Marijuana and chronic obstructive lung disease: a population-based study

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Abstract

Background: Our aim was to determine the combined and independent effects of tobacco and marijuana smoking on respiratory symptoms and chronic obstructive pulmonary disease (COPD) in the general population.

Method: We surveyed a random sample of 878 people aged 40 years or older living in Vancouver, Canada, about their respiratory history and their history of tobacco and marijuana smoking. We performed spirometric testing before and after administration of 200 µg of salbutamol. We examined the association between tobacco and marijuana smoking and COPD.

Results: The prevalence of a history of smoking in this sample was 45.5% (95% confidence interval [CI] 42.2%-48.8%) for marijuana use and 53.1% (95% CI 49.8%-56.4%) for tobacco use. The prevalence of current smoking (in the past 12 months) was 14% for marijuana use and 14% for tobacco use. Compared with nonsmokers, participants who reported smoking only tobacco, but not those who reported smoking only marijuana, experienced more frequent respiratory symptoms (odds ratio [OR] 1.50, 95% CI 1.05-2.14) and were more likely to have COPD (OR 2.74, 95% CI 1.66-4.52). Concurrent use of marijuana and tobacco was associated with increased risk (adjusted for age, asthma and comorbidities) of respiratory symptoms (OR 2.39, 95% CI 1.58-3.62) and COPD (OR 2.90, 95% CI 1.53-5.51) if the lifetime dose of marijuana exceeded 50 marijuana cigarettes. The risks of respiratory symptoms and of COPD were related to a synergistic interaction between marijuana and tobacco.

Interpretation: Smoking both tobacco and marijuana synergistically increased the risk of respiratory symptoms and COPD. Smoking only marijuana was not associated with an increased risk of respiratory symptoms or COPD.

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CMAJ 2009;180(8):814-20

Cannabis, commonly known as marijuana, is the most widely used illegal drug in the world. After tobacco, it is the second most widely smoked substance in the general population, with a conservatively estimated 11 million users in the United States and 160 million users worldwide. 1,2 The majority of people in both developed and developing countries who currently smoke tobacco have also smoked marijuana.3-6

Concerns about the impact of marijuana on lung health are based on the fact that both the gaseous and the particulate phases of tobacco and cannabis smoke contain a similar range of harmful...