Expert guide to preventing psychosis in young cannabis users at risk

To prepare evidence-based guidelines on psychosis prevention. We reviewed evidence on risk factors for/age at onset of psychosis, tools to assess clinical high-risk of psychosis (CHR-P), transition rates, risk calculation/ethical considerations around risk communication, CHR-P biological/clinical correlates, efficacy/cost-effectiveness of interventions/psychosis prevention services. The World Federation of Societies of Biological Psychiatry framework was used to grade evidence regarding interventions/services, elaborating guidelines with evidence-/consensus-based clinical recommendations to prevent psychosis in CHR-P subjects. At the service organisation level, (i) psychosis indicated prevention services might be implemented in close collaboration with early intervention services for psychosis to minimise duration of untreated illness, (ii) intake age criteria should be between 14 to 35, (iii) services should allow access to persons with cannabis use disorder. At the assessment and risk communication level, in clinical settings: (iv) staff in mental health services should be trained in administering/rating CHR-P assessment tools, (v) administer them, (vi) be trained in using/interpreting risk calculators, and (vii) in communicating risk, (viii) only use validated risk calculators, keeping a human-to-human interaction. Also, (ix) prevention services should assess comorbid mental disorders. At the intervention level: (x) staff should offer treatment for abstinence from cannabis, (xi) offer evidence-based treatment for comorbid mental disorders, and (xii) offer treatment for CHR-P based on patient preference, following the 'first do no harm' principle. Prevention services should be implemented, including interventions for cannabis use, reducing the duration of untreated psychosis, and treating comorbid mental disorders.