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: 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.