Abstract
Background/Objectives: Major depressive disorder (MDD) is often characterized by mood instability and occupational imbalance, leading to impaired functioning and reduced quality of life. Despite increasing recognition of occupational therapy's (OT's) role in mental health, few interventions comprehensively describe both their development process and their theoretical rationale. This article aims to present the systematic development of the mood-occupation balance reciprocal model (MOBILE) intervention for people with MDD, guided by the Medical Research Council (MRC) framework for complex intervention. Methods: Development followed three phases: (1) identifying the evidence base, (2) developing theory, and (3) modeling processes and outcomes. Theoretical foundations integrated occupation- and mood/function-based models with client-centered, lived-experience perspectives. A preliminary ecological momentary assessment (EMA) study on mood and daily function interplay further informed the intervention development. Input from focus groups with occupational therapists and individuals with lived experiences supported its iterative refinement. Following MRC guidelines, a small pilot study (N = 2) was conducted with inpatients diagnosed with MDD to assess the feasibility and acceptability of the intervention and EMA procedures. The pilot evaluated recruitment, adherence, engagement, and practicality of delivery within a clinical setting. Results: The pilot study, although it included only two inpatients and thus limits generalizability, demonstrated high adherence, engagement, and feasibility. The EMA protocol was well tolerated, leading to minor refinements that enhanced its clinical applicability. Stakeholders emphasized the program's relevance, adaptability, and the value of personalized planning tools. Conclusions: The MOBILE intervention is delivered as an individualized program to enhance mood stability and daily functioning among inpatients with MDD. It provides a theoretically grounded, context-sensitive framework integrating personalized goal setting and strategy use with the construction of a balanced routine. Implications: This article provides a comprehensive account of development procedures to support future evaluation, implementation, and integration into OT mental health practice.