blocker Vasopressin receptor antagonists, such as conivaptan Acetazolamide, a carbonic anhydrase inhibitor Lithium was previously used for treatment of PPD as a direct competitive ADH antagonist, but is now generally avoided due to its toxic effects on the thyroid and kidneys. It is important to note that the majority of psychotropic drugs (and a good many of other classes) can cause dry mouth as a side effect, but this is not to be confused with true polydipsia in which a dangerous drop in serum sodium will be seen. Terminology In diagnosis, primary polydipsia is usually categorised as: Psychogenic (PPD) – caused by underlying psychiatric symptoms, including those caused by psychoses and rarely by affective disorders Non-psychogenic – another non-psychological cause, including idiopathic (unknown cause) The terms primary polydipsia and psychogenic polydipsia are sometimes incorrectly used interchangeably – to be considered psychogenic, the patient needs to have some other psychiatric symptoms, such as delusions involving fluid intake or other unusual behaviours. Primary polydipsia may have physiological causes, such as autoimmune hepatitis. Since primary polydipsia is a diagnosis of exclusion, the diagnosis may be made for patients who have medically unexplained excessive thirst, and this is sometimes incorrectly referred to as psychogenic rather than primary polydipsia. Non-psychogenic Although primary polydipsia is usually categorised as psychogenic, there are some rare non-psychogenic causes. An example is polydipsia found in patients with autoimmune chronic hepatitis with severely elevated globulin levels. Evidence for the thirst being non-psychogenic is gained from the fact that it disappears after treatment of the underlying disease. Non-human animals Psychogenic polydipsia is also observed in some non-human patients, such as in rats and cats. See also Water intoxication Fluid deprivation test References Further reading External links Psychogenic Polydipsia (Excessive Fluid seeking Behaviour) by Donald "Don" Hutcheon on the APA's website Symptoms and signs of mental disorders Thirst Schizophrenia