The proposed CDA-2 will include a randomized control trial to evaluate the efficacy of using Cannabidiol (CBD), a non-intoxicating phytocannabinoid, as an adjunctive to exposure therapy. The trial will compare PE+CBD to PE+placebo in a sample of 136 Veterans with PTSD at the VASDHS. The rationale for the proposed RCT is informed by neurobiological, preclinical, and clinical research on PTSD and cannabinoids. The study represents the logical and innovative next step for augmenting existing treatments and developing novel pharmacotherapy for PTSD. Moreover, the proposal: 1) aligns with the VA's patient care mission in its aim to improve treatment for Veterans with PTSD, 2) directly addresses the VA's PTSD Psychopharmacology Initiative, and 3) addresses an area of research that has largely been ignored by VA but is of direct relevance to multiple VA stakeholders (i.e., investigating the efficacy of cannabinoid treatments). Findings from the proposed RCT will inform clinical practice and policy by investigating whether administration of CBD in the context of PE therapy will improve treatment outcomes for Veterans with PTSD. The proposed CDA-2 will provide the candidate with an important training opportunity to merge her primary research interests (cannabinoid therapeutics and PTSD RCTs) and to develop specialized skill in RCT execution that involves both behavioral and novel psychopharmacology. The candidate will be mentored by leading experts who specialize in: PTSD treatment, psychopharmacology, RCT design, cannabinoid administration trials, and biostatistics. The proposed work will be conducted within a leading VA research center (VASDHS) and world-renowned research institution (UCSD School of Medicine). The proposed trial will also allow the candidate necessary training for achievement of her long-term goal to become an independent researcher within VA. Scaffolded training and mentorship in RCT design, cannabinoid psychopharmacology, biostatistics and grant writing will help propel the candidate to independence in a cutting-edge research area. Finally, results of the trial will lay the groundwork for future implementation studies that would attempt to determine feasibility of use of CBD across VA clinics and determine whether implementation leads to reduced sessions of PE, greater patient and therapist satisfaction, and lower costs to VA.