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Cannabis Exposure and Lung Health

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Cannabis smoke and tobacco smoke are not equally carcinogenic

Unlike tobacco smoke exposure, cannabis smoke exposure - even long-term - is not positively associated with cancers of the lung or upper aerodigestive tract

  • "Despite the presence of carcinogens in marijuana smoke in concentrations comparable with those that are found in tobacco smoke, the weight of evidence from well-designed epidemiologic studies does not support the concept that habitual marijuana use in the manner and quantity in which it is customarily smoked, when adjusted for tobacco, is a significant risk factor for the development of lung cancer."
  • "There is moderate evidence of no statistical association between cannabis use and incidence of lung cancer [or] incidence of head and neck cancer."
  • "To investigate the association between cannabis smoking and lung cancer risk, data on 2,159 lung cancer cases and 2,985 controls were pooled from 6 case-control studies in the US, Canada, UK, and New Zealand within the International Lung Cancer Consortium. ... Compared to non-habitual or never users, the summary OR was 0.88 for individuals who smoked 1 or more joint-equivalents of cannabis per day and 0.94 for those consumed at least 10 joint-years. ... Results from our pooled analyses provide little evidence for an increased risk of lung cancer among habitual or long-term cannabis smokers."
  • "We conducted a population-based case-control study of the association between marijuana use and the risk of lung and upper aerodigestive tract cancers in Los Angeles. ... Although using marijuana for > or =30 joint-years was positively associated in the crude analyses with each cancer type (except pharyngeal cancer), no positive associations were observed when adjusting for several confounders including cigarette smoking. ... Our results ... suggest that the association of these cancers with marijuana, even long-term or heavy use, is not strong and may be below practically detectable limits."
  • "We hypothesized that there would be a positive association between marijuana use and lung cancer, and that the association would be more positive with heavier use. What we found instead was no association at all, and even a suggestion of some protective effect."
  • "The purpose of this retrospective cohort study was to examine the relationship of marijuana use to cancer incidence. The study population consisted of 64,855 examinees in the Kaiser Permanente multiphasic health checkup in San Francisco and Oakland (California, United States), between 1979-85. ... Follow-up for cancer incidence was conducted through 1993 (mean length 8.6 years). Compared with nonusers/experimenters (lifetime use of less than seven times), ever- and current use of marijuana were not associated with increased risk of cancer of all sites in analyses adjusted for sociodemographic factors, cigarette smoking, and alcohol use. Marijuana use also was not associated with tobacco-related cancers or with cancer of the following sites: colorectal, lung, melanoma, prostate, breast, cervix. ... We conclude that, in this relatively young study cohort, marijuana use and cancer were not associated in overall analyses."

Cannabis smoke exposure, even long-term, is not associated with the sort of significant adverse pulmonary effects associated with tobacco - such as COPD.

  • "Although regular smoking of marijuana is associated with an increased risk of symptoms of chronic bronchitis and evidence of inflammation and injury involving the larger airways, lung function findings, although mixed, do not provide compelling evidence that habitual marijuana smoking in the manner and amount that it is generally smoked increases the risk of COPD, at least at the population level."
  • "Neither current nor former marijuana use was associated with increased risk of cough, wheeze, or chronic bronchitis when compared to never marijuana users. ... Current and former marijuana smokers had significantly higher FEV1 (forced expiratory volume) ... when compared to never users. ... Both current and former marijuana use was associated with significantly less quantitative emphysema ... when compared to never users, even after adjusting for age, ... current tobacco smoking pack years, and BMI. ... In agreement with other published studies, we also did not find that marijuana use was associated with more obstructive lung disease. ... Among older adults with a history of tobacco use, marijuana use does not appear to increase risk for adverse lung function. ... There may be no to little increased risk of marijuana use for a further increase in respiratory symptoms or adverse effects ... among those with a history of concomitant tobacco use."

Vaporization -- which heats marijuana to a point where cannabinoid vapors form - mitigates consumers exposure to potential respiratory hazards, such as the inhalation of combustive smoke or exposure to unwanted particulate matter