Date of Award

Spring 5-2-2019

Document Type


Degree Name

Doctor of Philosophy in Clinical Psychology (PhD)


Clinical Psychology

First Advisor/Committee Member

David G. Stewart, PhD

Second Advisor/Committee Member

Amy Mezulis, PhD

Third Advisor/Committee Member

Elizabeth LoTempio, PsyD

Fourth Advisor/Committee Member

Keyne Law, PhD


The comorbidity of substance use and depression among adolescents has been strongly established but less is known about their reciprocal impact over time. Examining these variables in the context of an intervention provides information about how changes in one effect the other. The current study examines the effect of a school-based Motivational Interviewing (MI) intervention, Project READY, on co-occurring substance use and depressive symptoms in adolescents (N = 103; ages 13-18, mean = 16) from the greater Seattle area. We hypothesized: (a) the quantity and frequency of substance use will decrease from pre-treatment to post-treatment follow up; (b) the number of substance-related consequences will decrease from pre-treatment to post-treatment follow up; (c) depression symptoms will decrease from pre-treatment to post-treatment follow up; and (d) a reduction in substance use from pre-treatment to post-treatment, and the subsequent reduction in substance use consequences, will predict a reduction in depression symptoms at post-treatment follow up compared to pre-treatment levels. Participants were diverse in ethnicity with Caucasian (32%), Asian American (22%), Hispanic (18%), African American (11%), Multiethnic (10%), and Native American/Alaskan Native (1%) adolescents represented in the sample. The sample mostly included male participants (70%). Three serial mediation analyses were conducted, examining change in substance use and change in consequences of substance use as mediating the effect of the intervention on change in depression symptoms. Total substance use (alcohol and marijuana), alcohol use, and marijuana use were examined as three separate models. We found that the analysis examining marijuana use only was statistically significant. The indirect effect of the intervention on depression symptoms through marijuana consequences (B = -1.416, CI95 = -3.083 to -0.132) was significantly stronger (B = -1.154, CI95 = -2.657 to -0.102) than the indirect effect of the intervention through marijuana use through marijuana use consequences to depression symptoms (B = -0.262, CI95 = -0.706 to -0.015). The findings from this study suggest that reductions in substance use and consequences of use may effectively reduce co-occurring depression symptoms. Furthermore, the findings highlight the efficacy of brief MI interventions in decreasing co-occurring depression symptoms in addition to substance use.

Copyright Status


Copyright Status