Spironolactone (brand name Aldactone) is used to lower blood pressure. It’s a prescription diuretic medication or “water pill.” It helps you get rid of excess fluid and sodium but keeps potassium in the body. Spironolactone primarily works by blocking the activity of aldosterone (aldosterone antagonist). Aldosterone is a hormone made by the adrenal glands (small glands that sit on top of your kidneys) that encourages sodium and fluid retention. By blocking aldosterone, spironolactone helps you excrete water and sodium—this decreases your overall fluid volume. Here’s more on what you need to know about spironolactone , its primary uses, and what side effects to be aware of before taking the drug.