Melatonin is a hormone that is produced by the pineal gland, a small gland located in the brain. Very small amounts of melatonin are also found in foods such as meats, grains, fruits, and vegetables.

Some people take melatonin to treat jet lag or sleep problems. Scientists are studying other possible benefits of melatonin, such as for people with sleep disorders, those with winter depression or seasonal affective disorder (SAD), and people who work evenings, nights, or alternate shifts.

Scientists believe that very small doses of melatonin taken at certain times of the day help reset the body's 24-hour clock, or circadian rhythms. But its safety and effectiveness have not been thoroughly tested. Although melatonin occurs naturally in our bodies, taking large doses of it may cause undesirable side effects, such as sleep disruption and daytime fatigue. Very large doses of melatonin may also inhibit a woman's ovulation by disturbing hormone levels.

The body's natural melatonin may help some people to fall asleep, but it's not clear whether supplemental melatonin will help you fall asleep or remain sleeping during the night. More studies of melatonin's effect on chronic insomnia are needed. For more information, see the topic Insomnia.