Cannabidiol as an adjunctive therapy in schizophrenia
Authors: McGuire P et al.
Summary: This multi-centre, double-blind, randomised controlled trial followed on from promising animal
studies to investigate the antipsychotic efficacy of cannabidiol (CBD) in schizophrenic patients. 88 patients
were randomised 1:1 to receive either 1000mg/day CBD (n=43) or placebo (n=45) for 6 weeks in addition to
their regular antipsychotic medication. Psychotic symptoms were quantified pre and post-treatment using the
Positive and Negative Syndrome Scale (PANSS), the Brief Assessment of Cognition in Schizophrenia, the Global
Assessment of Functioning scale and the improvement and severity scales of the Clinical Global Impressions
Scale (CGI-I and CGI-S). CBD showed beneficial effects in patients with schizophrenia including decreased
levels of positive psychotic symptoms (PANSS: treatment difference=−1.4, 95% CI=−2.5, −0.2) and increased
physician-rated “not as unwell” scores (CGI-S: treatment difference=−0.3, 95% CI=−0.5, 0.0). CBD was well
tolerated with no notable adverse effects.
Comment: It may seem counter-intuitive to many clinicians that a constituent from cannabis may actually
be a useful adjunctive treatment in schizophrenia, as consistent data has shown that there is an increased
risk in some people of developing a psychotic disorder from cannabis use. It is important to note that this is
primarily associated with Tetrahydrocannabinol (THC), THC analogues, and THC-rich strains of cannabis.
There appears, however, to be a role for other cannabinoids such as CBD, which does not have a direct
affinity with the psychotropic CB1 receptor. It is of note that this study revealed that CBD in fact reduced
‘positive’ symptoms of schizophrenia, which incidentally typify some of the symptoms that occur in high THC
use (e.g. visual and auditory hallucinations, paranoia etc.). Further work is needed to assess this therapeutic
approach in a longer-term study to assess whether a treatment effect is maintained. It is also of potential
interest to see if other medicinal cannabis constituents may enhance this effect, and whether a low-THC
full spectrum whole plant effect can achieve similar or more beneficial outcomes.
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