Legitimacy, Embedding, and Learning: A Framework for Scaling Up Complex Psychosocial Interventions

Objective: To propose a multi-level framework to facilitate the sustainment and scale-up of complex evidence-based psychosocial interventions across mental health, social care, and employment systems. Methods: Integrative review of 41 empirical studies on contextual determinants of Individual Placement and Support (IPS) sustainment and scale-up, interpreted through implementation science, policy implementation research, and welfare policy literature. Results: Three mechanisms were identified as crucial for sustaining and scaling up: Policy Legitimacy: normative acceptability and institutional compatibility that enables mandates and political-administrative authorization; Policy Embedding: coherence of multi-level, cross-sector governance arrangements that routinise the intervention beyond pilots; and Policy Learning: cumulative implementation evidence infrastructure enabling comparable measurement, feedback, and authorized adaptation. Conclusion: The proposed Legitimacy–Embedding–Learning (LEL) Framework for Scale-Up holds that scaling complex interventions is a configuration challenge within complex systems, rather than a linear dissemination task. The framework may support proactive adaptation when scaling IPS and similar interventions.