So if you burn a tobacco leaf it creates tar but if you burn a hemp leaf, there is no tar?
I heard a doctor on the radio years ago state that the carbon particles in pot smoke are much larger than those from cigarettes. The cilia in your lungs can collect those particles into phlegm and you cough it up. The smaller particles in cigs wedge between the cilia and it can’t move them. That’s why you just don’t see lung cancer among pot smokers at the levels you do in cigarette smokers. I don’t know if there are studies to back him up but it makes sense to me.
Similar components in tobacco and MJ smoke...THC may have some protective effects against lung cancer, but in any case there is the inhaled particle effect aka Black Lung.
http://www.webmd.com/cancer/news/20051017/pot-smoke-less-carcinogenic-than-tobacco
and
https://www.sciencedaily.com/releases/2007/12/071217110328.htm