Prazosin is used for:

Treating high blood pressure and benign prostatic hyperplasia (BPH). It may also be used to treat other conditions as determined by your doctor.

Prazosin is an alpha-blocker. The exact way it works is unknown, but it is thought to block a chemical in the body, causing blood vessels and the muscles around the urethra to relax. This helps to lower blood pressure and to improve urinary symptoms associated with enlargement of the prostate (BPH)...