Association between marijuana exposure and pulmonary function over 20 years

Abstract

Context: Marijuana smoke contains many of the same constituents as tobacco smoke, but whether it has similar adverse effects on pulmonary function is unclear. Objective: To analyze associations between marijuana (both current and lifetime exposure) and pulmonary function. Design, Setting, and Participants: The Coronary Artery Risk Development in Young Adults (CARDIA) study, a longitudinal study collecting repeated measurements of pulmonary function and smoking over 20 years (March 26, 1985-August 19, 2006) in a cohort of 5115 men and women in 4 US cities. Mixed linear modeling was used to account for individual age-based trajectories of pulmonary function and other covariates including tobacco use, which was analyzed in parallel as a positive control. Lifetime exposure to marijuana joints was expressed in joint-years, with 1 joint-year of exposure equivalent to smoking 365 joints or filled pipe bowls. Main Outcome Measures: Forced expiratory volume in the first second of expiration (FEV1) and forced vital capacity (FVC). Results: Marijuana exposure was nearly as common as tobacco exposure but was mostly light (median, 2-3 episodes per month). Tobacco exposure, both current and lifetime, was linearly associated with lower FEV1 and FVC. In contrast, the association between marijuana exposure and pulmonary function was nonlinear (P