title: Prevalence of marijuana use does not differentially increase among youth after states pass medical marijuana laws: Commentary on and reanalysis of US National Survey on Drug Use in Households data 2002-2011.
abstract: There is considerable interest in the effects of medical marijuana laws (MML) on marijuana use in the USA, particularly among youth. The article by Stolzenberg et al. (2015) "The effect of medical cannabis laws on juvenile cannabis use" concludes that "implementation of medical cannabis laws increase juvenile cannabis use". This result is opposite to the findings of other studies that analysed the same US National Survey on Drug Use in Households data as well as opposite to studies analysing other national data which show no increase or even a decrease in youth marijuana use after the passage of MML. We provide a replication of the Stolzenberg et al. results and demonstrate how the comparison they are making is actually driven by differences between states with and without MML rather than being driven by pre and post-MML changes within states. We show that Stolzenberg et al. do not properly control for the fact that states that pass MML during 2002-2011 tend to already have higher past-month marijuana use before passing the MML in the first place. We further show that when within-state changes are properly considered and pre-MML prevalence is properly controlled, there is no evidence of a differential increase in past-month marijuana use in youth that can be attributed to state MML.
authors.affiliation: 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. Electronic address: mmwall@columbia.edu.
authors.forename: Melanie M
authors.initials: MM
authors.lastname: Wall
authors.affiliation: Department of Biostatistics, Mailman School of Public Health, Columbia University, New York NY, USA.
authors.forename: Christine
authors.initials: C
authors.lastname: Mauro
authors.affiliation: 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.
authors.forename: Deborah S
authors.initials: DS
authors.lastname: Hasin
authors.affiliation: Department of Epidemiology, Mailman School of Public Health, Columbia University, New York NY, USA.
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Keyes
authors.affiliation: Department of Emergency Medicine, University of California Davis, Sacramento Ca, USA.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Cerda
authors.affiliation: Department of Epidemiology, Mailman School of Public Health, Columbia University, New York NY, USA.
authors.forename: Silvia S
authors.initials: SS
authors.lastname: Martins
authors.affiliation: Research Foundation of Mental Hygiene, New York, NY, USA.
authors.forename: Tianshu
authors.initials: T
authors.lastname: Feng
mesh_terms: D000293:Adolescent; D002188:Cannabis; D006801:Humans; D008385:Marijuana Smoking / Q000331:legislation & jurisprudence; D064086:Medical Marijuana; D015995:Prevalence; D011795:Surveys and Questionnaires; D014481:United States
chemical_list: D064086:Medical Marijuana
keywords: Medical marijuana laws; Observational data analysis; Pre–post tests