CoAprovel is a combination of two active substances irbesartan and hydrochlorothiazide. Irbesartan belongs to a group of medicines known as angiotensin-II receptor antagonists. Angiotensin-II is a substance produced in the body that binds to receptors in blood vessels causing them to tighten. This results in an increase in blood pressure. Irbesartan prevents the binding of angiotensin-II to these receptors causing the blood vessels to relax and the blood pressure to lower. Hydrochlorothiazide is one of a group of medicines (called thiazide diuretics) that causes increased urine output and so causes a lowering of blood pressure. The two active ingredients in CoAprovel work together to lower blood pressure further than if either was given alone. CoAprovel is used to treat high blood pressure when treatment with irbesartan or hydrochlorothiazide alone did not provide adequate control of your blood pressure.