polydipsia /pol′ēdip″sē·ə/ [Gk, polys + dipsa, thirst] , 1. excessive thirst. It is characteristic of several different conditions, including diabetes mellitus, in which an excessive concentration of glucose in the blood osmotically pulls intracellular fluid into the bloodstream and increases the excretion of fluid via increased urination, which leads to hypovolemia and thirst. In diabetes insipidus the deficiency of the pituitary antidiuretic hormone results in excretion of copious amounts of dilute urine, reduced fluid volume in the body, and polydipsia. In nephrogenic diabetes insipidus there is also copious excretion of urine with consequent polydipsia. Polyuria resulting from other forms of renal dysfunction also leads to polydipsia. The condition also may be psychogenic in origin. 2. (Informal) alcoholism.
