Melatonin Side Effects and Safety 101

Can’t sleep and looking for a nonhabit-forming sleep aid?

It’s not unusual to deal with insomnia from time to time. You may have difficulty falling asleep. Or if you’re able to fall asleep quickly, you may wake up after two or three hours. This can cause daytime sleepiness, irritability, and decreased productivity.

One night of bad sleep might not wreak too much havoc on your body. But when the problem goes on for days, weeks, or months, supplementing with melatonin can get your sleep back on track.

Melatonin is a hormone that your body makes naturally. Your melatonin level increases a couple of hours before bedtime, which signals your body to prepare for rest. (1) It’s important to note, however, that melatonin isn’t a sleep initiator but rather a sleep regulator, explains Carolyn Dean, MD, a sleep expert and author of 365 Ways to Boost Your Brain Power: Tips, Exercise, Advice.

Melatonin needs vary from person to person. On average, most people need less than 3 milligrams (mg) per night to sleep better. Yet some people take more. (3)

Melatonin is generally safe for short-term use of one to two months in most healthy adults. But some people are more sensitive to the oral hormone and experience side effects. Adverse effects tend to occur with long-term use or when a person takes too much. (2,4)

Possible side effects of oral melatonin include: (1,3,5)

Headache A mild to moderate headache can indicate that you’ve taken too much or that your body is sensitive to oral melatonin.
Stomach Problems Melatonin also causes stomach discomfort in some people. This may include cramps, nausea, and diarrhea.
Dizziness Some people who take melatonin also report mild dizziness, lightheadedness, or vertigo.
Irritability Too much melatonin can also affect mood. You may feel cranky, anxious, or have periods of depression.
Drowsiness Even though melatonin doesn’t usually cause a “hangover effect,” some people do experience daytime drowsiness. This can reduce alertness and make it difficult to drive or operate machinery. If you take melatonin, wait at least five hours before operating machinery. Keep in mind that some medication may intensify drowsiness, such as depressants and selective serotonin reuptake inhibitors. (1)
Low Blood Pressure Sometimes, melatonin causes abnormally low blood pressure. Melatonin side effects are usually mild. (6) However, untreated low blood pressure can lead to life-threatening complications. Low blood pressure means that your body can’t carry enough oxygen to your organs. This can affect heart and brain function. Symptoms of low blood pressure include dizziness, fainting, blurry vision, confusion, and fatigue. (7)

If you experience mild side effects of oral melatonin, reduce your dosage to see if symptoms improve. Talk with your doctor about your dosage if your symptoms persist or worsen. Everyone’s body is different. So while one person may be able to tolerate 3 mg of melatonin a night, another person may be able to tolerate only 1 mg.

When used properly, oral melatonin is safe for most adults. Since the supplement helps regulate sleep, it can be taken for different circadian rhythm conditions. For example: (8,9)

Jet Lag Traveling through different time zones can cause temporary sleep problems in which your body's internal clock gets out of sync. This can reduce sleepiness or affect the quality of sleep.
Delayed Sleep Phase Disorder With this disorder, your nightly sleep might be delayed by several hours compared with the average person’s. So instead of your body preparing to fall asleep between 9 p.m. and 11 p.m., your body may not naturally feel sleepy until 2 a.m. or later. As a result, you may get only a few hours of sleep each night.
Shift Work Disorder If you work overnight and sleep during the day, you may have difficulty falling asleep. Melatonin can help enhance the quality of daytime sleep.
Insomnia This is an inability to fall asleep or stay asleep during the night. There are different underlying causes for insomnia, such as depression, anxiety, and pain. Melatonin helps induce sleep for occasional insomnia.
Sleep Disorders in the Blind Because totally blind people can’t perceive light, they may have difficulty falling asleep and staying asleep. Melatonin can help restore sleep patterns in the blind, improving their sleep quality.

Adults aren’t the only ones with acute or chronic sleep problems. Melatonin is also safe for children who have difficulty sleeping due to insomnia, circadian rhythm disorders, attention deficit disorder/attention deficit hyperactivity disorder (ADD/ADHD), autism, and other neurological disorders.

Dosing for children varies. Some children may need only 1 to 3 mg a night, whereas a child with ADHD or autism may need 3 to 6 mg per night. But because oral melatonin is a supplement and is not regulated by the U.S. Food and Drug Administration, experts caution that parents should consult with a doctor before allowing children and adolescents to try melatonin. (10,11)

Your doctor can help you understand whether melatonin is right for your child and review the risk of side effects. “Side effects reported for children include nausea, diarrhea, headaches, changes in mood, sleepiness the next day, and bed-wetting,” notes Dr. Dean.

Some herbal and dietary supplements can interact negatively with prescription medication, and melatonin is no exception.

Before you take this supplement to improve the quality of your sleep, speak with your doctor.

Melatonin doesn’t interact with every prescription drug, but it can make some medicines less effective, like blood pressure and seizure medication. It can also boost blood sugar and is therefore not recommended for people with diabetes, warns Dean.

The supplement can also interact with blood-thinning medication, immunosuppressants, and corticosteroids. There’s also the risk of increased drowsiness when taken with birth control pills, depressants, or selective serotonin reuptake inhibitors. (1)

If you have chronic pain due to an inflammatory disease, melatonin might seem like a safe solution for better sleep. But this supplement isn’t recommended for people who have an autoimmune disease like lupus or arthritis. (12)

Melatonin can stimulate the immune system, triggering an inflammatory response and worsening these diseases.

There is no definitive research on the safety of using melatonin during pregnancy or while breastfeeding, so experts recommend talking to your doctor if that’s something you want to consider. (13)

Melatonin is preferred by some because it’s nonhabit-forming and a natural sleep aid. But the supplement isn’t right for everyone, and side effects can occur if not taken properly.

If you experience side effects, reduce the amount you take. If symptoms continue, stop taking oral melatonin. Also, don’t forget to consult your doctor before combining melatonin with a prescription medication.

For the most part, melatonin should be used only as a short-term remedy. See your doctor or a sleep specialist if sleep problems worsen or don’t improve after a few months.

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