Intervention Efficacy in Trials Targeting Cannabis Use Disorders in Patients with Comorbid Psychosis

Introduction: Cannabis use disorders are highly prevalent in patients with schizophrenia and other psychoses, and are probably associated with a range of poor outcomes. Several trials have been conducted on this population, the results of which have been summarized in several systematic reviews but never in meta-analyses specifically regarding cannabis use. Methods: PubMed, PsycINFO, EMBASE, and The Cochrane Central Register of Controlled Trials were searched using predefined search terms. We included randomized trials of all types of interventions targeting cannabis use disorders in patients with schizophrenia spectrum disorders. We extracted information on intervention types, efficacy, trial characteristics, and risk of bias. Results: There was no evidence of an effect on frequency of cannabis use, but intervention effects of motivational intervention with or without cognitive behavior therapy were observed on quantity of use and on positive symptoms of schizophrenia. Psychosocial intervention did not have an appreciable effect on negative symptoms. Longer interventions appear to be more efficacious, and efficacy may be better in trials with comparatively few women. Larger trials may be better at establishing effects on positive symptoms. Conclusion: Psychosocial interventions appear moderately efficacious in reducing quantity of cannabis-use and positive symptoms.