title: Past 15-year trends in adolescent marijuana use: Differences by race/ethnicity and sex.
abstract: BACKGROUND
  The potential for increases in adolescent marijuana use is an important concern given recent changes in marijuana policy. The purpose of this study was to estimate trends in marijuana use from 1999 to 2013 among a national sample of US high school students. We examine changes over time by race/ethnicity and sex.
  
  
  METHODS
  Data are from the National Youth Risk Behavior Survey (YRBS), which involves biennial, school-based surveys that generate nationally representative data about 9th-12th grade students in the United States. Students self-reported sex, race/ethnicity, and marijuana use (i.e., lifetime use, past 30-day use, any use before age 13). We generated national estimates of the prevalence of marijuana use for the time period, and also tested for linear and quadratic trends (n=115,379).
  
  
  RESULTS
  The prevalence of lifetime marijuana use decreased modestly from 1999 to 2009 (44% to 37%), and has increased slightly since 2009 (41%). Other marijuana use variables (e.g., past 30-day use) followed a similar pattern over time. The prevalence of past 30-day use from 1999 to 2013 for all groups and both sexes was 22.5%, and it was lowest among Asians and highest among American Indian/Alaska Natives. Although boys have historically had a higher prevalence of marijuana use, results indicate that male-female differences in marijuana use decreased over time.
  
  
  CONCLUSIONS
  Despite considerable changes in state marijuana policies over the past 15 years, marijuana use among high school students has largely declined. Continued surveillance is needed to assess the impact of policy changes on adolescent marijuana use.
authors.affiliation: Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, United States. Electronic address: rjohnson@jhu.edu.
authors.forename: Renee M
authors.initials: RM
authors.lastname: Johnson
authors.affiliation: Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, United States.
authors.forename: Brian
authors.initials: B
authors.lastname: Fairman
authors.affiliation: University of Southern California School of Social Work, Los Angeles, CA, United States.
authors.forename: Tamika
authors.initials: T
authors.lastname: Gilreath
authors.affiliation: Boston University School of Public Health, Boston, MA, United States.
authors.forename: Ziming
authors.initials: Z
authors.lastname: Xuan
authors.affiliation: Boston University School of Public Health, Boston, MA, United States.
authors.forename: Emily F
authors.initials: EF
authors.lastname: Rothman
authors.affiliation: Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, United States.
authors.forename: Taylor
authors.initials: T
authors.lastname: Parnham
authors.affiliation: Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, United States.
authors.forename: C Debra M
authors.initials: CD
authors.lastname: Furr-Holden
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior / Q000523:psychology*; D005006:Ethnicity / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D008385:Marijuana Smoking / Q000453:epidemiology* / Q000639:trends*; D015995:Prevalence; D044469:Racial Groups / Q000706:statistics & numerical data*; D012309:Risk-Taking; D012574:Schools; D012737:Sex Factors; D013334:Students / Q000523:psychology*; D019966:Substance-Related Disorders / Q000453:epidemiology; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology
keywords: Adolescent; Marijuana/cannabis; Race/ethnicity; Sex differences