Does cannabis use predispose to chronic airflow obstruction?

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-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 [4–7]. 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 [4–6, 8–10] and longitudinally [11–13]. 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].