Evidence-Based Reviews

Cannabidiol for psychosis: A review of 4 studies

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1. McGuire P, Robson P, Cubala WJ, et al. Cannabidiol (CBD) as an adjunctive therapy in schizophrenia: a multicenter randomized controlled trial. Am J Psychiatry. 2018;175(3):225-231.

Antipsychotic medications act through blockade of central dopamine D2 receptors. For most patients, antipsychotics effectively treat positive psychotic symptoms, which are driven by elevated dopamine function. However, these medications have minimal effects on negative symptoms and cognitive impairment, features of schizophrenia that are not driven by elevated dopamine. Compounds exhibiting a mechanism of action unlike that of current antipsychotics may improve the treatment and outcomes of patients with schizophrenia. The mechanism of action of CBD is unclear, but it does not appear to involve the direct antagonism of dopamine receptors. Human and animal research study findings indicate that CBD has antipsychotic properties. McGuire et al4 assessed the safety and effectiveness of CBD as an adjunctive treatment of schizophrenia.

Study design

  • In this double-blind parallel-group trial conducted at 15 hospitals in the United Kingdom, Romania, and Poland, 88 patients with schizophrenia received CBD (1,000 mg/d; N = 43) or placebo (N = 45) as adjunct to the antipsychotic medication they had been prescribed. Patients had previously demonstrated at least a partial response to antipsychotic treatment, and were taking stable doses of an antipsychotic for ≥4 weeks.
  • Evaluations of symptoms, general functioning, cognitive performance, and EPS were completed at baseline and on Days 8, 22, and 43 (± 3 days). Current substance use was assessed using a semi-structured interview, and reassessed at the end of treatment.
  • The key endpoints were the patients’ level of functioning, severity of symptoms, and cognitive performance. Participants were assessed before and after treatment using the PANSS, the Brief Assessment of Cognition in Schizophrenia (BACS), the Global Assessment of Functioning scale (GAF), and the improvement and severity scales of the Clinical Global Impressions Scale (CGI-I and CGI-S, respectively).
  • The clinicians’ impression of illness severity and symptom improvement and patient- or caregiver-reported impressions of general functioning and sleep also were noted.


  • After 6 weeks, compared with the placebo group, the CBD group had lower levels of positive psychotic symptoms and were more likely to be rated as improved and as not severely unwell by the treating clinician. Patients in the CBD group also showed greater improvements in cognitive performance and in overall functioning, although these were not statistically significant.
  • Similar levels of negative psychotic symptoms, overall psychopathology, and general psychopathology were observed in the CBD and placebo groups. The CBD group had a higher proportion of treatment responders (≥20% improvement in PANSS total score) than did the placebo group; however, the total number of responders per group was small (12 and 6 patients, respectively). At baseline, most patients in both groups were classified as moderately, markedly, or severely ill (83.4% in the CBD group vs 79.6% in placebo group). By the end of treatment, this decreased to 54.8% in the CBD group and 63.6% in the placebo group. Clinicians rated 78.6% of patients in the CBD group as “improved” on the CGI-I, compared with 54.6% of patients in the placebo group.


  • CBD treatment adjunctive to antipsychotics was associated with significant effects on positive psychotic symptoms and on CGI-I and illness severity. Improvements in cognitive performance and level of overall functioning were also seen, but were not statistically significant.
  • Although the effect on positive symptoms was modest, improvement occurred in patients being treated with appropriate dosages of antipsychotics, which suggests CBD provided benefits over and above the effect of antipsychotic treatment. Moreover, the changes in CGI-I and CGI-S scores indicated that the improvement was evident to the treating psychiatrists, and may therefore be clinically meaningful.

Continue to: Boggs DL, et al...


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