Melatonin, a hormone produced by the pineal gland (located in the middle of the brain), regulates the sleep-wake cycle. Melatonin used in supplements is derived from animals but most is produced artificially. In some countries, melatonin is considered a drug and is regulated as such.
(See also Overview of Dietary Supplements.)
People use melatonin mostly to treat insomnia and to help minimize the effects of jet lag or of shift work. People who are traveling across time zones may take melatonin on the day or night of departure and for 2 to 4 nights after arrival. People who rotate work shifts may take melatonin before going to bed. Research is being conducted in using melatonin to resynchronize the sleep-wake cycle for people in the early phases of Alzheimer disease, as well as for seasonal affective disorder (feeling depressed during winter months).
Evidence suggests that melatonin supplements can affect the sleep-wake cycle. Melatonin supplements also may help certain people with symptoms of jet lag or insomnia.
The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
National Institutes of Health (NIH), National Center for Complementary and Integrative Health: General information on the use of melatonin as a dietary supplement