marijuana is actually less harmful than cigarettes. In chronic marijuana users, areas of the lungs are more pink and irritated. In addition, many areas that were once coated with cilia (hair) are somehow changed into skin that is identicle to that on the outside of your body. These dangers are more associated with smoking than anything else, and will likely have some increasing effect on the aftermath of tobacco smoking (less cilia=less filtration in your lungs), but people that use only marijuana and not tobacco have not been found to be at risk for cancer.

Now, I need a cigarette.