@Squander:
Yes your right, and here it what I found on a quick search:
Prazosin (Minipress) is an oral medicine used to treat high blood pressure. Prazosin is a competitive alpha-1 adrenergic receptor blocker. By blocking alpha-1 receptors on muscle cesll that surround blood vessels, prazosin causes vasodilation (widening) of the blood vessels, and consequently decrease in blood pressure