Stratification and Treatment in Early Psychosis Study -ASSIST

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, international, 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, in addition to clozapine, which is standard care treatment for this population. 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. Biomarkers are being assessed as an exploratory outcome measure. Participants will be invited to provide additional blood samples, stool samples, and complete neuroimaging assessments.

NCT Number	NCT07326124
Lead Sponsor	University of Oxford Collaborators: Wellcome Trust, Cambridge Cognition Ltd, Cambridgeshire and Peterborough NHS Foundation Trust, Oxford Health NHS Foundation Trust, West London NHS Trust, Charite University, Berlin, Germany, University of Cologne, Ludwig-Maximilians - University of Munich, University Hospital Frankfurt, Department of Psychiatry, Psychosomatic Medicine and Psychotherapy, The Sheba Fund for Health Services and Research, Shalvata Mental Health Center, Geha Mental Health Center, Amsterdam University Medical Center, National and Kapodistrian University of Athens, Hospital General Universitario Gregorio Marañon, Hospitales Universitarios Virgen del Rocío, University of Campania Luigi Vanvitelli, Psychiatric University Hospital, Zurich, Douglas Hospital Research Centre
Conditions	Treatment Resistant Psychosis, Psychosis
Enrollment	250 participants
Start Date	2026-06
Primary Completion	2028-09 (estimated)
Study Completion	2029-09 (estimated)
Updated on ClinicalTrials.gov	2026-01-08