Skip to main content
Drug Info

Melatonin side effects and how to avoid them

The most common melatonin side effect is sleepiness, which is why most people take the supplement
SingleCare logo
By | Oct. 23, 2023 Medically reviewed by Anne Jacobson, MD, MPH
A bed: What are the side effects of melatonin?

Key takeaways

  • Melatonin is primarily used as a sleep aid and is considered the first-line pharmacological treatment for sleep initiation problems, with fewer side effects compared to other sleep aids.

  • Common side effects of melatonin include daytime drowsiness, headache, dizziness, and nausea, with more serious side effects being highly uncommon at recommended doses.

  • Melatonin interactions with CNS depressants, opioids, alcohol, and certain medications can increase the risk of excessive sedation, and its use is advised with caution in pregnant women, breastfeeding mothers, and individuals with certain health conditions.

  • To avoid melatonin side effects, it is recommended to follow dosing instructions, start with a low dose, avoid alcohol and CNS depressants, not use melatonin habitually, choose supplements carefully, and consider lifestyle changes for sleep issues.

In this article:

Melatonin is a popular dietary supplement that is mainly used as a sleep aid. The brain’s pineal gland naturally makes melatonin, which signals the brain to sleep. But, some people have low melatonin levels or circadian rhythm problems, like jet lag and shift-work sleep disorder, making falling asleep difficult. In those situations, healthcare providers may recommend melatonin and lifestyle interventions to help patients fall asleep faster, stay asleep longer, and sleep better. Since melatonin has fewer side effects than other sleep aids, the American Academy of Family Physicians considers it the first-line pharmacological treatment for people who have problems falling asleep. It’s also prescribed to treat other health conditions, such as post-traumatic brain injury and some neurodegenerative diseases, and as an additional treatment for migraines, endometriosis, and some kinds of cancers.

Melatonin is available over the counter without a prescription. This makes it different from Rozerem (ramelteon), which is a prescription medication that works on the same brain receptors as melatonin. 

Common side effects of melatonin

The most common side effects of melatonin include:

  • Daytime drowsiness 
  • Headache 
  • Dizziness 
  • Nausea

Less common side effects of melatonin include:

  • Nightmares or vivid dreams
  • Short-term depression or mood swings
  • Irritability
  • Abdominal cramps and diarrhea
  • Constipation
  • Decreased appetite
  • Nighttime urinary incontinence
  • Increased risk of falls and seizures
  • Increased risk of seizures
  • Disorientation
  • Reduced alertness

Keep in mind that clinical studies use controlled doses and monitor participants taking the supplement. The doses are varied but often aren’t excessive. Outside of clinical studies, melatonin is unregulated. People may decide to take more than the recommended amount or take it for a longer period of time. Taking high doses or using melatonin supplements chronically is more likely to produce higher rates of side effects. 

Melatonin and weight 

People may gain weight for a variety of reasons, but in general, melatonin doesn’t appear to be one of them. In fact, some studies have shown that melatonin may help support a healthy weight. One study in particular found that melatonin supplementation led to weight loss in postmenopausal women.

Melatonin and the digestive system

Melatonin is produced not only in the brain but also in the digestive system, where it regulates many important tissue processes. Increased melatonin in the gut may cause nausea, diarrhea, constipation, or cramps in some people. However, keep in mind that individuals have unique responses to drugs and supplements. 

Melatonin and daytime sleepiness

A systematic review of melatonin use in older adults found the most likely side effect was daytime sleepiness. If melatonin supplements cause daytime sleepiness or impairment, do not drive or operate heavy machinery until you feel better. 

Serious side effects of melatonin

While serious side effects are highly uncommon in adults taking melatonin at recommended doses, it’s important to be aware of how a drug or supplement affects you individually. Older adults and people who take other medications should be especially cautious if they feel sleepy or dizzy. 

How soon do melatonin side effects start?

Melatonin promotes sleep, so drowsiness and sleepiness are early side effects of the supplement. Healthcare providers suggest that melatonin be taken an hour and a half or two hours before bedtime since side effects like drowsiness peak at one and a half hours after taking it. 

How long do melatonin side effects last?

Melatonin supplements have a half-life of three and a half hours. That’s the amount of time it takes for half a dose of melatonin to be cleared from the body. If taken an hour and a half to two hours before bedtime, side effects like drowsiness should disappear by the time people wake up in the morning. However, sleepiness and drowsiness can persist into the next day.

What are the long-term side effects of melatonin?

Regular daily use of melatonin has no known long-term side effects. However, one small study of eight men found that regular use of melatonin decreased sperm concentration and motility in men.

Melatonin interactions

The most common effect of melatonin is drowsiness, which is why people take it to promote sleep. For this reason, drugs that cause sedation—particularly sleep medicines and benzodiazepines—can increase the risk of excessive sedation when taken with melatonin.

However, any central nervous system (CNS) depressant can cause excessive sleepiness when taken with melatonin. This includes opioids, alcohol, and over-the-counter (OTC) antihistamines. In addition, hormonal birth control increases the body’s natural levels of melatonin, so taking melatonin supplements may increase the likelihood of related side effects. 

