Lithium (Li) is commonly used in treating bipolar disease. Therapeutic concentrations of lithium have almost no psychotropic effects in normal man. It is not a sedative, depressant, or euphoriant and this characteristic differentiates lithium from other psychotropic agents. Prospective epidemiologic studies demonstrate that lithium carbonate in therapeutic oral doses with the plasma level between 1.2 and 1.5 meq/L (225 to 676 mg of lithium) do not cause diabetes insipidus, urine output increases in men to 3 liters; GFR does not significantly increase; creatinine clearance remains stable in women but decreases in men; renal concentrating capacity is significantly reduced; calcium metabolism is altered by lowering urinary calcium excretion and increasing serum calcium concentrations, thereby increasing circulating PTH. In pregnancy Li causes an increase in high perinatal death rate and a high malformation rate. The use of lithium in early pregnancy is associated with a several fold increase in the incidence of cardiovascular anomalies in the newborn, tricuspid valve abnormalities. The woman on lithium therapy who attempts to become pregnant should notify her physician. Careful monitoring of blood lithium levels must be done every three days.