Bridging Psychiatry and Addiction Medicine: Integrated Care Models for the Management of Severe Mental Illness and Substance Use Disorders

Abstract Background: Co-occurring severe mental illness and substance use disorders pose enduring challenges for health systems due to diagnostic complexity, fragmented service delivery, and inconsistent treatment pathways. Although integrated care has gained attention as a strategy to address these challenges, diversity in model design and variability in implementation have limited consensus on best practices and scalability across healthcare settings. Methods: A scoping review was conducted in accordance with established methodological frameworks and PRISMA-ScR guidance. Systematic searches of major electronic databases identified studies examining integrated psychiatric and addiction care across inpatient, outpatient, community-based, and primary care–linked settings. Eligible studies included quantitative, qualitative, and mixed-methods designs. Data were charted and synthesized narratively to map care model typologies, core components, implementation contexts, and outcomes. Results: The evidence base demonstrated heterogeneity in study design, geographic distribution, and healthcare context. Integrated care models varied in structure and intensity, including multidisciplinary team-based approaches, collaborative care frameworks, and community-oriented interventions. Despite this variability, shared features included coordinated treatment planning, cross-disciplinary collaboration, and continuity of care. Integrated approaches were associated with favorable trends in psychiatric stability, substance-related outcomes, and health service utilization. Key limitations included short follow-up periods and heterogeneity in outcomes. Conclusion: Integrated care provides a coherent framework for addressing the complex needs of individuals with co-occurring severe mental illness and substance use disorders. However, variability in implementation and persistent evidence gaps underscore the need for standardized outcome measures, context-sensitive adaptation, and stronger integration.