Cozaar is used in the treatment of high blood pressure. It is effective when used alone or with other high blood pressure prescriptions, such as diuretics that help the body get rid of water. Cozaar is the first of a new class of blood pressure prescriptions called angiotensin II receptor antagonists. Cozaar works, in part, by preventing the hormone angiotensin II from constricting the blood vessels, which tends to raise blood pressure. Used to treat high blood pressure.