The use of medical marijuana to treat patients with treatment-resistant Post-Traumatic Stress Disorder (PTSD) is supported by a number of sources, including research in lab animals, fMRI imaging in humans, and anecdotal reports from countless health practitioners and patients. Additionally, clinical research in Israel evaluating medical marijuana as treatment for PTSD has been promising. This study will test four strains of smoked marijuana, each containing different concentrations of active cannabinoids, in two three-week stages, as a pharmacological agent to manage PTSD symptoms among 80 American war veterans. This study is a collaboration between me and researchers from Johns Hopkins University, University of Colorado, and University of Pennsylvania. This will be the first randomized controlled crossover clinical trial in the United States testing the therapeutic potential of marijuana for PTSD. The primary measured outcome will be the Clinician Administered PTSD Scale (CAPS-5), alongside extensive secondary outcomes including sleep patterns, depression, withdrawal symptoms, metabolic and inflammation panels, and self-reporting by the patients.