Doxazosin Mesylate Oral tablet. DOXAZOSIN (dox AY zoe sin) is an antihypertensive. It works by relaxing the blood vessels. It is used to treat benign prostatic hyperplasia (BPH) in men and to treat high blood pressure in both men and women. Take this medicine by mouth with a glass of water. Follow the directions on the prescription label. Take your doses at regular intervals. Do not take your medicine more often than directed. Do not stop taking except on the advice of your doctor or health care professional. Talk to your pediatrician regarding the use of this medicine in children.