Drinking, thirst and water intoxication.

Drinking is an activity determined partly by oropharyngeal stimulation and gastrointestinal sensations as well as biochemical changes, and thirst need not be involved. It is sometimes disturbed in mania or depression. Overdrinking (polydipsia) is common in long-stay in-patients, but only gives rise to water intoxication when there is a variable functional renal abnormality such as SIADH causing water retention. In contrast, in affective disorders, disturbance of sodium retention may be seen, possibly representing failure of nervous vascular control as part of the mental illness.