The National Organization for the Reform of Marijuana Laws responds to a recent study linking heavy cannabis use to lung cancer. The study, reported in the European Respiratory Journal, generated headlines like these:
But as NORML's Paul Armentano points out, the researchers actually reported that "cannabis smoking (defined as lifetime use of ?20 joints) was not associated with a significantly increased risk of lung cancer." Only in the group with the highest exposure (more than 10.5 joint-years) was there a statistically significant increase in risk. The lung cancer risk in this group, which included just 16 subjects (14 out of 79 cases and two out of 324 controls), was about six times the risk among nonsmokers, compared to an overall risk ratio of about 7 to 1 for the cigarette smokers in the study. Armentano notes that the findng is at odds with the results of several other much larger epidemiological studies that failed to find clear evidence that smoking pot increases the risk of cancer. He takes a more detailed look at that research here.
As Armentano notes, there is some evidence that cannabinoids help counteract the effects of carcinogens, whereas nicotine may potentiate them. Still, it makes sense that inhaling enough combustion products from any burning organic matter for a long enough period of time could lead to lung cancer. It may just be that pot smokers, who typically smoke far less than cigarette smokers do, are not, by and large, getting a big enough dose. For relatively heavy consumers worried about a possible cancer risk, there are always vaporizers (which heat cannabis to release THC instead of burning it). And brownies.