Benzthiazide is a thiazide diuretic used primarily to treat hypertension and fluid retention (edema) associated with heart failure, kidney disorders, or other conditions. It works by inhibiting the reabsorption of sodium and chloride in the distal convoluted tubule of the kidney, which increases urine production and helps the body eliminate excess salt and water. This reduces blood volume, lowers blood pressure, and contributes to improved cardiovascular function. It is often used in combination with other antihypertensive medications for enhanced therapeutic effect.