Diuretics help remove sodium and water from the body. The result of this action is to cause the kidneys to excrete more sodium into the urine. The sodium then draws water from the blood which reduces the circulating volume, thereby lowering blood pressure. Diuretics are used effectively in the treatment of hypertension, and are often prescribed because of their effectiveness, low cost, and few side effects.

Diuretics are used in combination with other drugs to treat edema caused by heart failure, congestive heart failure, cirrhosis, corticosteroid and estrogen therapy, and are especially useful in cases of edema due to renal dysfunction. Although safe, diuretics can also cause unwanted side effects.