Effect of experimental endocannabinoid modulation on brain function in individuals at high risk for psychosis

INTERVENTION: Participants will be randomly allocated to one of the two treatment arms using a blocked randomisation list with a 1:1 allocation ratio. Intervention arm: Participants receive oral administration of a single capsule containing 600mg of cannabidiol, to be taken once in a day in the morning for a total of 21 days. Control arm: Participants receive oral administration of a single matched placebo capsule, to be taken once a day in the morning for 21 days. Final follow‐up assessment for all the treatment arms to be carried out on day 21 of the study which is also the final intake of the study drug. CONDITION: Ultra high risk for psychosis ; Mental and Behavioural Disorders ; Ultra high risk for psychosis PRIMARY OUTCOME: fMRI BOLD signal in the hippocampus, striatum and amygdala measured during the memory, salience and emotional (fear) processing tasks on day 1 and day 21. SECONDARY OUTCOME: Plasma endocannabinoid (Anandamide, 2‐AG, OEA, PEA) levels measured on day 1 (110 minutes following drug administration on day 1) and day 21 (110 minutes following administration of the last dose of the drug).; INCLUSION CRITERIA: 1. Aged 18‐ 35 years 2. Right‐handed 3. Ultra high risk (UHR) for psychosis individuals being supported by OASIS (www.oasislondon.com), a large clinical service for this group 4. Have positive psychotic symptoms and anxiety symptoms, as defined using the Positive and Negative syndrome scale(PANSS) and the State‐Trait Anxiety Inventory (STAI) 5. Medication naïve