Thiazide diuretics are used to treat high blood pressure, heart failure, and edema (swelling). Thiazide diuretics work by helping your kidneys remove extra salt and water from your body, which helps to lower blood pressure and reduce swelling. These medications are usually taken as oral pills. Examples include hydrochlorothiazide (Microzide) and chlorothiazide. You can choose the form that best fits your needs.