title: Adolescent marijuana use from 2002 to 2008: higher in states with medical marijuana laws, cause still unclear.
abstract: OBJECTIVE
  Since 1996, 16 states have legalized marijuana use for medical purposes. The current study provides a scientific assessment of the association of medical marijuana laws (MML) and adolescent marijuana use using national data.
  
  
  METHODS
  State representative survey data on approximately 23,000 12-17 year olds were collected by the National Survey on Drug Use and Health annually from 2002-2008. Yearly state-specific estimates of prevalence of past-month marijuana use and perception of its riskiness were statistically tested for differences between states with and without MML by year and across years.
  
  
  RESULTS
  States with MML had higher average adolescent marijuana use, 8.68% (95% CI: 7.95-9.42) and lower perception of riskiness, during the period 2002-2008 compared to states without MML, 6.94% (95% CI: 6.60-7.28%). In the eight states that passed MML since 2004, in the years prior to MML passage, there was already a higher prevalence of use and lower perceptions of risk in those states compared to states that have not passed MML.
  
  
  CONCLUSIONS
  While the most likely of several possible explanations for higher adolescent marijuana use and lower perceptions of risk in MML states cannot be determined from the current study, results clearly suggest the need for more empirically-based research on this topic.
authors.affiliation: Department of Biostatistics, Mailman School of Public Health, Columbia University, New York, NY 10032-3727, USA. mmwall@columbia.edu
authors.forename: Melanie M
authors.initials: MM
authors.lastname: Wall
authors.forename: Ernest
authors.initials: E
authors.lastname: Poh
authors.forename: Magdalena
authors.initials: M
authors.lastname: Cerdá
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Keyes
authors.forename: Sandro
authors.initials: S
authors.lastname: Galea
authors.forename: Deborah S
authors.initials: DS
authors.lastname: Hasin
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D001294:Attitude to Health; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D008385:Marijuana Smoking / Q000453:epidemiology* / Q000331:legislation & jurisprudence*; D011640:Public Policy; D012306:Risk; D013219:State Government; D014481:United States / Q000453:epidemiology