Surprising Side Effects of Taking Melatonin Supplements, Says Science
Melatonin is a hormone that is produced in the brain. It regulates the body's circadian rhythm, hormones secreted by the endocrine system, and sleep patterns.
Experts may recommend a melatonin supplement for certain conditions like jet lag or insomnia, but those supplements are synthetically made in a laboratory. (For natural sleep-supporting supplements, check out these 5 Absolute Best Foods to Eat For Better Sleep.) Usually, the supplements come in pill form, but they can also be found in a form that you place in the cheek or under your tongue so it gets absorbed quickly into the body.
If you're looking to take melatonin, here are 5 side effects that you may experience.
Helps You Fall Asleep
Some folks have trouble falling asleep at a usual bedtime. Research shows that taking melatonin supplements can help reduce the length of time young adults and kids fall asleep (in those who have trouble falling asleep). It should be noted that this supplement is not regulated by the Food and Drug Administration (FDA) and should only be used in children and adults after speaking with a medical doctor.
Sign up for our newsletter!
Can Cause Daytime Sleepiness
If you take melatonin during the day, it can cause sleepiness. This is why when you take it matters. It is advised not to drive or use machinery for 4 to 5 hours after taking the supplement.
Can Lead to Gastrointestinal Symptoms
When taken orally, melatonin has been reported to have side effects like nausea, abdominal cramps, mild abdominal pain, diarrhea, decreased appetite, and/or constipation. Oftentimes these symptoms happen within the first few days of taking the supplement and then subside after a few days.
May Cause Migraine Headaches
When taken orally, melatonin has been reported to cause migraine-like headaches or dizziness, especially during the first few days. The symptoms tend to be more common when melatonin is taken in the morning or at high doses (greater than 50mg).
Help with Jet Lag
Taking 2 to 3 milligrams of melatonin daily when traveling to a different time zone seems to improve alertness and reduce daytime sleepiness in those with jet lag. There is also some evidence that melatonin supplements may help improve other jet lag symptoms including fatigue.
Abnormally Low Blood Pressure
While it's a less common side, for some, melatonin can cause hypotension—also known as abnormally low blood pressure—according to Mayo Clinic. Some studies have found that taking the supplement may reduce blood flow and autonomic cardiovascular regulation, but this usually only occurs when a person is already experiencing untreated hypertension.
A previous version of this article was originally published on August 25, 2021.
