diuretic, drug used to increase urine formation and output. Diuretics are prescribed for the treatment of edema (the accumulation of excess fluids in the tissues of the body), which is often the result of underlying disease of the kidneys, liver, lungs, or heart (e.g., congestive heart failure). They are also used to treat hypertension (high blood pressure) and glaucoma. They act on the kidneys, modifying the absorption and excretion of water and electrolytes such as sodium and potassium. Types of diuretics include thiazides, loop diuretics, and potassium-sparing diuretics.