Clinical practice guidelines and quality standards for early intervention in psychosis: an AGREE II appraisal and systematic review of service components

Background: Early intervention in psychosis (EIP) is a key component of youth mental health care, yet recommended models of care for individuals at clinical high risk for psychosis (CHR-P) and first-episode psychosis (FEP) remain heterogeneous across jurisdictions. No previous study has combined a formal AGREE II appraisal with a structured synthesis of core service components for EIP. Methods: We conducted a systematic review and AGREE II-based appraisal of international clinical practice guidelines (CPGs) and quality standards (QSs). MEDLINE (via PubMed), the Cochrane Library (CENTRAL), Web of Science, guideline repositories, and grey literature sources were searched to March 2025 in accordance with PRISMA 2020 guidance. Eligible documents were CPGs or QSs published in English or Italian from 2005 onward containing recommendations on the organization, assessment, and treatment of CHR-P and/or FEP. Methodological quality was appraised with AGREE II (inter-rater agreement assessed using ICCs); recommendations were extracted, and core components required endorsement by at least one third of relevant documents with at least one strong or mandatory recommendation. Twenty-six documents (24 CPGs and 2 QSs) were included. Methodological quality was moderate overall, with substantial variability across AGREE II domains: scores were generally strongest for scope and purpose, stakeholder involvement, and clarity of presentation, and more variable for Rigour of development, applicability, and editorial independence. Results: We identified 32 core recommendations. For CHR-P, the most consistent components were specialized services or dedicated pathways, comprehensive multidisciplinary assessment, cognitive-behavioural therapy, family interventions, and a cautious approach to antipsychotic use. For FEP, the most consistently endorsed components were specialized multidisciplinary teams, assertive and continuous follow-up, family work, psychoeducation, structured pharmacological monitoring, and supported education and employment. Conclusion: These findings provide a guideline-derived framework for youth EIP service delivery and model development, while highlighting the need for more methodologically robust and implementation-oriented guidance across settings. Systematic review registration: https://osf.io/cek7u, identifier cek7u.