Hypertension tablets. Blister pack of 4 milligram tablets of the blood vessel widening (vasodilator) drug Cardura (doxazosin). It is taken to decrease high blood pressure (antihypertensive). Cardura works by blocking the effect of the body chemical noradrenaline, which constrict blood vessels. Drugs that do this are known as alpha blockers. High blood pressure (hypertension), if not treated, can result in kidney failure, stroke, and heart attack. The drug can also be used to relieve the obstruction of urine flow that can occur in men with an enlarged prostrate gland.