Aldactone (Spironolactone) is a diuretic. Diuretics increase the amount of urine passed, which causes the body to lose water and salt. Spironolactone helps to treat high blood pressure. It is not a cure. It also reduces the swelling and water retention caused by various medical conditions, such as heart, liver, or kidney disease. Spironolactone is a potassium-sparing diuretic. It does not make your body lose potassium, it can help patients who have a low blood potassium.