Melatonin is a naturally occurring hormone produced by the pineal gland that regulates the body's sleep-wake cycle, also known as the circadian rhythm. Its release is stimulated by darkness and suppressed by light, signaling to the brain that it is time to sleep by interacting with MT1 and MT2 receptors in the suprachiasmatic nucleus (SCN) of the hypothalamus. Melatonin’s primary role is to promote relaxation, decrease body temperature, and help synchronize biological processes with the night-day environmental cycle, making it a widely used over-the-counter supplement for sleep disorders and circadian rhythm disturbances.