Melatonin is a hormone produced by a small gland in the brain to help the body regulate the natural cycle of sleeping and waking. Small amounts of melatonin are found in some foods, and it is also available in dietary supplements.
Natural melatonin production is partly affected by light, since melatonin levels are higher at night than during the day. During the shorter days of the winter months, melatonin production may start earlier or later, causing the body to feel as if it needs more sleep.
Melatonin is used to treat jet lag and insomnia. A low dose taken at a certain time during the day may also be effective for easing symptoms of seasonal affective disorder (SAD).
Melatonin supplements are generally safe for short-term use. The safety and effectiveness of long-term use is still being assessed.
WebMD Medical Reference from Healthwise