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.