title: Effects of state medical marijuana laws on adolescent marijuana use.
abstract: OBJECTIVE
  Medical marijuana laws (MMLs) have been suggested as a possible cause of increases in marijuana use among adolescents in the United States. We evaluated the effects of MMLs on adolescent marijuana use from 2003 through 2011.
  
  
  METHODS
  We used data from the Youth Risk Behavior Survey and a difference-in-differences design to evaluate the effects of passage of state MMLs on adolescent marijuana use. The states examined (Montana, Rhode Island, Michigan, and Delaware) had passed MMLs at different times over a period of 8 years, ensuring that contemporaneous history was not a design confound.
  
  
  RESULTS
  In 40 planned comparisons of adolescents exposed and not exposed to MMLs across states and over time, only 2 significant effects were found, an outcome expected according to chance alone. Further examination of the (nonsignificant) estimates revealed no discernible pattern suggesting an effect on either self-reported prevalence or frequency of marijuana use.
  
  
  CONCLUSIONS
  Our results suggest that, in the states assessed here, MMLs have not measurably affected adolescent marijuana use in the first few years after their enactment. Longer-term results, after MMLs are more fully implemented, might be different.
authors.affiliation: Department of Health Outcomes and Policy and the Institute for Child Health Policy, University of Florida College of Medicine, Gainesville, FL, USA. sarah.landsman@ufl.edu
authors.forename: Sarah D
authors.initials: SD
authors.lastname: Lynne-Landsman
authors.forename: Melvin D
authors.initials: MD
authors.lastname: Livingston
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Wagenaar
mesh_terms: D000293:Adolescent; D003132:Commerce / Q000331:legislation & jurisprudence*; D003691:Delaware / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000453:epidemiology*; D008385:Marijuana Smoking / Q000453:epidemiology / Q000331:legislation & jurisprudence*; D008824:Michigan / Q000453:epidemiology; D009009:Montana / Q000453:epidemiology; D008517:Phytotherapy / Q000009:adverse effects*; D015995:Prevalence; D012237:Rhode Island / Q000453:epidemiology; D012307:Risk Factors; D013219:State Government