title: Associations between cigarette smoking and cannabis dependence: a longitudinal study of young cannabis users in the United Kingdom.
abstract: OBJECTIVE
  To determine the degree to which cigarette smoking predicts levels of cannabis dependence above and beyond cannabis use itself, concurrently and in an exploratory four-year follow-up, and to investigate whether cigarette smoking mediates the relationship between cannabis use and cannabis dependence.
  
  
  METHODS
  The study was cross sectional with an exploratory follow-up in the participants' own homes or via telephone interviews in the United Kingdom. Participants were 298 cannabis and tobacco users aged between 16 and 23; follow-up consisted of 65 cannabis and tobacco users. The primary outcome variable was cannabis dependence as measured by the Severity of Dependence Scale (SDS). Cannabis and tobacco smoking were assessed through a self-reported drug history.
  
  
  RESULTS
  Regression analyses at baseline showed cigarette smoking (frequency of cigarette smoking: B=0.029, 95% CI=0.01, 0.05; years of cigarette smoking: B=0.159, 95% CI=0.05, 0.27) accounted for 29% of the variance in cannabis dependence when controlling for frequency of cannabis use. At follow-up, only baseline cannabis dependence predicted follow-up cannabis dependence (B=0.274, 95% CI=0.05, 0.53). At baseline, cigarette smoking mediated the relationship between frequency of cannabis use and dependence (B=0.0168, 95% CI=0.008, 0.288) even when controlling for possible confounding variables (B=0.0153, 95% CI=0.007, 0.027).
  
  
  CONCLUSIONS
  Cigarette smoking is related to concurrent cannabis dependence independently of cannabis use frequency. Cigarette smoking also mediates the relationship between cannabis use and cannabis dependence suggesting tobacco is a partial driver of cannabis dependence in young people who use cannabis and tobacco.
authors.affiliation: Clinical Psychopharmacology Unit, University College London, Gower Street, London WC1E 6BT, United Kingdom. Electronic address: c.hindocha@ucl.ac.uk.
authors.forename: Chandni
authors.initials: C
authors.lastname: Hindocha
authors.affiliation: Clinical Psychopharmacology Unit, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Natacha D C
authors.initials: ND
authors.lastname: Shaban
authors.affiliation: Clinical Psychopharmacology Unit, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Tom P
authors.initials: TP
authors.lastname: Freeman
authors.affiliation: Clinical Psychopharmacology Unit, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Ravi K
authors.initials: RK
authors.lastname: Das
authors.affiliation: Clinical Psychopharmacology Unit, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Grace
authors.initials: G
authors.lastname: Gale
authors.affiliation: Clinical Psychopharmacology Unit, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Grainne
authors.initials: G
authors.lastname: Schafer
authors.affiliation: Department of Clinical, Educational and Health Psychology, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: Caroline J
authors.initials: CJ
authors.lastname: Falconer
authors.affiliation: Clinical Psychopharmacology Unit, University College London, Gower Street, London WC1E 6BT, United Kingdom; Department of Psychology, University of Exeter, Washington Singer Building, Perry Road, Exeter EX4 4QG, United Kingdom.
authors.forename: Celia J A
authors.initials: CJ
authors.lastname: Morgan
authors.affiliation: Clinical Psychopharmacology Unit, University College London, Gower Street, London WC1E 6BT, United Kingdom.
authors.forename: H Valerie
authors.initials: HV
authors.lastname: Curran
mesh_terms: D000293:Adolescent; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D002189:Marijuana Abuse / Q000175:diagnosis* / Q000453:epidemiology* / Q000523:psychology; D012907:Smoking / Q000453:epidemiology* / Q000523:psychology; D006113:United Kingdom / Q000453:epidemiology; D055815:Young Adult
keywords: Addiction; Cannabis; Co-morbidity; Dependence; Longitudinal; Tobacco; United Kingdom