title: Associations of cannabis and cigarette use with depression and anxiety at age 18: findings from the Avon Longitudinal Study of Parents and Children.
abstract: BACKGROUND
  Substance use is associated with common mental health disorders, but the causal effect of specific substances is uncertain. We investigate whether adolescent cannabis and cigarette use is associated with incident depression and anxiety, while attempting to account for confounding and reverse causation.
  
  
  METHODS
  We used data from ALSPAC, a UK birth cohort study, to investigate associations between cannabis or cigarettes (measured at age 16) and depression or anxiety (measured at age 18), before and after adjustment for pre-birth, childhood and adolescent confounders. Our imputed sample size was 4561 participants.
  
  
  RESULTS
  Both cannabis (unadjusted OR 1.50, 95% CI 1.26, 1.80) and cigarette use (OR 1.37, 95% CI 1.16, 1.61) increased the odds of developing depression. Adjustment for pre-birth and childhood confounders partly attenuated these relationships though strong evidence of association persisted for cannabis use. There was weak evidence of association for cannabis (fully adjusted OR 1.30, 95% CI 0.98, 1.72) and insufficient evidence for association for cigarette use (fully adjusted OR = 0.97, 95% CI 0.75, 1.24) after mutually adjusting for each other, or for alcohol or other substance use. Neither cannabis nor cigarette use were associated with anxiety after adjustment for pre-birth and childhood confounders.
  
  
  CONCLUSIONS
  Whilst evidence of association between cannabis use and depression persisted after adjusting for pre-term and childhood confounders, our results highlight the difficulties in trying to estimate and interpret independent effects of cannabis and tobacco on psychopathology. Complementary methods are required to robustly examine effects of cannabis and tobacco on psychopathology.
authors: School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom; Medical Research Council Integrative Epidemiology Unit at the University of Bristol, Bristol, United Kingdom; United Kingdom Centre for Tobacco Control Studies, University of Bristol, Bristol, United Kingdom.
authors: Suzanne H
authors: SH
authors: Gage
authors: School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom.
authors: Matthew
authors: M
authors: Hickman
authors: School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom.
authors: Jon
authors: J
authors: Heron
authors: Medical Research Council Integrative Epidemiology Unit at the University of Bristol, Bristol, United Kingdom; United Kingdom Centre for Tobacco Control Studies, University of Bristol, Bristol, United Kingdom.
authors: Marcus R
authors: MR
authors: Munafò
authors: Mental Health Sciences Unit, University College London, London, United Kingdom.
authors: Glyn
authors: G
authors: Lewis
authors: School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom.
authors: John
authors: J
authors: Macleod
authors: School of Social and Community Medicine, University of Bristol, Bristol, United Kingdom; Medical Research Council Centre for Neuropsychiatric Genetics and Genomics, Cardiff University, Cardiff, United Kingdom.
authors: Stanley
authors: S
authors: Zammit
mesh_terms: D000293:Adolescent; D001007:Anxiety / Q000453:epidemiology / Q000209:etiology / Q000503:physiopathology*; D015331:Cohort Studies; D003863:Depression / Q000453:epidemiology / Q000209:etiology / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008385:Marijuana Smoking / Q000009:adverse effects*; D010290:Parents; D012907:Smoking / Q000009:adverse effects*