Looping animation of a melatonin molecule. Atoms are colour_coded spheres carbon: black, hydrogen: silvergrey, oxygen: red, and nitrogen: blue. Melatonin is secreted by the pineal gland in the brain that controls the body磗 biological rhythm. It is secreted at night and induces sleep. Pills containing melatonin can be taken to prevent jetlag. In middle age, melatonin secretion drops off and may be responsible for aging symptoms such as insomnia and irritability.