The trial will include a randomized control trial to evaluate the efficacy of using Cannabidiol (CBD), a non-intoxicating cannabinoid, as an adjunctive to Prolonged Exposure therapy (PE). The trial will compare PE + CBD to PE + placebo in a sample of 136 military Veterans with PTSD at the VA San Diego Medical Center. The study represents the logical and innovative next step for augmenting existing treatments and developing novel pharmacotherapy for PTSD. 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 military Veterans with PTSD.