Melatonin is a naturally occurring hormone produced by the pineal gland that plays a role in the regulation of the sleep-wake cycle. The pineal is embedded in the brain and receives signals via the optic nerve. Melatonin is secreted by the gland after the body senses darkness at the end of each day to keep our bodies synchronized with the rhythms of day and night. Melatonin is often used as a home remedy for jet lag.