Melatonin Side Effects You Should Know About

Melatonin is the most widely used sleep supplement in the world. It is sold in doses of 3mg, 5mg, and 10mg in most pharmacies, and most people assume bigger doses mean better sleep. The research tells a different story. Those doses are far higher than what your body actually produces, higher than what studies show is effective, and high enough to cause side effects that make sleep worse over time.

What Melatonin Actually Does

Melatonin is a hormone produced by the pineal gland in response to darkness. Its job is to signal to your body that it is nighttime, helping to synchronize your circadian rhythm. It does not sedate you. It does not put you to sleep the way a sleeping pill does. It tells your body what time it is.

Your brain produces somewhere between 0.1 and 0.3mg of melatonin naturally during the night. Peak blood levels are typically around 0.1 to 0.2mg. The supplements most commonly sold in pharmacies deliver 10 to 50 times this amount in a single dose.

The Side Effects of High-Dose Melatonin

Next-Day Grogginess

The most commonly reported side effect of melatonin is morning grogginess. This is particularly pronounced with higher doses. Melatonin has a half-life of 30 to 60 minutes in most people, but this varies considerably, and doses of 5mg to 10mg can leave elevated melatonin levels well into the morning hours. Elevated morning melatonin suppresses alertness and disrupts the cortisol awakening response that normally gives you energy at the start of the day.

Suppression of Natural Melatonin Production

Regular use of supraphysiological doses, doses far above what the body produces naturally, can suppress the pineal gland's own melatonin production over time. The body's hormone systems are regulated by feedback loops. When you repeatedly flood the system with exogenous melatonin, the signal to produce it internally weakens. Some research suggests this effect can persist for weeks after stopping supplementation.

Disrupted Sleep Architecture

High doses of melatonin can actually alter the structure of sleep rather than improving it. Some studies have found that doses above 1mg suppress REM sleep and increase time in lighter sleep stages, which is the opposite of what most people are looking for. The sedating effect people feel from 5mg melatonin may come partly from suppressed REM rather than from deeper, more restorative sleep.

Hormonal Effects

Melatonin interacts with several hormonal systems beyond the sleep cycle. High doses have been shown to affect reproductive hormone levels, particularly in children and adolescents. In adults, the clinical relevance of this is less clear, but it is another reason the general trend toward ever-larger doses warrants caution.

Headaches and Dizziness

Some users report headaches, dizziness, or nausea with melatonin, particularly at higher doses. These are generally mild but are more common with 5 to 10mg doses than with lower ones.

What the Research Says About Effective Doses

A meta-analysis published in PLOS ONE analyzed 19 studies on melatonin for sleep disorders and found that the effective dose range was 0.3 to 0.5mg, with diminishing returns above 1mg and no additional benefit at the doses commonly sold over the counter (Buscemi et al., 2005). Multiple independent researchers have reached the same conclusion: physiological doses are effective, supraphysiological doses are not better and carry more side effect risk.

Andrew Huberman has discussed this publicly in the context of his sleep protocol, specifically noting the discrepancy between what the research supports (0.1 to 0.3mg) and what is sold in pharmacies (3 to 10mg).

Who Should Be Most Cautious

Children and adolescents should use melatonin only under medical supervision, given the potential hormonal effects. The brain and endocrine system are still developing, and regular melatonin supplementation in young people has not been adequately studied for safety.

Pregnant women should avoid melatonin unless advised otherwise by a doctor. Melatonin crosses the placenta and its effects on fetal development are not well understood.

People taking medications that affect the cytochrome P450 enzyme system, which includes many common medications, should be aware that melatonin metabolism can be altered significantly.

When Melatonin Is Actually Useful

Despite its overuse, melatonin has genuinely effective applications. It is one of the best tools for resetting circadian rhythm after jet lag or shift work, used at low doses timed to the destination time zone. It is also useful for delayed sleep phase syndrome, where the circadian clock is shifted and the person struggles to feel sleepy at a conventional bedtime.

For these applications, 0.5mg to 1mg is typically sufficient and appropriate. The key is using it as a timing signal, not as a sedative.

What This Means for Your Sleep

If you are using melatonin and finding it works some nights but leaves you groggy or seems to stop working after a while, the dose is likely the issue. Most people using 5mg or 10mg would get the same or better results from 0.3 to 0.5mg with fewer side effects.

If you are using melatonin every night for general sleep quality improvement rather than for a specific circadian issue, there are better options. For a full breakdown of what works instead, see our guide to melatonin alternatives and our overview of natural sleep supplements with the strongest clinical evidence.