The effects of cannabidiol (CBD) on cognition and symptoms in outpatients with chronic schizophrenia a randomized placebo controlled trial

Psychopharmacology (Berl). 2018 Jul;235(7):1923-1932. doi: 10.1007/s00213-018-4885-9. Epub 2018 Apr 5.


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:

Keywords: Attention; CBD; Cannabidiol; Cannabinoids; Cognition; Memory; Psychosis; Schizophrenia.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Adult
  • Affect / drug effects
  • Affect / physiology
  • Antipsychotic Agents / administration & dosage
  • Cannabidiol / administration & dosage*
  • Chronic Disease
  • Cognition / drug effects
  • Cognition / physiology
  • Cognitive Dysfunction / diagnosis
  • Cognitive Dysfunction / drug therapy*
  • Cognitive Dysfunction / psychology*
  • Double-Blind Method
  • Female
  • Follow-Up Studies
  • Humans
  • Male
  • Mental Status and Dementia Tests
  • Middle Aged
  • Outpatients / psychology*
  • Psychiatric Status Rating Scales
  • Schizophrenia / diagnosis
  • Schizophrenia / drug therapy*
  • Schizophrenic Psychology*
  • Treatment Outcome


  • Antipsychotic Agents
  • Cannabidiol

Associated data