What is Spironolactone? Spironolactone is a potassium-sparing diuretic (water pill) that prevents your body from absorbing too much sodium and keeps your potassium levels from getting too low. Spironolactone is used to diagnose or treat a condition in which you have too much aldosterone in your body. Aldosterone is a hormone produced by your adrenal glands to help regulate the salt and water balance in your body.