Melatonin is a neurohormone secreted by the pineal gland in the and it is responsible for causing and regulating sleep. Light suppresses melatonin synthesis.
The primary purpose of melatonin as a supplement is to normalize abnormal sleep patterns.
Other benefits of melatonin include general neuroprotective effects, as melatonin is a powerful antioxidant. It does not appear to have much of an effect on lean mass or body fat, but may potentially stop your body from gaining more fat. Melatonin supplementation also benefits eye health, possibly reduces tinnitus, and improve mood (by helping you get quality sleep).
Melatonin’s primary mechanism is by helping decrease the time it takes to fall asleep (as a hormone, that’s its primary job).