title: Association between marijuana exposure and pulmonary function over 20 years.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  METHODS
  Forced expiratory volume in the first second of expiration (FEV(1)) 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 FEV(1) and FVC. In contrast, the association between marijuana exposure and pulmonary function was nonlinear (P < .001): at low levels of exposure, FEV(1) increased by 13 mL/joint-year (95% CI, 6.4 to 20; P < .001) and FVC by 20 mL/joint-year (95% CI, 12 to 27; P < .001), but at higher levels of exposure, these associations leveled or even reversed. The slope for FEV(1) was -2.2 mL/joint-year (95% CI, -4.6 to 0.3; P = .08) at more than 10 joint-years and -3.2 mL per marijuana smoking episode/mo (95% CI, -5.8 to -0.6; P = .02) at more than 20 episodes/mo. With very heavy marijuana use, the net association with FEV(1) was not significantly different from baseline, and the net association with FVC remained significantly greater than baseline (eg, at 20 joint-years, 76 mL [95% CI, 34 to 117]; P < .001).
  
  
  CONCLUSIONS
  Occasional and low cumulative marijuana use was not associated with adverse effects on pulmonary function.
authors.affiliation: Department of Epidemiology and Biostatistics, University of California, San Francisco, 185 Berry St, Ste 5700, San Francisco, CA 94107, USA. mpletcher@epi.ucsf.edu
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Pletcher
authors.forename: Eric
authors.initials: E
authors.lastname: Vittinghoff
authors.forename: Ravi
authors.initials: R
authors.lastname: Kalhan
authors.forename: Joshua
authors.initials: J
authors.lastname: Richman
authors.forename: Monika
authors.initials: M
authors.lastname: Safford
authors.forename: Stephen
authors.initials: S
authors.lastname: Sidney
authors.forename: Feng
authors.initials: F
authors.lastname: Lin
authors.forename: Stefan
authors.initials: S
authors.lastname: Kertesz
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008137:Longitudinal Studies; D008168:Lung / Q000503:physiopathology*; D008297:Male; D008385:Marijuana Smoking / Q000009:adverse effects*; D008875:Middle Aged; D012907:Smoking / Q000009:adverse effects; D014797:Vital Capacity; D055815:Young Adult