Melatonin is a neurohormone, secreted by the pineal gland in the brain, that regulates the sleep/wake cycle. Light suppresses melatonin synthesis. The primary use of melatonin as a supplement is to normalize abnormal sleep patterns.

Irregular sleep patterns are associated with a wide variety of health problems. Melatonin is the hormone used by your body to help you fall asleep, and thus supplementation is seen as a way to help get regular sleep. This is particularly useful for people who engage in shift work or are jet lagged.

Melatonin may also ease symptoms of irritable bowel syndrome (IBS),^[3] reduce tinnitus severity,^[4] lower blood sugar levels in people with type 2 diabetes,^[5] and result in small (perhaps negligible) amounts of weight loss.^[6] There is ongoing research into melatonin supplementation as an adjunct treatment in cancer,^[7] although human studies on the topic are limited.

Some demographics tend to have irregular melatonin production or metabolism in their body. Smokers may be less responsive to supplementation due to increased enzymatic breakdown of the molecule, and older people seem to produce less melatonin during night time. This may be why melatonin seems to have a more consistent effect in older people.^[8]

In typical dosages, melatonin appears fairly safe. Side effects are both uncommon and usually mild, including daytime sleepiness, headache, and nausea. Very rarely, serious adverse effects resulting from melatonin supplementation (often in very high doses) have been reported. Melatonin is not addictive.

As a hormone, melatonin’s main function is to promote the onset and maintenance of sleep. It achieves this by activating melatonin receptors in the brain, which inhibit neuronal activity and regulate the body’s circadian rhythm. Melatonin receptors have been identified in many other tissues as well (including the intestinal tract, pancreas, and immune cells), which may explain some of melatonin’s other health effects.