The long-term effects of inhaled marijuana on human airways and lung parenchyma are unknown. It will be years before we fully understand the range and severity of lung injury related to this exposure. Although the inhalation of marijuana is not new, growing acceptance and legalization in many parts of the world have led to its increased use (1). Like all novel exposures, new medical treatments, or new imaging modalities, there is initially unwarranted optimism regarding their benefits and positive effects while underappreciating the negative consequences. This was true regarding the effect of cigarette smoke on the lung. Prior to 1950, full-page ads in popular magazines featured physicians extolling the benefits of various cigarette brands (2). Those ads disappeared with the publication of research connecting exposure to cigarette smoke and lung cancer (3). It took further decades of research to better understand the negative effects of cigarette smoke on lung function and the related multicompartment lung injury.