• Katy Cooper, Robin Chatters, Eva Kaltenthaler, and Ruth Wong.
• Health Economics and Decision Science, School of Health and Related Research, University of Sheffield, Sheffield, UK.
• Health Technol Assess. 2015 Jul 1; 19 (56): 1-130.

BackgroundCannabis is the most commonly used illicit drug worldwide. Cannabis dependence is a recognised psychiatric diagnosis, often diagnosed via the Diagnostic and Statistical Manual of Mental Disorders criteria and the International Classification of Diseases, 10th Revision. Cannabis use is associated with an increased risk of medical and psychological problems. This systematic review evaluates the use of a wide variety of psychological and psychosocial interventions, such as motivational interviewing (MI), cognitive-behavioural therapy (CBT) and contingency management.ObjectiveTo systematically review the clinical effectiveness of psychological and psychosocial interventions for cannabis cessation in adults who use cannabis regularly.Data SourcesStudies were identified via searches of 11 databases [MEDLINE, EMBASE, Cochrane Controlled Trials Register, Health Technology Assessment (HTA) database, Database of Abstracts of Reviews of Effects, Cochrane Database of Systematic Reviews, NHS Economic Evaluation Database, PsycINFO, Web of Science Conference Proceedings Citation Index, ClinicalTrials.gov and metaRegister of Current Controlled Trials] from inception to February 2014, searching of existing reviews and reference tracking.MethodsRandomised controlled trials (RCTs) assessing psychological or psychosocial interventions in a community setting were eligible. Risk of bias was assessed using adapted Cochrane criteria and narrative synthesis was undertaken. Outcomes included change in cannabis use, severity of cannabis dependence, motivation to change and intervention adherence.ResultsThe review included 33 RCTs conducted in various countries (mostly the USA and Australia). General population studies: 26 studies assessed the general population of cannabis users. Across six studies, CBT (4-14 sessions) significantly improved outcomes (cannabis use, severity of dependence, cannabis problems) compared with wait list post treatment, maintained at 9 months in the one study with later follow-up. Studies of briefer MI or motivational enhancement therapy (MET) (one or two sessions) gave mixed results, with some improvements over wait list, while some comparisons were not significant. Four studies comparing CBT (6-14 sessions) with MI/MET (1-4 sessions) also gave mixed results: longer courses of CBT provided some improvements over MI. In one small study, supportive-expressive dynamic psychotherapy (16 sessions) gave significant improvements over one-session MI. Courses of other types of therapy (social support group, case management) gave similar improvements to CBT based on limited data. Limited data indicated that telephone- or internet-based interventions might be effective. Contingency management (vouchers for abstinence) gave promising results in the short term; however, at later follow-ups, vouchers in combination with CBT gave better results than vouchers or CBT alone. Psychiatric population studies: seven studies assessed psychiatric populations (schizophrenia, psychosis, bipolar disorder or major depression). CBT appeared to have little effect over treatment as usual (TAU) based on four small studies with design limitations (both groups received TAU and patients were referred). Other studies reported no significant difference between types of 10-session therapy.LimitationsIncluded studies were heterogeneous, covering a wide range of interventions, comparators, populations and outcomes. The majority were considered at high risk of bias. Effect sizes were reported in different formats across studies and outcomes.ConclusionsBased on the available evidence, courses of CBT and (to a lesser extent) one or two sessions of MI improved outcomes in a self-selected population of cannabis users. There was some evidence that contingency management enhanced long-term outcomes in combination with CBT. Results of CBT for cannabis cessation in psychiatric populations were less promising, but may have been affected by provision of TAU in both groups and the referred populations. Future research should focus on the number of CBT/MI sessions required and potential clinical effectiveness and cost-effectiveness of shorter interventions. CBT plus contingency management and mutual aid therapies warrant further study. Studies should consider potential effects of recruitment methods and include inactive control groups and long-term follow-up. TAU arms in psychiatric population studies should aim not to confound the study intervention.Study RegistrationThis study is registered as PROSPERO CRD42014008952.FundingThe National Institute for Health Research HTA programme.

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