Posttraumatic stress disorder (PTSD) represents one of the most common mental health disorders, particularly among veterans, and is associated with significant distress and impairment. This highly debilitating disorder is further complicated by common comorbid psychiatric disorders, such as substance use disorders (SUD). Individuals with PTSD and co-occurring SUD also commonly present with secondary symptoms, such as elevated depression. Little is known, however, about how these secondary symptoms are related to treatment outcome. The aim of the present study, therefore, was to examine (1) the effects of treatment of comorbid PTSD/SUD on depressive symptoms; and (2) whether this effect was mediated by changes in PTSD severity or changes in SUD severity. Participants were 81 U.S. military veterans (90.1% male) with PTSD and SUD enrolled in a randomized controlled trial examining the efficacy of an integrated, exposure-based treatment (Concurrent Treatment of PTSD and Substance Use Disorders Using Prolonged Exposure
= 54) versus relapse prevention (n
= 27). Results revealed significantly lower depressive symptoms at post-treatment in the COPE group, as compared to the relapse prevention group. Examination of the mechanisms associated with change in depression revealed that reduction in PTSD severity, but not substance use severity, mediated the association between the treatment group and post-treatment depression. The findings underscore the importance of treating PTSD symptoms in order to help reduce co-occurring symptoms of depression in individuals with PTSD/SUD. Clinical implications and avenues for future research are discussed.
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