Pulmonary Effects of Marijuana Inhalation

Megan L Howden; Matthew T Naughton


Expert Rev Resp Med. 2011;5(1):87-92. 

In This Article


Cannabis smoke contains up to twice as many polyaromatic hydrocarbons as tobacco smoke.[34] These are some of the many carcinogenic compounds found in marijuana smoke and this, along with the technique of marijuana smoking, suggests that there may be an associated risk of malignancy. Numerous case reports, cohort and case–control studies have examined the effect of marijuana smoking on the risk of malignancies. The results have been variable with some studies showing a strong association, others showing none, however, there are numerous potential confounding factors.[34–37] A systematic review in 2006 failed to clearly establish a link between marijuana smoking and lung cancer, although molecular, histological and cellular changes were identified in sputum, bronchial washings and endobronchial biopsies of marijuana smokers.[37] These changes were similar to those seen in tobacco smokers. A large case–control study in the same year, however, found no evidence of an association between marijuana smoking and lung or upper respiratory tract cancers.[38] A much smaller case–control study by Aldington et al. found that in heavy cannabis smokers the relative risk of lung cancer was increased to 5.7 (95% CI: 1.5–21.6).[34] This association was not found in subjects who had a history of smoking of less than 10.5 joint-years. The authors did, however, report an 8% increase in lung cancer risk with each joint-year, similar to the findings of tobacco smoking, although these statistics have been questioned.[39] A pooled analysis of three North African case–control studies also found a significant association between marijuana smoking and lung cancer (odds ratio: 2.3 after adjusting for tobacco smoking), however, the adjustment could not take into account the frequent practice in North Africa of mixing tobacco with cannabis and the amount of cannabis consumed was not reported. Thus, while the histological findings are suggestive of the malignant potential of marijuana, the clinical outcomes identified to date are not supportive of this link.


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