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The prevalence and negative influence of depressive symptoms on individuals with substance use disorders, combined with the knowledge that certain behavior change processes are related to abstinence, create the need for research to understand how depressive symptoms, the addictive behavior change process, and drug use outcomes are related. The purpose of this study was to test a model predicting drug use outcome during a treatment episode in which depressive symptoms were mediated by three behavior change process measures: 1) motivation to change; 2) behavioral coping processes of change; and 3) abstinence self-efficacy. It was hypothesized that greater depressive symptoms would increase drug use both directly and indirectly through the hypothesized decrease in behavior change processes. Seventy-two participants attending outpatient drug use disorder treatment and participating in a larger study named the STOP Project were included in these secondary analyses. Traditional mediation testing with OLS regression and bootstrapped mediation analyses were used to test the model. Results supported the fit of the hypothesized model. The statistical significance testing supported the following relations: greater depressive symptoms increased drug use outcome; greater depressive symptoms decreased behavior change processes; and decreased behavior change processes increased drug use. Treatment site, a covariate in the model, significantly predicted both increased use of behavioral coping processes and decreased drug use post-treatment. These findings support existing literature which highlights the role of depressive symptoms affecting drug use outcomes. The findings further support the existing literature indicating an important role for behavior change processes on drug use outcome. The current findings add to the literature by examining a more complex mediation model of influence that highlights how depressive symptoms impair important behavior change processes. Depressive symptoms demonstrated both direct and indirect effects of increased drug use outcome. Depressive symptoms negatively influenced critical change producing mechanisms by reducing motivation to change, coping behaviors, and confidence, leading to increased drug use. Behavioral coping processes alone mediated the relation between depressive symptoms and drug use. Results are discussed in terms of both clinical and research significance.