Testing the Efficacy of the Cannabis Clinic for Patients With Psychosis (CCP) Intervention for Cannabis Use Reduction/Cessation in Patients With First Episode Psychosis (FEP)

Schizophrenia and other psychotic disorders are major causes of chronic ill health and early death. Daily use of high-potency cannabis significantly increases the risk of developing these disorders - up to ninefold - and also worsens outcomes and cognitive function. In the UK, it is estimated that 30-50% of patients presenting with their first episode of psychosis have been using cannabis. Approximately half of these patients continue using cannabis, and those who do are more likely to relapse, experience compulsory and longer admission hospital admissions, and experience more pronounced cognitive effects compared to those who abstain. Regardless of the clear need, there are currently few targeted interventions designed to support individuals with psychosis dependent on cannabis.

To address this urgent gap, in 2019, the first Cannabis Clinic for Psychosis (CCP) was created in the South London and Maudsley NHS Foundation Trust (SLaM) (CCP; maudsleycharity.org/case-studies/cannabis-clinic/). Cannabis use is the most modifiable risk factor for poor clinical outcomes in psychosis with strong evidence linking it to earlier illness onset, more severe symptoms and increased rates of relapse and hospitalisation. Often this population fall into two services: general adult psychiatric services or services for addiction with neither offering an intervention that addresses cannabis use directly. Despite the evidence of cannabis use having a severe impact on the outcome of people navigating psychotic disorders, there is still a lack of treatment available.

Although problematic cannabis use is becoming a significant clinical concern especially among patients with psychosis, there are currently no established treatment guidelines for this clinical population. Currently, the NICE guideline for psychosis recommends a combination of antipsychotics and general management of substance misuse, without specifically addressing the frequent co-morbidity with cannabis use disorder. This underscores a critical gap in care for individuals with psychotic disorders who are actively using cannabis while experiencing their first onset psychosis. In her Independent Review of Drugs, Professor Dame Carol Black recommended that individuals with cooccurring mental health and substance use disorders should receive integrated, concurrent treatment for both conditions. The CCP intervention offers this.

The proposed study is a waiting list randomised controlled trial (RCT) that aims to evaluate the clinical efficacy of the CCP intervention. Participants (n=80) will be adults (aged 18 and over) currently under the care of SLaM Early Intervention Teams for first onset psychosis, who are dependent on cannabis (CUDIT-R score =>9) and express an intention to reduce or stop their use. They will be randomised to either the intervention group (n=40) or the waiting list control group receiving Treatment As Usual (TAU) (N=40). The intervention comprises 12 weekly (+/- 4 weeks) one-to-one sessions, each lasting up to 60 minutes with optional participation in a weekly online peer group based on the CCP recently published proof of concept paper (POC). Sessions are delivered by trained clinicians and include evidence-based psychosocial techniques, including Motivational Interviewing (MI), Cognitive Behavioural Therapy (CBT), and personalised support for co-occurring tobacco use. The treatment is non-pharmacological and administered via participant-led approach that accommodates online or face-to-face sessions to meet the patient preference. Qualitative data from the recent CCP POC paper indicate that the flexibility in allowing patients choice on the session's modality (online/face to face, hybrid) increased and maintained engagement.

The CCP RCT primary outcome will measure, in all participants, changes in the Cannabis Use Disorders Identification Test-Revised (CUDIT-R) score between baseline (before randomisation) and at post-intervention T1 16 weeks after baseline. Other cannabis measures data will be collected at the same time points to assess pattern of use. Secondary outcomes include changes in psychosis symptoms dimensions, paranoia, depression, anxiety, cognitive and overall functioning. Previous findings from the POC analyses of the CCP intervention showed that the CUDIT-R scores, measure of Cannabis Dependence dropped from a baseline mean score 17.88 (5.15), well above the threshold for dependence (=>9) to a post intervention mean score 1.20 (2.10). 74% of participants achieved abstinence, with significant improvements across all secondary outcomes and over 90% returning to work or education. Therefore, the proposed RCT aims to formally test both the efficacy and the safety of the CCP intervention compared to a control group. Data from the CCP POC paper support an expected low risk posed to participants since the intervention is psychosocial in nature and aligned with standard care practices.