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.You should not use this medication if you are allergic to terazosin. Terazosin may cause dizziness or fainting, especially when you first start taking it or when you start taking it again.erazosin may also be used for other purposes not listed in this medication guide. You should not use this medication if you are allergic to terazosin. Terazosin may cause dizziness or fainting, especially when you first start taking it or when you start taking it again.