Marijuana habit not linked to lung cancer

When compared with cannabis smokers who also used tobacco, habitual pot smokers had no significant increase in cancer risk.

In an analysis of marijuana smokers that excluded tobacco smokers, there were no significant differences in any of the comparisons, including habitual vs. nonhabitual use; number of joints smoked per day; duration of up to 20 years or duration of more than 20 years.

Other literature has shown a link between cannabis smoking and lung cancer, pulmonologist Michael Alberts said in an interview. However, he said, "The conventional wisdom is that cannabis smoking is not as dangerous as cigarette smoking."

The difference in risk is likely related to chemical additives in commercial cigarettes that aren’t present in most methods of inhaling marijuana smoke. 

http://www.clinicalpsychiatrynews.com/news/pain-and-addiction/single-article/marijuana-habit-not-linked-to-lung-cancer/73840afd2cca226b9e6a9ddc7cb0d039.html