title: Cannabis psychosis: examining the evidence for a distinctive psychopathology in a systematic and narrative review.
abstract: BACKGROUND
  The term "cannabis psychosis" has become ubiquitous in the psychiatric literature. Few authors have described the precise psychopathology of this potentially distinct subtype of psychosis. Specifically, little attention has been paid to exploring whether cannabis psychosis is characterized by a psychopathology which is different from that of other types of psychosis.
  
  
  OBJECTIVE
  The purpose of this paper was to systematically review the literature for evidence of a specific constellation of symptoms which are consistently characteristic of cannabis psychosis within an inpatient psychiatric setting and to determine whether these combine to create a psychopathology which is distinct from that of other types of psychosis.
  
  
  METHODS
  Systematic review using Meta-analysis Of Observational Studies in Epidemiology (MOOSE) guidelines.
  
  
  RESULTS
  13 studies of the 439 identified met the inclusion criteria. Only eight studies had sufficient internal and external validity to allow comparison in a narrative format of the psychopathology present, compared with controls. Of these eight selected studies, seven reported at least one significant difference (p < .05) in the psychopathology of the cannabis group to the control group used as a comparator.
  
  
  CONCLUSIONS
  This study should be interpreted with great caution and conclusions should not be generalized. These findings do not suggest that "cannabis psychosis" does not exist, only that from a psychopathological perspective it may not be qualitatively any different from other forms of psychosis. Future research in this area needs to focus on clarifying the definition or description of "cannabis psychosis" and the use of standardized robust experimental and/or observational designs to eliminate heterogeneity that may lead to inconclusive results.
authors.affiliation: Centre for Addiction Research and Education (Scotland), Centre for Neurosciences, Ninewells Hospital and Medical School, Dundee, Scotland. a.baldacchino@dundee.ac.uk
authors.forename: Alexander
authors.initials: A
authors.lastname: Baldacchino
authors.forename: Zoe
authors.initials: Z
authors.lastname: Hughes
authors.forename: Michael
authors.initials: M
authors.lastname: Kehoe
authors.forename: Hannah
authors.initials: H
authors.lastname: Blair
authors.forename: Ying
authors.initials: Y
authors.lastname: Teh
authors.forename: Stacey
authors.initials: S
authors.lastname: Windeatt
authors.forename: Ilana B
authors.initials: IB
authors.lastname: Crome
mesh_terms: D013759:Dronabinol / Q000009:adverse effects*; D006213:Hallucinogens / Q000009:adverse effects*; D006801:Humans; D008385:Marijuana Smoking / Q000009:adverse effects*; D011605:Psychoses, Substance-Induced / Q000209:etiology*
chemical_list: D006213:Hallucinogens; D013759:Dronabinol