The present investigation prospectively evaluated whether treatment changes in PTSD symptom severity, among military Veterans in residential PTSD treatment, were related to cannabis use 4 months after discharge from residential rehabilitation. The sample was comprised of 432 male military Veteran patients (Mage = 51.06 years, SD = 4.17), who had a primary diagnosis of PTSD and were admitted to a VA residential rehabilitation program for PTSD. Results demonstrated that lower levels of change in PCL-M scores between treatment intake and discharge were significantly predictive of greater frequency of cannabis use at 4-month follow-up (p < .05), even after accounting for the effects of length of treatment stay and frequency of cannabis use during the 2 months before treatment intake. Furthermore, post hoc analyses revealed that less change in PTSD avoidance/numbing and hyperarousal symptom severity during treatment was significantly predictive of a greater frequency of cannabis use at 4-month follow-up, after controlling for relevant covariates. Notably, these effects were specific to cannabis and were not found for the other substances examined among this sample, including alcohol and opiates. Implications of the findings are discussed with regard to the extant literature and future directions.
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