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. col of the BOLD study. The prevalence of COPD was assumed to be 15%. 15 We conducted sampling in 2 stages. First, we used random-digit dialling to identify and recruit a randomized sample of at least 1000 people. 16 Recruits were then invited to the clinic to complete standardized questionnaires administered by interviewers. Demographic details were collected, and participants were asked about their respiratory health and symptoms, smoking history, quality of life, use of health care services and cardiovascular comorbidities and other respiratory diseases. We also performed spirometric testing before and after administration of a bronchodilator. 15 We collected data from August 2005 to April 2006.We obtained approval to conduct the study from the University of British Columbia and the Providence Health Care Research Ethics Board.
Questionnaire on marijuana useTo obtain details about participants' marijuana use, we used a 7-item questionnaire (Appendix 1, available at www.cmaj.ca /cgi/content/full/180/8/814/DC2).
Spirometric testingWe used a portable spirometer (EasyOne, ndd Medical Technologies, Andover, USA) to collect data on forced expiratory volume in 1 second (FEV 1 ) and forced vital capacity (FVC). We performed the spirometric tests before and after administering 200 μg of salbutamol (also known as a...
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