Terazosin is in a group of drugs called alpha-adrenergic (AL-fa ad-ren-ER-jik) blockers. Terazosin relaxes your veins and arteries so that blood can more easily pass through them. It also relaxes the muscles in the prostate and bladder neck, making it easier to urinate. Terazosin is used to treat hypertension (high blood pressure), or to improve urination in men with benign prostatic hyperplasia (enlarged prostate). Terazosin may also be used for other purposes not listed in this medication guide.