Olmesartan Medoxomil + Chlorthalidone is a combination of two medicines: Olmesartan and chlorthalidone which lower blood pressure effectively. Olmesartan is an angiotensin receptor blocker (ARB). It works by blocking the hormone angiotensin thereby relaxing blood vessels. This allows the blood to flow more smoothly and the heart to pump more efficiently. Chlorthalidone is a diuretic that removes extra water and certain electrolytes from the body. Over time it also relaxes blood vessels and improves blood flow.