Maelatonin is a hormone secreted by the pineal gland. The pineal gland is a pea like structure located in the centre of the brain. What is now known is that it is part of the body clock, an internal timer that regulates the production of various hormones which in turn control human activities like - sleeping, eating, sexual development, immune systems and maternal insticts.

Plasma Melatonin levels increase steadily between 9 p.m. and 11 p.m. and reaches its peel value between 2 a.m. and 4 a.m. The level of this hormaone then declines and reaches its low level in the afternoon.

Melatonin is synthesized by the pineal gland from the neurotransmitter, serotonin. Serotonin is involved in several central physiological processes, including body temperature and blood-pressure regulation, as well as a variety of neuro-psychological functions such as appetite, memory, and mood. Melatonin and serotonin are inextricably linked: When melatonin levels drop or rise for any reason, so do serotonin levels, and vice versa.