Oh, and as for the smoking part:
Smoking, in general, is bad. Though combustion carbon monoxide (CO) and tar are released.
CO permanently binds to the hemoglobin in your red blood cells, thus forever hindering the transportation of oxygen by the affected red cells. Red cells have a life of 120 days, so only after 120 days of not smoking will a maximum of oxygen transportation reoccur in your body.
Tar is a substance produced by combustion of aromatic esters. It is extremely toxic to all cells and will affect your respiratory system, producing bronchitis, emphysema and many other horrible conditions.
Smoking will slowly paralyze the cilia of the trachea/windpipe (this is still reversible), thus making your lungs more vulnerable to bacteria, microorganisms, ash, dust or any other airborne particle.
All of these will sustain the build-up of precancerous formations in the lungs and body, thus leading to cancer.
Yet:
There are many studies out there that suggest that smoking cannabis, even in amazingly large quantities (70 joints a day!) will not affect the lungs and body at all, in regards to cancer formation. At all. Actually, if you want to be blunt (hihi...) about it, a 1974 Virginia University study showed that cannabis succesfully hinders the formation of breast, lung and skin cancer. A study performed in Madrid in 2000 proved that cannabis will stop the growth of tumors in the brain. I could go on and on, but I'd rather that you check these out for yourself:
https://www.rollitup.org/general-marijuana-growing/151533-medical-marijuana-uses-700-medical.html
And if you still want to completely eliminate CO and tar, buy a vaporizer.