Melatonin side effects: is melatonin safe?

Picture this: You get into bed at a reasonable hour, fall asleep with ease, then wake up feeling refreshed eight hours later. For many people, such a scenario is what dreams are made of. But melatonin may be able to help. 

Many people are wary about taking anything to help them sleep—understandably so! Melatonin is a natural substance (our bodies make it naturally), but like any supplement, it has the potential to cause some side effects. 

Here’s what you need to know about melatonin’s side effects, the conditions it’s used for, and how to take it.

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Melatonin is considered a relatively safe and non-toxic supplement to help you sleep better, although some possible side effects have been reported. These usually occur with high doses or extended-release formulations, including (Savage, 2021):

• Daytime drowsiness

• Changes in blood pressure causing dizziness

• Headaches

• Nausea

Who shouldn’t take melatonin? 

Certain people should avoid using melatonin supplements. These include people taking other sedating medicines such as benzodiazepines or zolpidem. You should also not take melatonin if you are pregnant or breastfeeding because we don’t know if it’s safe for a growing fetus (Savage, 2021).

Other types of people should be cautious and talk to their healthcare provider before using melatonin. If you are on dialysis for kidney disease, there is a greater risk for side effects because dialysis doesn’t completely remove melatonin from your bloodstream (Savage, 2021).

Melatonin is unlikely to cause liver injury, but people with impaired liver functioning should still be careful. Your liver might not be able to process the levels of melatonin in your bloodstream as well as in someone without liver disease (Savage, 2021).

You should consult a healthcare provider if you have an autoimmune condition or have had an organ transplant. Melatonin can stimulate your immune system. Researchers aren’t sure how much of an effect this will have, but it’s best to use caution if you have one of these conditions or take immunosuppressant medicines (Savage, 2021).

Melatonin is a hormone produced naturally by your body, best known for its role in promoting sleep. You can also take additional melatonin as a dietary supplement in pill form. 

To make melatonin naturally, your body starts with tryptophan (the sleep-inducing amino acid most commonly associated with your Thanksgiving dinner). It then changes it into serotonin (known as the feel-good hormone) in your brain. Some of that serotonin makes its way to the pineal gland in your brain, where it’s converted into melatonin depending on your body’s circadian rhythms (Savage, 2021).

The circadian system regulates many processes in your body necessary for health, including when you feel wakeful or sleepy. Your circadian rhythm has a natural cycle that averages around 24 hours. One of the main ways this cycle is regulated is through the presence of light and dark (Basit, 2021).

How much melatonin your brain makes depends on the information it gets about how much light is being processed by the retinas in your eyes. The amount of melatonin produced by your body increases in the evening as the light dims and peaks about three hours before you get up in the morning (Savage, 2021; Basit, 2021).

Since this system is so dependent on external cues such as light, any disruptions in the amount of light present or your body’s ability to sense it can throw melatonin production off schedule. This, in turn, can affect your ability to get a good night’s sleep (Savage, 2021, Basit, 2021).

Melatonin supplements have been used to treat a wide range of health conditions, mostly related to sleep problems. Insomnia, jet lag, non-24 disorder, and shift work sleep disorder are among the most well-studied uses for melatonin.

Insomnia

Being unable to fall or stay asleep is the most common reason that people take melatonin. Studies of melatonin use have been small but high-quality. They have shown it may be as effective—or possibly even more so!—as sleep medications for people with insomnia. In addition, the side effects of melatonin for insomnia were uncommon and not serious (Costello, 2014).

Jet lag

Jet lag is a type of temporary sleep disorder that happens when you travel across time zones. It occurs when your body’s internal clock gets out of sync with your current location’s light/dark cues and mealtimes. It can cause fatigue, trouble sleeping, and difficulty concentrating.

An analysis of eight randomized controlled trials looked at using melatonin to counteract the symptoms of jet lag. Researchers found that melatonin worked the same as or better than a placebo for rebalancing the sleep-wake cycle in people with jet lag. There were occasional, but not serious, side effects reported, such as tiredness the following day (Costello, 2014).

Non-24 disorder

Non-24-hour sleep-wake disorder is a circadian rhythm sleep disorder where your biological clock fails to sync to a 24-hour day. Instead of sleeping at roughly the same time every day, you’ll find your sleep time gradually delayed by minutes to hours every day. This is mainly seen in people who are totally blind and unable to perceive light-dark cues. Treatment involves using medications and supplements that affect the body’s melatonin levels to train your body’s circadian rhythm to a regular schedule (Basit, 2021).

Shift work sleep disorder

Shift work sleep disorder is another type of circadian rhythm sleep disorder that stems from working long or irregular hours outside of the standard 9–5. Your body has trouble adjusting to a schedule that doesn’t match your body’s internal clock and causes you to have difficulty falling asleep and staying asleep.

Shift workers commonly use melatonin to help regulate their sleep patterns, although the medical research isn’t conclusive about its long-term effects. Most trials didn’t favor either melatonin or the placebo. Melatonin has been found to be a relatively safe choice, though, with no severe side effects or interactions, in people with shift work sleep disorder (Costello, 2014).

One benefit of melatonin is that it’s readily available over-the-counter in most pharmacies in the United States.

Additionally, many human and animal studies show that short-term use of melatonin is safe and causes no serious adverse effects. Even long-term use in adults only shows mild side effects compared to placebo treatments (Andersen, 2016).

Melatonin is also non-habit-forming. No studies have shown that people become dependent on melatonin over time (Savage, 2021).

Since the Food and Drug Administration (FDA) doesn’t regulate melatonin as a medication, there are no official dosing guidelines. The doses used in most research studies varied from 0.1 mg to 10 mg, given up to two hours before bedtime (Savage, 2021).

Melatonin can be used in children and teenagers, but only after a trial of good sleep practices has failed. Good sleep hygiene includes (Cummings, 2012):

• A consistent bedtime

• A dark, quiet space

• Avoiding electronics and stimulants before bed

• Switching to quiet activities, such as reading, before bed

While some studies have been done in these younger groups, they have typically been shorter and haven’t typically had very many participants. So our knowledge about the long-term safety of treatment with melatonin for children and teens is limited. There is also some conflicting research about whether melatonin can delay the start of puberty (Cummings, 2012). If you want to give your child melatonin, be sure to speak with your pediatrician first for guidance.

There also isn’t a lot of research into using melatonin with older adults. Seniors seem to process melatonin supplements differently, and the levels in the body can be harder to control. Researchers advise using the lowest dose of immediate-release melatonin possible for older adults. Recommended doses range from 0.3 mg to a maximum of 2 mg, one hour before bedtime. Controlled release formulas aren’t recommended for older adults to minimize melatonin side effects (Vural, 2014).

One last concern with melatonin supplements is to ensure you buy a high-quality brand to be confident you are getting the amount of melatonin you want. An analysis of 31 melatonin supplements found a considerable variation in the amount of melatonin the supplements actually contained. The melatonin content was more than 10% above or below the labeled amount in more than 71% of the products tested (Erland, 2017).

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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

October 29, 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.