Damage to Lungs

Although the evidence is inconclusive, it seems reasonable to assume that marijuana smoke may be as damaging to the lungs as tobacco smoke. Indeed, some studies have indicated that marijuana smoke contains more carcinogens than the smoke of tobacco cigarettes, and there is some concern that smoking marijuana could be related to lung cancer.
    The key factor here, however, may have more to do with quantity than anything else. While any smoke is bad for the human lungs, experts on lung cancer estimate that the level at which cigarettes made from tobacco produce definite changes in the cells of the human lungs is, on average, about twenty years of pack-a-day smoking. If marijuana is roughly equivalent to cigarettes in terms of carcinogenic danger—or even if it is two or three times as dangerous, as some authorities believe—then only extremely heavy marijuana smokers have any real cause to worry.