Melatonin is a hormone produced in the body. It regulates night and day cycles or sleep-wake cycles. Melatonin in dietary supplements is usually produced in the laboratory.

Darkness causes the body to produce more melatonin, which signals the body to sleep. Light reduces the production of melatonin and signals the body to be awake. Some people who have trouble sleeping have low melatonin levels. It is believed that adding melatonin from dietary supplements can help them fall asleep.

People most often use melatonin to treat insomnia and improve sleep in various conditions, such as jet lag. It is also used for depression, chronic pain, dementia and many other conditions.