Melatonin is a hormone produced by the pineal gland and has an significant role in circadian rhythms. The daily rhythm of melatonin secretion is controlled by a built-in, free-running pacemaker, the suprachiasmatic nucleus , and is synthesized from the amino acid tryptophan. Melatonin synthesis is controlled by contact with cycles of light and dark, and occurs independently of sleep.

Melatonin promotes sleep and its secretion increases when takes place the onset of darkness, helping to keep us asleep at night. Melatonin production usually peaks between midnight and 2am, then starts to fall and is low during the day. It also helps decrease core body temperature, which helps induce sleep. However, sleep is possible even when melatonin levels are low. People who have their pineal gland removed have only negligible disruption in sleep.


Laboratory experiments have shown that melatonin has antioxidant effects and suppresses the growth of some cancer cells. Laboratory researches also show it has anti-inflammatory effects. When melatonin is administered as a drug it has been proved to decrease levels of the female hormones progesterone and estradiol. It also enhances the secretion of prolactin (hormone produced by the pituitary gland). Melatonin may decrease the sensitivity of the body to insulin, which can raise blood sugar levels.