Investigating the mobile messenger app-based intervention delivered by a therapeutic companion agent for young adults with depressive symptoms: A proof-of-concept and quasi-experimental study.

BACKGROUND: Despite the clinical potential of digital interventions for young adults with depression, low engagement remains a persistent challenge. A conversational therapeutic companion agent (TCA) can foster a digital therapeutic alliance to address this barrier. OBJECTIVE: This study aimed to develop a Wizard-of-Oz TCA prototype integrating behavioral activation, ecological momentary assessment/intervention (EMA/EMI), and gamification, and to evaluate its proof-of-concept feasibility, acceptability, and preliminary clinical efficacy for young adults with depressive symptoms. METHODS: 58 Korean young adults ages 20 to 39 (50.0% female) with subclinical to moderately severe depressive symptoms (Patient Health Questionnaire-9) were recruited. The intervention group (n=29) interacted with the TCA for six weeks, while a frequency-matched passive control group (n=29) continued usual routines. Primary outcomes were feasibility (adherence) and acceptability (satisfaction). Secondary outcomes for efficacy (Beck Depression Inventory-II, Generalized Anxiety Disorder-7, Quality-of-Life Enjoyment and Satisfaction Questionnaire-Short Form) were assessed biweekly. RESULTS: Of 58 participants, 57 completed the study. The intervention proved feasible, acceptable, and usable, achieving 69.5% strict on-time EMA adherence, 66.2% behavioral activation routine completion, a mean daily satisfaction of 3.49/5.0, and a mean System Usability Scale (SUS) score of 74.02, meeting a priori benchmarks. Exploratory analyses indicated the intervention group showed significantly greater reductions in depressive symptoms and improvements in quality of life compared to controls. CONCLUSIONS: The TCA-based intervention is feasible and acceptable, successfully cultivating a digital therapeutic alliance. While preliminary clinical signals are promising, future fully powered randomized controlled trials are required to definitively establish clinical efficacy.