The purpose of this trial is:
* To investigate whether cannabidiol (CBD), compared to placebo, can reduce the severity of attenuated psychotic symptoms in individuals at clinical high risk for psychosis. * To confirm the safety of CBD in individuals at clinical high risk for psychosis.
The trial is a randomised, double-blind, placebo-controlled, multi-centre, international clinical trial. Individuals meeting clinical high risk for psychosis criteria will be recruited for the trial intervention component of the trial. Participants are randomised to treatment with oral CBD 300mg (oral solution 100 mg/mL) twice daily, or a matching placebo, for 104 weeks. By using a battery of clinical outcome assessments, the trial will be able to assess several biomarkers to predict clinical outcomes and response to treatment with CBD. Participants will be invited to provide blood samples, stool samples, cerebrospinal fluid samples (if aged 18 years or over) and complete neuroimaging assessments. Individuals who are not found to have mental illness as defined by DSM-5 criteria will be recruited to a healthy control group, to validate the biomarker component of the trial.
Additionally, a control group of healthy volunteers will be recruited who will not take the trial intervention to aid calibration between datasets from sites acquiring MRI data and to inform and validate any possible multivariate signature associated with the CHR-P state, course or outcome by understanding how these measures are different in controls. Healthy controls will also be used for secondary case-control comparisons. Healthy controls will undergo clinical and biomarker assessments only.
12 to 35 years of age inclusive, willing and able to provide written informed consent/assent.
Meet criteria for either the Attenuated Psychotic Symptoms (APS) or Brief Limited Intermittent Psychotic Symptoms (BLIPS) subgroups of the CHR-P state, defined using the CAARMS (PSYSCAN version), which also integrates the SIPS criteria. Inter-rater reliability will be ensured throughout via an ongoing training programme for the researchers at each site.
The participant is currently not participating and is not expecting to start participation during the current trial in another intervention trial (e.g. medication, medical device, psychological intervention).
Participants of childbearing potential* must be willing to ensure that they use highly effective contraception during the trial as per the requirements in the protocol**
Previous neurosurgery or neurological disorder, including epilepsy, which may affect the trial procedures;*
Pregnancy or breastfeeding;
The participant is unable to fully comprehend the purpose of the trial or make a rational decision whether or not to participate;
IQ<70 as measured by a validated IQ test e.g. WASI, WAIS, WISC, as approved for local languages and appropriate for the participant's age;