Melatonin

Melatonin is a hormone produced by the pineal gland, located in the center of the brain. It is a derivative of the amino acid tryptophan.

Melatonin helps regulate sleep-wake or circadian rhythms. Normally, production of melatonin by the pineal is stimulated by darkness and inhibited by light.

In recent times, melatonin has become available as a drug and a supplement. It appears to have some use against insomnia and against jet lag.