I am an anti smoking activist. does smoking causes impotancy and how ?

Yes, it does: Smoking causes constriction of blood vessels, which in many people are already constricted secondary to arteriosclerosis, which both high cholesterol, hypertension and smoking also contribute to. Erectile dysfunction occurs mostly because of blood vessel problems, and the drugs used to treat it assist in opening up those blood vessels. Smoking causes decreased libido from hormone issues as well.