Diabetes insipidus – a condition characterized by excessive urination. The urine is severely dilute and the patient characteristically has excessive thirst. Fluid restriction has no effect on the degree of dilutation in the urine. The most common reason is central DI due to a lack of diuretic hormone (ADH or arginine vasopressin) but DI can also occur due to an insensitivity to ADH in the kidneys (nephrogenic diabetes insipidus or as a result of a drug being administered.