reason that there are no formal dosing guidelines for melatonin (Savage, 2021).

However, this can also pose a problem because the actual concentration of melatonin in the supplement can vary. This further makes accurate dosing a challenge and might be responsible for some variations in clinical trial results (Savage, 2021).

Studies have found significant variations in the amount of melatonin present in the tablets. An analysis of 31 melatonin supplements found that the melatonin content was more than 10% above or below the labeled amount in more than 71% of the products tested. You can help protect yourself from getting more or less melatonin than you need by buying from a reputable brand (Erland, 2017).

To ensure the brand you’re buying is high quality, look for supplements with approval from the United States Pharmacopeia, an independent non-profit organization. Searching for supplements marked “USP verified” can help ensure the quality and dosing of supplements (Savage, 2021).

Side effects of melatonin

Melatonin is considered a relatively safe supplement to help you sleep better, although there are some possible side effects, particularly with higher doses. Common side effects of melatonin include (Savage, 2021):

• Drowsiness the next day

• Changes in blood pressure causing dizziness

• Headaches

• Nausea

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How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

November 04, 2021

Written by

Ellyn Vohnoutka, BSN, RN

Fact checked by

Steve Silvestro, MD

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About the medical reviewer

Steve Silvestro, MD, Ro

Dr. Steve Silvestro is a board-certified pediatrician and Associate Director, Clinical Content & Education at Ro.