Prazosin is in a group of drugs called alpha-adrenergic (AL-fa ad-ren-ER-jik) blockers. Prazosin relaxes your veins and arteries so that blood can more easily pass through them.
Prazosin is used to treat hypertension (high blood pressure).
Dizziness or lightheadedness, especially when getting up from a lying or sitting position
Loss of bladder control
swelling of the feet or lower legs
Incidence not known
Painful or prolonged erection of the penis
(prazosin hydrochloride) capsule