title: Medical marijuana laws and adolescent marijuana use in the USA from 1991 to 2014: results from annual, repeated cross-sectional surveys.
abstract: BACKGROUND
  Adolescent use of marijuana is associated with adverse later effects, so the identification of factors underlying adolescent use is of substantial public health importance. The relationship between US state laws that permit marijuana for medical purposes and adolescent marijuana use has been controversial. Such laws could convey a message about marijuana acceptability that increases its use soon after passage, even if implementation is delayed or the law narrowly restricts its use. We used 24 years of national data from the USA to examine the relationship between state medical marijuana laws and adolescent use of marijuana.
  
  
  METHODS
  Using a multistage, random-sampling design with replacement, the Monitoring the Future study conducts annual national surveys of 8th, 10th, and 12th-grade students (modal ages 13-14, 15-16, and 17-18 years, respectively), in around 400 schools per year. Students complete self-administered questionnaires that include questions on marijuana use. We analysed data from 1 098 270 adolescents surveyed between 1991 and 2014. The primary outcome of this analysis was any marijuana use in the previous 30 days. We used multilevel regression modelling with adolescents nested within states to examine two questions. The first was whether marijuana use was higher overall in states that ever passed a medical marijuana law up to 2014. The second was whether the risk of marijuana use changed after passage of medical marijuana laws. Control covariates included individual, school, and state-level characteristics.
  
  
  RESULTS
  Marijuana use was more prevalent in states that passed a medical marijuana law any time up to 2014 than in other states (adjusted prevalence 15·87% vs 13·27%; adjusted odds ratio [OR] 1·27, 95% CI 1·07-1·51; p=0·0057). However, the risk of marijuana use in states before passing medical marijuana laws did not differ significantly from the risk after medical marijuana laws were passed (adjusted prevalence 16·25% vs 15·45%; adjusted OR 0·92, 95% CI 0·82-1·04; p=0·185). Results were generally robust across sensitivity analyses, including redefining marijuana use as any use in the previous year or frequency of use, and reanalysing medical marijuana laws for delayed effects or for variation in provisions for dispensaries.
  
  
  CONCLUSIONS
  Our findings, consistent with previous evidence, suggest that passage of state medical marijuana laws does not increase adolescent use of marijuana. However, overall, adolescent use is higher in states that ever passed such a law than in other states. State-level risk factors other than medical marijuana laws could contribute to both marijuana use and the passage of medical marijuana laws, and such factors warrant investigation.
  
  
  BACKGROUND
  US National Institute on Drug Abuse, Columbia University Mailman School of Public Health, New York State Psychiatric Institute.
authors: Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY, USA; Department of Psychiatry, Columbia University Medical Center, New York, NY, USA; New York State Psychiatric Institute, New York, NY, USA. Electronic address: deborah.hasin@gmail.com.
authors: Deborah S
authors: DS
authors: Hasin
authors: Department of Biostatistics, Mailman School of Public Health, Columbia University, New York, NY, USA; Department of Psychiatry, Columbia University Medical Center, New York, NY, USA; New York State Psychiatric Institute, New York, NY, USA.
authors: Melanie
authors: M
authors: Wall
authors: Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY, USA.
authors: Katherine M
authors: KM
authors: Keyes
authors: Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY, USA.
authors: Magdalena
authors: M
authors: Cerdá
authors: Department of Psychology, University of Michigan, Ann Arbor, MI, USA; Institute for Social Research, University of Michigan, Ann Arbor, MI, USA.
authors: John
authors: J
authors: Schulenberg
authors: Institute for Social Research, University of Michigan, Ann Arbor, MI, USA.
authors: Patrick M
authors: PM
authors: O'Malley
authors: Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY, USA.
authors: Sandro
authors: S
authors: Galea
authors: RAND Corporation, Santa Monica, CA, USA; National Bureau of Economic Research, Cambridge, MA, USA.
authors: Rosalie
authors: R
authors: Pacula
authors: Research Foundation of Mental Hygiene, New York, NY, USA.
authors: Tianshu
authors: T
authors: Feng
mesh_terms: D000293:Adolescent; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D002189:Marijuana Abuse / Q000453:epidemiology*; D008385:Marijuana Smoking / Q000453:epidemiology*; D064086:Medical Marijuana / Q000627:therapeutic use*; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology
chemical_list: D064086:Medical Marijuana