STEP-ASSIST

• Research type

  Research Study

• Full title

  CANNABIDIOL AUGMENTATION OF CLOZAPINE IN TREATMENT RESISTANT PSYCHOSIS: A DOUBLE BLIND RANDOMISED CONTROLLED TRIAL

• IRAS ID

  1007007

• Contact name

  Philip McGuire

• Contact email

  philip.mcguire@psych.ox.ac.uk

• Sponsor organisation

  Research Governance, Ethics and Assurance, University of Oxford

• Research summary

  The purpose of this trial is:
  • To investigate whether the response to clozapine treatment can be enhanced by adding cannabidiol (CBD), compared to placebo, in treatment resistant psychosis patients.
  • To confirm the safety of CBD in people with psychosis.

  The trial is a randomised, double-blind, placebo-controlled, multi-centre, clinical trial. Individuals with a diagnosis of treatment resistant psychosis in their illness who have had a suboptimal or no response to clozapine treatment will be recruited. These patients are randomised to treatment with oral CBD 500mg twice daily, or a matching placebo for 12 weeks, next to clozapine, the participant’s standard care treatment. By using a battery of clinical outcome assessments, the trial will assess several optional biomarkers to predict clinical outcomes and response to treatment with CBD. Participants will be invited to provide additional blood samples, stool samples, and complete neuroimaging assessments.

• REC name

  South Central - Hampshire B Research Ethics Committee

• REC reference

  25/SC/0297

• Date of REC Opinion

  30 Oct 2025

• REC opinion

  Further Information Favourable Opinion