Melatonin is a hormone that regulates the sleep-wake cycle. It is primarily released by the pineal gland. As a dietary supplement, it is often used for the short-term treatment of trouble sleeping such as from jet lag or shift work. Melatonin can be used to treat delayed sleep phase and circadian rhythm sleep disorders in the blind and provide some insomnia relief. Treat melatonin as you would any sleeping pill and use it under your doctor's supervision.