Cannabidiol had beneficial effects as an adjunctive therapy in patients with schizophrenia, research findings suggest.
“The first evidence that [cannabidiol] might be useful in treating schizophrenia came from a case report in which it was found to improve symptoms in a patient who had not responded to haloperidol,” Philip McGuire, FRCPsych, FMedSci, professor of psychiatry and cognitive neuroscience in the department of psychosis studies, and the Institute of Psychiatry, Psychology and Neuroscience at King’s College London, and colleagues wrote in The American Journal of Psychiatry. “The mechanism of action on [cannabidiol] is unclear, but it does not appear to involve the direst antagonism of dopamine receptors.”
Researchers conducted a double-blind parallel-group trial to determine the safety and effectiveness of cannabidiol in patients with schizophrenia after 6 weeks of treatment. In a 1:1 ratio, they randomly assigned 43 participants to receive 1,000 mg daily cannabidiol and 45 to receive placebo alongside their existing antipsychotic medication, with improvement measurements taken before and after treatment.
Analysis showed that cannabidiol was well-tolerated. Compared with patients who received placebo, those who took cannabidiol had lower levels of positive psychotic symptoms (PANSS: treatment difference = –1.4; 95% CI, –2.5 to –0.2), and were more likely to have been clinically considered improved (CGI-I: treatment difference = –0.5; 95% CI, –0.8 to –0.1) and not severely unwell (CGI-S: treatment difference = –0.3; 95% CI, –0.5 to 0). In addition, patients in the cannabidiol group demonstrated greater improvements in cognitive performance (BACS: treatment difference = 1.31; 95% CI, –0.1 to 2.72) and in overall functioning (GAF: treatment difference = 3; 95% CI, –0.4 to 6.4), although these were not statistically significant. Furthermore, cannabidiol’s effects did not appear to depend on dopamine receptor antagonism. The cannabidiol and placebo groups saw similar rates of adverse events, with only one-third of patients in each group reporting treatment-emergent adverse effects.
“Although the magnitude of the effect on positive symptoms was modest, it was seen in patients who were already being treated with antipsychotic medication at appropriate dosages; the improvement was thus over and above the effect of antipsychotic treatment,” McGuire and colleagues wrote. “Because [cannabidiol] acts in a way different from conventional antipsychotic medication, it may represent a new class of treatment for schizophrenia. However, its potential clinical utility will require further investigation in larger-scale trials.” – by Savannah Demko
McGuire reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.