Hyzaar is used to treat high blood pressure. It is also used to lower the risk of strokes in patients with high blood pressure and an enlarged heart. Lowering high blood pressure helps prevent strokes, heart attacks, and kidney problems. This product contains two medications: losartan and hydrochlorothiazide. Losartan is an angiotensin receptor blocker (ARB) and works by relaxing blood vessels so that blood can flow more easily. Hydrochlorothiazide is a "water pill" (diuretic) that causes you to make more urine, which helps your body get rid of extra salt and water. A valid prescription should be available upon delivery