Does Melatonin Cause Constipation?

Melatonin has emerged as a safe, natural remedy for insomnia and bad sleep. Unlike prescription drugs, it's not addictive and has minimal side effects, notes the Mayo Clinic. Some people may experience mild anxiety, confusion, stomach pain, or tremors after taking melatonin supplements, but these reactions are rare. What you may not know is that melatonin has a direct impact on digestive function.

Besides its role in the sleep-wake cycle, this hormone regulates several functions in your body. Its levels in the gut are about 400 times higher than those in the pineal gland, notes a 2011 review published in the World Journal of Gastroenterology. Therefore, it's not surprising that melatonin regulates digestion and gastrointestinal (GI) motility. Researchers say that it exerts both excitatory and inhibitory effects on the gut, meaning that it can speed up or slow down the passage of food. High doses of melatonin may slow the intestinal transit, while small doses increase peristalsis, or intestinal muscle contractions.

This dietary supplement may benefit those with Crohn's disease, ulcerative colitis, or irritable bowel syndrome (IBS), suggests the above review. The question is, does melatonin cause constipation? After all, it can slow down GI motility when used in large doses. Let's find out!

What's the link between melatonin and constipation?

The human body produces melatonin on its own. Its levels go up in the late evening and begin to gradually decline after 4:00 p.m., explains a 2012 review published in Food and Nutrition Research. This hormone regulates your internal clock, making it easier to fall asleep. Certain factors, such as your age and diet, can affect melatonin synthesis and lead to sleep problems. One way to counteract this issue is to take melatonin supplements, which contain a synthetic version of the hormone. 

Like other health products, melatonin may cause mild adverse reactions ranging from drowsiness to headaches, according to the Mayo Clinic. But constipation is rarely one of them. "As a gastroenterologist specializing in functional gut disorders for 15 years, I have never known melatonin to be a source of constipation," said Dr. Robin Rose in an interview with POPSUGAR. This product can actually improve IBS symptoms, she added.

The problem is that not all melatonin supplements are created equal. Their quality, efficacy, and composition vary among brands. Therefore, it's possible to experience constipation after using this product. "The ingredients in a drug or supplement can change — even what's holding the tablet or the capsule together — and that could cause irritation in your GI system," neurologist Rachel Salas told Women's Health. Some of these ingredients may cause digestive issues. Since there's no way to tell how your body will react to one product or another, you may need to try different brands.