Does cannabis use predispose to chronic airflow obstruction?

Abstract

C annabis (derived from the ubiquitous plant, Cannabis sativa, and also known as marijuana) is the most widely used illicit drug worldwide, as well as the second most commonly smoked substance after tobacco, with an estimated 166 million users (3.9% of 15-64 yr olds) [1]. Its wide popularity is due to the euphoric effects of its major psychoactive ingredient, D 9-tetrahydrocannabinol (THC). Since the gas and particulate phase constituents of the smoke of marijuana are at least qualitatively similar to those of tobacco, the major exception being the nicotine in tobacco and the ,60 cannabinoid (THC-like) components in marijuana [2,3], there has long been concern that regular smoking of marijuana might increase the risk of developing chronic airflow obstruction and chronic obstructive pulmonary disease (COPD), by analogy with the well-known detrimental effects of tobacco. Several studies have documented that smokers of marijuana, even in the absence of tobacco smoking, show a higher prevalence of symptoms of chronic bronchitis than nonsmokers [4][5][6][7]. However, the association between marijuana smoking and airflow obstruction is less clear. Several groups of investigators have addressed the latter question by measuring lung function in convenience samples or stratified random population samples of users and nonusers of marijuana and/ or tobacco both cross-sectionally [4][5][6][8][9][10] and longitudinally [11][12][13]. The most recent study of the possible association of marijuana use with lung function abnormality appears in this issue of the European Respiratory Journal [14].Previously published studies have yielded conflicting results relating to marijuana use and lung function. An early crosssectional study of 74 young (mean age 24 yrs) habitual marijuana smokers showed no differences in either spirometric indices or sensitive measures of small airways function (closing volume or percentage change in nitrogen concentration between 750 and 1,250 mL of expired volume (DN 2 750-1250)) among marijuana users compared with non-marijuana smoking controls matched on age and tobacco smoking [8]. Interestingly, however, the 50 non-tobacco-smoking marijuana smokers (MSs) exhibited airway resistances (Raw) that were modestly (28%) but significantly (p,0.001) higher than Raw among both nonsmoker (NS) and tobacco smoker (TS) controls; similar differences were noted for specific airway conductance (sGaw). These findings suggested that marijuana smoking may cause mild, but significant, narrowing of larger airways not detectable in similarly aged tobacco smokers, but no demonstrable abnormality involving the smaller airways. A later cross-sectional study by the same authors in a Los Angeles convenience sample of young (mean age 34 yrs) heavy MSs (n5144), smokers of both marijuana and tobacco (MTSs; n5135), TSs (n579) and NSs (n597) showed similar results [4], i.e. no abnormalities in spirometric or small airways indices (closing volume, DN 2 750-1250 or measures derived from flowvolume curves obtained with air and a helium-...

Association Between Marijuana Exposure and Pulmonary Function Over 20 Years

“…Lower FEV1/FVC in marijuana smokers, however, can be explained at least partly by a tendency towards higher FVC or total lung capacity 28,29,32 . A recent longitudinal study, which demonstrated significantly higher FVC and total lung capacity with marijuana exposure, strongly supports this notion 13,20 , as does our study.…”

“…Prior studies of marijuana and pulmonary function have yielded apparently conflicting results 10–13 . Many studies have focused on the ratio of FEV1/FVC, lower values of which suggest the presence of airway obstruction, and have found either no association 10,20,27 or lower FEV1/FVC with marijuana use 28–32 .…”

“…To explain the higher FVC previously observed in marijuana smokers 20,32 , some have proposed that the deep inspiratory maneuvers practiced by marijuana smokers could stretch the lungs 13,20 , resulting in larger lung volumes 20,32 . Another speculative possibility is strengthening of chest wall musculature or another “training” effect that allows marijuana users to inspire more fully (closer to total lung capacity) on spirometry testing.…”

“…Prior studies of marijuana smokers have demonstrated consistent evidence of airway mucosal injury and inflammation 7–9 , and increased respiratory symptoms such as cough, phlegm production and wheeze similar to tobacco smokers 10–12 . However, analyses of pulmonary function and lung disease have failed to detect clear adverse effects of marijuana use on pulmonary function 10–13 . It is possible that cumulative damage to the lungs from years of marijuana use could be masked by short-term effects; prior analyses have not attempted to disentangle these factors.…”

Cannabis, tobacco smoking, and lung function: a cross-sectional observational study in a general practice population

“…In contrast, previous studies have not always found strong or consistent evidence that cannabis smoking has adverse effects on objective measures of COPD such as the FEV1/FVC ratio. 24,25 The present study did find evidence of such effects, over and above those that appeared attributable to the tobacco use of cannabis smokers. It has been suggested that discrepancies in the evidence partly relate to the extent that cannabis use is associated with increased FVC (which may result from repeated pulmonary hyperinflation related to the way cannabis is smoked.…”