Studies of the drug phenoxybenzamine, a non-specific alpha blocker, led to a better understanding of the control of the smooth muscle tone of the prostate and the opening to the bladder, the bladder neck. Alpha blockers cause a relaxation of these structures and therefore permit urine to flow more freely out of the bladder and into the prostatic urethra.
In 1976, Pfizer introduced Minipress (prazosin HCL) in the

