About prazosinselective alpha-1 adrenergic blocker, a quinazoline derivative, antihypertensive.mechanism of action of prazosinthe drug exerts its antihypertensive action by acting as a selective alpha-1 antagonist. it dilates both arteries and veins, thus it reduces total peripheral resistance, reduce blood pressure, & reduce venous return and cardiac output. it decreases central sympathetic outflow. the drug also reduces the tone of the internal sphincter of the bladder thus decrease the resistance to urinary outflow in patients with benign prostatic hypertrophy. it decrease the tone of prostatic and bladder neck muscles and relaxes bladder trigone, prostate, and prostatic urethra- reduces dynamic obstruction, increases urinary flow rate, causing more complete emptying of bladder. the drug decreases ldl cholesterol & increases hdl cholesterol.