Melatonin and the pineal gland. Computer artwork of a sectioned human brain in side view, depicting secretion of the hormone melatonin by the pineal gland (highlighted). The chemical formula for melatonin is shown. Front of the brain is at left. Melatonin is a hormone secreted in the blood which controls the body's biological clock. It is produced naturally by the pineal gland in the brain. Secreted at night, melatonin helps induce sleep and set the biological rhythm of the body. In middle age, melatonin secretion drops off and may be responsible for aging symptoms such as insomnia and irritability. Melatonin as a drug is used to prevent jetlag and may help to slow aging.