Rationale

Preliminary evidence suggests that cannabidiol (CBD) may be effective in the treatment of neurodegenerative disorders; however, CBD has never been evaluated for the treatment of cognitive impairments associated with schizophrenia (CIAS).

Objective

This study compared the cognitive, symptomatic, and side effects of CBD versus placebo in a clinical trial.

Methods

This study was a 6-week, randomized, placebo-controlled, parallel group, fixed-dose study of oral CBD (600 mg/day) or placebo augmentation in 36 stable antipsychotic-treated patients diagnosed with chronic schizophrenia. All subjects completed the MATRICS Consensus Cognitive Battery (MCCB) at baseline and at end of 6 weeks of treatment. Psychotic symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS) at baseline and biweekly.

Results

There was no main effect of time or drug on MCCB Composite score, but a significant drug × time effect was observed (p = 0.02). Post hoc analyses revealed that only placebo-treated subjects improved over time (p = 0.03). There was a significant decrease in PANSS Total scores over time (p < 0. 0001) but there was no significant drug × time interaction (p = 0.18). Side effects were similar between CBD and placebo, with the one exception being sedation, which was more prevalent in the CBD group.

Conclusions

At the dose studied, CBD augmentation was not associated with an improvement in MCCB or PANSS scores in stable antipsychotic-treated outpatients with schizophrenia. Overall, CBD was well tolerated with no worsening of mood, suicidality, or movement side effects.

Trial registration

https://clinicaltrials.gov/ct2/show/NCT00588731