Psychogenic polydipsia is an uncommon clinical disorder characterized by excessive water-drinking in the absence of a physiologic stimulus to drink. The excessive water-drinking is well tolerated unless hyponatraemia supervenes (1). The level of hyponatraemia used in one study was below 130 mmol/L (2). Classically this disorder has been described in hospitalised schizophrenics. Also it may occur in children, as a symptom of emotional difficulties or as an isolated phenomenon in a child who simply enjoys drinking.
The diagnosis of psychogenic polydipsia is one of exclusion and requires specialist investigation and management; the most important test is the water deprivation test which should be undertaken carefully. Note that chronic psychogenic polydipsia may actually impair the response of the kidneys to ADH, and therefore reduce the renal concentrating ability. Equivocal results should be interpreted with caution.
Clozapine is an atypical antipsychotic drug that has been demonstrated to be a highly effective treatment for polydipsia in schizophrenic patients. There has also been the successful use of clozapine in psychogenic polydipsia in a non-schizophrenic patient (3).