The impact of substance use on posttraumatic stress disorder symptoms and treatment discontinuation.

This study examined the impact of ongoing substance use during posttraumatic stress disorder (PTSD) and substance use disorder (SUD) treatment on PTSD symptoms and treatment discontinuation. The study represents a secondary analysis of U.S. military veterans (N = 183) who participated in a randomized clinical trial for the treatment of both PTSD and SUD. Veterans mostly identified as Black (53.8%) or White (41.9%) and male (92.4%). Substance use, PTSD symptoms, and treatment discontinuation were measured at 4-week intervals throughout treatment. Predictors were the percentage of days with alcohol, cannabis, and other substance use (primarily cocaine and opioids) and the average number of alcoholic drinks per drinking day. Outcomes were PTSD symptoms and treatment discontinuation at concurrent and prospective assessments. Multilevel models accounted for the nested structure of the longitudinal data. Alcohol, cannabis, and other substance use did not predict PTSD symptoms or treatment discontinuation prospectively. Concurrently, we observed that as a participant's percentage of drinking days increased by 34.7% (i.e., 1 standard deviation), PTSD symptoms during the same period were 0.07 standard deviations higher (i.e., 1 point on the PCL), B = 0.03, p = .033. No other substances were related to PTSD symptoms concurrently. The findings demonstrate that PTSD symptoms improved regardless of substance use during exposure-based PTSD and SUD treatment, and treatment discontinuation was not associated with substance use. This study suggests that substance use during treatment cannot directly explain the poorer treatment outcomes observed in the literature on comorbid PTSD/SUD compared to PTSD-only populations.