title: A review of co-morbid tobacco and cannabis use disorders: possible mechanisms to explain high rates of co-use.
abstract: BACKGROUND
  Tobacco and cannabis are among the most commonly used psychoactive substances worldwide, and are often used in combination. Evidence suggests that tobacco use contributes to an increased likelihood of becoming cannabis dependent and similarly cannabis use promotes transition to more intensive tobacco use. Further, tobacco use threatens cannabis cessation attempts leading to increased and accelerated relapse rates among cigarette smokers. Given that treatment outcomes are far from satisfactory among individuals engaged in both tobacco and cannabis use highlights the need for further exploration of this highly prevalent co-morbidity.
  
  
  OBJECTIVE
  Therefore, this review will elucidate putative neurobiological mechanisms responsible for facilitating the link between co-morbid tobacco and cannabis use.
  
  
  METHODS
  We performed an extensive literature search identifying published studies that examined co-morbid tobacco and cannabis use.
  
  
  RESULTS
  Evidence of both synergistic and compensatory effects of co-morbid tobacco and cannabis use have been identified. Following, co-morbid use of these substances will be discussed within the context of two popular theories of addiction: the addiction vulnerability hypothesis and the gateway hypothesis. Lastly, common route of administration is proposed as a facilitator for co-morbid use.
  While, only a paucity of treatment studies addressing co-morbid tobacco and cannabis use have been conducted, emerging evidence suggests that simultaneously quitting both tobacco and cannabis may yield benefits at both the psychological and neurobiological level. More research is needed to confirm this intervention strategy and future studies should consider employing prospective systematic designs.
authors: Institute of Medical Science (IMS), Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.|Schizophrenia Division, Centre for Addiction and Mental Health (CAMH), Toronto, Ontario, Canada.
authors: Rachel Allison
authors: RA
authors: Rabin
authors: Institute of Medical Science (IMS), Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.|Schizophrenia Division, Centre for Addiction and Mental Health (CAMH), Toronto, Ontario, Canada.|Division of Brain and Therapeutics, Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada.
authors: Tony Peter
authors: TP
authors: George
mesh_terms: D016739:Behavior, Addictive / Q000523:psychology; D015897:Comorbidity; D006801:Humans; D002189:Marijuana Abuse / Q000453:epidemiology* / Q000523:psychology; D011446:Prospective Studies; D011582:Psychological Theory; D014029:Tobacco Use Disorder / Q000453:epidemiology* / Q000523:psychology; D016896:Treatment Outcome