The findings, published June 20 in the International Journal of Cancer, showed no link between marijuana smoking and cancer risk.
“Results from our pooled analyses provide little evidence for an increased risk of lung cancer among habitual or long-term cannabis smokers,” concluded the team, which included members from the International Lung Cancer Consortium.
Even when data was analyzed based on intensity, duration, consumption and age of initiation, no significant association was found.
The findings, the group adds, are consistent with a 2006 review that also showed no link between marijuana and lung cancer after adjusting for tobacco use.
Despite the fact that marijuana users don’t appear to be at greater risk of lung cancer, studies show that marijuana smoke does contain carcinogens. In fact, a marijuana ‘joint’ deposits four times as much tar in the lungs as an equivalent tobacco cigarette.
Hal Morgenstern, PhD, a University of Michigan epidemiologist and co-author of the latest study, suggests it might be that most marijuana users don’t smoke enough of it to get sick.
“When you think about people smoking 20-40 cigarettes a day for 40 years, they’re smoking hundreds of thousands of cigarettes. The exposure that marijuana users get… is more than a magnitude of difference less.”
On the other hand, cannabis smokers are known to inhale deeper and hold smoke in their lungs for longer than cigarette smokers do.
Others who have studied the link between marijuana and lung cancer, such as Donald P. Tashkin, MD, a lung specialist from the University of California, point to an often overlooked difference between marijuana and tobacco — certain compounds in marijuana have been shown to have anti-cancer effects.
This may be the reason why marijuana smokers are unlikely to develop lung cancer, he explains.
“The THC in marijuana has well-defined anti-tumoral effects that have been shown to inhibit the growth of a variety of cancers in animal models and tissue culture systems, thus counteracting the potentially tumorigenic effects of the procarcinogens in marijuana smoke.”
Similarly, one of Dr. Tashkin’s own studies, published in 2006, found that while heavy tobacco smokers experienced up to a 20-fold increase in lung cancer risk, even the most frequent users of cannabis were no more likely to develop lung cancer than the average person.
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