Alpha receptors are found on the muscle in the prostate gland. This gland is found only in men and lies at the top of the tube connecting the bladder to the outside (urethra). The prostate gland often enlarges with advancing age (benign prostatic hyperplasia) and presses on the urethra. This can cause symptoms such as difficulty passing urine. By blocking the alpha receptors in the prostate gland, terazosin causes the muscle in the prostate to relax. This allows urine to flow freely past the prostate and relieves the urinary symptoms of this condition. Alpha receptors are also found in the muscle in the walls of blood vessels. By blocking these receptors, terazosin causes the muscle to relax and allows the blood vessels to widen. This lets the blood pass more easily through the blood vessels and hence reduces blood pressure. Terazosin can therefore be used to treat high blood pressure.