GungHoShmo

I've been running for two years and smoking for one. About five months go my new roomate introduced me to smoking before exercising. Since then, I run 6-7 days a week and smoke or have smoked before going on each run. I seem to have no adverse effects and actually seem to cramp less. My question is if smoking before running is preventing my progression as a runner. Such as my lungs ability to hold a larger volume of oxygen, as well as the overall aerobic condition of my muscles. I don't see myself quitting smoking weed, but am just wondering if smoking before running is just tricking me into thinking I'm a better runner. Any informed opinions welcomed.