Melatonin does more than just promote sleep. It has many effects throughout the body. For this reason, melatonin may affect the effectiveness of drugs like:

Safety measures while using melatonin

Melatonin has no absolute contraindications. However, melatonin drug labels advise certain people to consult their healthcare provider before taking melatonin supplements. This includes:

  • Pregnant women
  • Women who are breastfeeding
  • People taking prescription medication
  • Children and adolescents

Other people should be cautious about taking melatonin or taking high doses of it. This includes people with:

  • Kidney disease
  • Liver disease
  • Seizure disorders
  • Autoimmune conditions

Melatonin increases immune system activity, so it may increase the risk of flare-ups in people with autoimmune disorders.

Melatonin and children

Because the active ingredients in supplements can vary widely, the American Academy of Sleep Medicine has issued an advisory on the use of melatonin in children. Always talk to a healthcare provider before giving a child or adolescent melatonin supplements.

Melatonin during pregnancy

There’s little research on the safety of melatonin during pregnancy, so the risks are unknown. Talk to a healthcare provider before taking melatonin supplements if you are or may become pregnant.

Melatonin while breastfeeding

As with pregnancy, there’s little research on the safety of taking melatonin when breastfeeding. Breast milk already contains natural melatonin, but it’s unknown whether taking melatonin supplements increases the amount of melatonin in breast milk. Melatonin supplements may also contain other ingredients, impurities, and contaminants that may not be healthy for an infant. The Food and Drug Administration advises women who are breastfeeding to talk to a healthcare provider before taking melatonin supplements.

Melatonin dependence

Melatonin supplements do not cause dependence or withdrawal symptoms.

Melatonin overdose

Serious side effects in adults who take large amounts of melatonin are uncommon. However, children are at higher risk for serious side effects or death from melatonin overdose. Call a poison helpline or get medical attention if you suspect someone has taken too much melatonin.

Melatonin recalls

Melatonin is a popular supplement available in many brand-name and generic products. There have been numerous recalls of individual melatonin products for impurities, poor quality, or incorrect labeling. To date, there has been no industry-wide recall of melatonin supplements. 

How to avoid melatonin side effects

Melatonin is a relatively safe supplement. It has fewer side effects than other sleep aids. Even though most side effects are mild, they can be minimized by following a few simple rules:

1. Take melatonin supplements as instructed

Like other dietary supplements, melatonin supplements often come with a few instructions. Most will have a suggested dose and schedule. This should indicate the maximum dose and the time you should take it. If there are concerns about side effects, get medical advice from a healthcare professional. 

2. Start with a small dose

There are no standardized melatonin doses for any medical condition or sleep issue. Doses can range from very small (0.5 mg) to very large (60 mg), depending on the product. The best advice is to start small. The American Academy of Family Physicians advises low doses—1 mg taken before bedtime. That’s probably a good place to start if side effects are a concern. If that dose doesn’t work, increase the dose slowly until an optimal dose is reached. Don’t exceed the maximum recommended dose.

3. Avoid alcohol

Alcohol will not only worsen the sedative effects of melatonin, but it will also decrease sleep quality. As most people know, few wake up feeling refreshed after drinking alcohol. The additional sedation will raise the risk of injuries or accidents.

4. Avoid CNS depressants 

Like with alcohol, melatonin increases the sedative effects of other CNS depressants like sleeping pills, benzodiazepines, and sedating antihistamines. Taking melatonin with CNS depressants increases the risk of injuries or accidents.

5. Don’t make melatonin a habit 

Healthcare providers believe melatonin is safe for short-term use to address sleep problems caused by internal sleep clock disruptions. Melatonin is not a sleeping pill and doesn’t work instantly. If melatonin supplements are not fixing a sleep problem, talk to a healthcare professional. 

6. Don’t buy just any melatonin supplement 

The supplement industry is poorly regulated. Consumers are not always sure of what they’re getting in a supplement. One study found that melatonin supplements had anywhere from one-sixth to almost five times the amount of melatonin advertised on the label, even among individual doses in the same bottle. It’s even more difficult to figure out whether there are impurities or active contaminants in the supplement. One solution is to look up the supplement on the website of a third-party tester, like the United States Pharmacopeia (USP). A USP-verified mark should be the minimum criterion when purchasing supplements. Getting medical advice from a healthcare professional is an even better place to start.

How to treat side effects of melatonin

Most side effects of melatonin are temporary and will resolve before a person wakes up. Some can’t be helped, like sleepiness, daytime drowsiness, or vivid dreams. The first way to handle these problems is by reducing the dose. If you get a headache from melatonin, OTC pain medications may help. You can prevent potential nausea side effects by taking melatonin with food or using an OTC nausea relief medication.

Bottom line: Is melatonin safe?

Melatonin is considered safe for temporary use in most adults to address sleep issues due to internal clock discrepancies or low melatonin levels. It’s not considered effective for general insomnia, but it’s not unsafe, either. Most side effects are mild and temporary. Severe side effects are uncommon in adults. There are drug interactions, but none that are contraindications. Try changes to your bedtime routine before or along with adding melatonin. And as with every other type of OTC supplement or medicine, if there are any doubts, get medical advice from a healthcare professional.

Sources