This study, co-authored by Donald Tashkin of UCLA, one of the world’s leading experts on the effects of marijuana on the lungs, compared 1,212 cancer patients with 1,040 cancer-free controls matched for age, gender and neighborhood in order to see if there was a relation between marijuana use and cancers of the lungs, throat and mouth (cancers commonly caused by cigarette smoking). After adjusting for cigarette smoking, researchers found no indication that marijuana smokers had an increased cancer risk. Indeed there was a trend, albeit not statistically significant, toward a reduced cancer risk among marijuana smokers as compared to those who did not use marijuana, leading the researchers to speculate that marijuana might have a “protective effect.”

M. Hashibe et al., “Marijuana use and the risk of lung and upper aerodigestive tract cancers: results of a population-based case-control study,” Cancer Epidemiology Biomarkers & Prevention 15, no. 10 (October 2006): 1829-1834.

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