Cannabis and schizophrenia

Rathbone J, Variend H, Mehta H

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Summary

Cannabis for schizophrenia

Schizophrenia usually begins in young adulthood and has a lifetime prevalence of about 1% irrespective of culture, social class and race. Schizophrenia is typically a chronic relapsing mental illness, characterized by hallucinations, delusions, disordered thinking, and emotional withdrawal. The effect of cannabis in exacerbating or improving the symptoms of schizophrenia is controversial; some studies report that people using cannabis have a higher risk of experiencing a psychotic episode.

We aimed to review the effects of cannabis use on people with schizophrenia and schizophrenia-like illnesses. We sought randomised trials comparing cannabis/cannabinoid compounds with standard care, or no treatment in people with schizophrenia. We included one study. Outcome data were limited and did not reveal any significant differences between groups.

This is a Cochrane review abstract and plain language summary, prepared and maintained by The Cochrane Collaboration, currently published in The Cochrane Database of Systematic Reviews 2008 Issue 3, Copyright © 2008 The Cochrane Collaboration. Published by John Wiley and Sons, Ltd.. The full text of the review is available in The Cochrane Library (ISSN 1464-780X).
This record should be cited as: Rathbone J, Variend H, Mehta H. Cannabis and schizophrenia. Cochrane Database of Systematic Reviews 2008, Issue 3. Art. No.: CD004837. DOI: 10.1002/14651858.CD004837.pub2

This version first published online: July 16. 2008

Abstract

Background

Many people with schizophrenia use cannabis and its effects on the illness are unclear.

Objectives

To evaluate the effects of cannabis use on people with schizophrenia and schizophrenia-like illnesses.

Search strategy

We searched the Cochrane Schizophrenia Group Trials Register (April 2007) which is based on regular searches of BIOSIS, CENTRAL, CINAHL, EMBASE, MEDLINE and PsycINFO.

Selection criteria

We included all randomised trials involving cannabinoids and people with schizophrenia or schizophrenia-like illnesses.

Data collection and analysis

We extracted data independently. For dichotomous data we calculated relative risks (RR) and their 95% confidence intervals (CI) on an intention-to-treat basis, based on a fixed effects model. We calculated the numbers needed to treat/harm (NNT/NNH). For continuous data, we calculated weighted mean differences (WMD) again based on a fixed effects model.

Main results

We identified one randomised trial. No significant differences were found between the Cannabis and Psychosis Therapy (CAP) intervention group and the Psychoeducaton (PE) intervention for use of cannabis at three months assessment (n=47, RR 1.04 CI 0.6 to 1.7). BPRS-extended scale scores at three months assessment (n=47, WMD -3.60 CI -12.8 to 5.6) and nine months assessment (n=47, WMD 0.80 CI -7.5 to 9.1) were non-significant between CAP and PE. We found no significant improvement in social functioning in the CAP group compared with PE (at 3 months, n=47, WMD -0.80 CI -10 to 8.4) and (at 9 months, n=47, WMD -4.70 CI -14.5 to 5.1).

Authors' conclusions

At present, there is insufficient evidence to support or refute the use of cannabis/cannabinoid compounds for people suffering with schizophrenia. This review highlights the need for well designed, conducted and reported clinical trials to address the potential effects of cannabis based compounds for people with schizophrenia.

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