MelatoninMelatonin plays a key role in regulating the body's circadian rhythm. Melatonin can be helpful in regulating sleep cycles in individuals who have irregular sleep patterns. Melatonin is a hormone produced by the pineal gland that plays a key role in regulating the bodys circadian rhythms and induction of sleep. It plays an essential role in regulating the sleep cycles, and when supplemented, can be helpful for those who have irregular sleep patterns.