MARIJUANA AND CHRONIC OBSTRUCTIVE LUNG DISEASE: A POPULATION-BASED STUDY

Wan C. Tan, MB, Christine Lo, BSc, Aimee Jong, BSc, Li Xing, MSc,
Mark J. FitzGerald, MB, William M. Vollmer, PhD, Sonia A. Buist, MD
PhD, Don D. Sin, MD MPH for the Vancouver Burden of Obstructive Lung
Disease (BOLD) Research Group

From the iCapture Centre for Cardiovascular and Pulmonary Research
(Tan, Lo, Jong, Xing, Sin), St. Paul's Hospital and the University of
British Columbia, and the Vancouver General Hospital (FitzGerald),
Vancouver, BC; the Oregon Health and Sciences University (Vollmer)
and the Kaiser Permanente Center for Health Research (Buist), Portland, USA

Correspondence to: Dr. Wan C. Tan, University of British Columbia,
iCapture Centre for Cardiovascular and Pulmonary Research, St. Paul's
Hospital, 1081 Burrard St., Vancouver BC V6Z 1Y6; fax 604 806-8351;
wtan@mrl.ubc.ca

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 ug 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.