Hydrochlorothiazide (HCTZ) (hye droe klor oh THYE a zide) treats high blood pressure. It may also be used to reduce swelling related to heart, kidney, or liver disease. It helps your kidneys remove more fluid and salt from your blood through the urine. It belongs to a group of medications called diuretics. This medicine may be used for other purposes; ask your health care provider or pharmacist if you have questions.