Melatonin and its agonists, circadian rhythms and psychiatry.

The pineal gland has long been implicated in psychiatric disorders, but only after the discovery of melatonin has the physiology behind these theories been better researched and understood, especially its role in chronobiology. The role of melatonin in sleep is well known and the interrelatedness with mood and other disorders is also receiving increasing attention. Circadian rhythm disorders are also common, and often cause psychiatric symptoms, resulting in impairment in daily functioning. Together with other factors, melatonin has an integral role in the pathogenesis and treatment of these conditions. The role of melatonin in various neurological disorders is also of interest and warrants further investigation. Changes in melatonin levels related to ageing have important clinical implications and should be considered in sleep and cognitive disorders in the aged.