Background <p>Individuals with substance use disorders (SUD) can experience different factors influencing addiction. Personalized networks and descriptive graphs based on ecological momentary assessment (EMA) could uncover individual mechanisms, facilitating personalized psychotherapy. We tested a feedback application (fb-app) using EMA to improve client-practitioner communication in SUD interventions.</p> Methods <p>One participant experiencing cannabis use problems completed EMA regarding substance use and related factors five times daily over 22 days. A clinical psychologist and a researcher generated personalized descriptive graphs and networks using the fb-app. The psychologist discussed these results with the participant using motivational interviewing (MI) techniques. Semi-structured interviews with the participant and psychologist, analyzed with thematic analysis, assessed usefulness, ease of use, and related concepts.</p> Results <p>EMA-based feedback seemed a feasible and promising add-on to MI. The participant reported improved understanding of his cannabis use. The psychologist noticed improved therapeutic communication, but also that the fb-app needed simplification for independent clinical use. An fb-app error duplicated data, risking false associations in the networks, suggesting alternative explanations of reported network usefulness other than providing accurate information.</p> Conclusions <p>EMA-based feedback in MI for addiction seems promising and feasible enough to justify larger studies investigating its impact on behavior change and which types of feedback work best and why.</p>