title: Trends in the co-occurrence of tobacco and cannabis use in 15-year-olds from 2002 to 2010 in 28 countries of Europe and North America.
abstract: BACKGROUND
  Cannabis and tobacco use frequently co-occur. Adolescents who consume both substances experience more respiratory distress and psychosocial problems and are less likely to stop compared with those who use either tobacco or cannabis alone. This study examined time trends in tobacco and cannabis use among 15-year-olds in Europe and North America between 2002 and 2010.
  
  
  METHODS
  Twenty-eight countries were included and merged into six regions based on their welfare systems. Adolescents (n = 142 796) were divided in four 'user groups': 'no-users', 'tobacco and cannabis users', 'tobacco-only users' and 'cannabis-only users'. Prevalence rates are reported by study-wave and region. Logistic regressions with study wave as independent variable were used to study trends in the user groups and regions. Interaction effects between time and gender were considered.
  
  
  RESULTS
  Overall, tobacco use, and concurrent tobacco and cannabis use decreased by 3 and 3.7%, respectively, but prevalence rates varied by region. Only in North America, an interaction effect between time and gender was found in tobacco and cannabis users.
  
  
  CONCLUSIONS
  Although this study demonstrates a decrease in tobacco and cannabis use in most regions, it also shows that the use of both substances is related. Therefore, studying the co-occurring use of tobacco and cannabis is necessary.
authors: 1 Department of Public Health, Ghent University, Ghent, Belgium Anne.Hublet@Ugent.be.
authors: Anne
authors: A
authors: Hublet
authors: 2 National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark.
authors: Pernille
authors: P
authors: Bendtsen
authors: 3 Interdisciplinary Social Sciences, Utrecht University, Utrecht, The Netherlands.
authors: Margreet E
authors: ME
authors: de Looze
authors: 4 Epidemiology Unit, University Mental Health Research Institute, Athens, Greece.
authors: Anastasios
authors: A
authors: Fotiou
authors: 5 School of Medicine, University of St Andrews, St Andrews, Scotland.
authors: Peter
authors: P
authors: Donnelly
authors: 6 Faculty of Nursing, University of Iceland, Reykjavik, Iceland.
authors: Runar
authors: R
authors: Vilhjalmsson
authors: 7 Jessenius Faculty of Medicine, Comenius University, Martin, Slovak Republic.
authors: Tibor
authors: T
authors: Baska
authors: 8 Chronic Disease Department, The National Institute for Health Development, Tallinn, Estonia.
authors: Katrin
authors: K
authors: Aasvee
authors: 9 Croatian National Institute of Public Health, Zagreb, Croatia.
authors: Iva P
authors: IP
authors: Franelic
authors: 10 Health Promotion Research Centre, National University of Ireland, Galway, Ireland.
authors: Saoirse
authors: S
authors: Nic Gabhainn
authors: 3 Interdisciplinary Social Sciences, Utrecht University, Utrecht, The Netherlands.
authors: Tom F M
authors: TF
authors: ter Bogt
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior; D005060:Europe; D005260:Female; D006306:Health Surveys; D006801:Humans; D008297:Male; D008385:Marijuana Smoking / Q000453:epidemiology* / Q000639:trends*; D009656:North America; D015995:Prevalence; D012907:Smoking / Q000453:epidemiology* / Q000639:trends*