The patient drinks large amounts of water, which raises the pressure of the extracellular medium. As a side effect, the antidiuretic hormone level is lowered. The urine produced by these patients will have a low electrolyte concentration and it will be produced in large quantities (polyuria). If the patient is institutionalised, close monitoring by staff is necessary to control fluid intake. In extreme episodes, the patient’s kidneys will be unable to deal with the fluid overload, and weight gain will be noted.