As of June 1, 2017, a total of 18 of 76 participants have enrolled and received study drug in the first-ever clinical trial of smoked marijuana (cannabis) for posttraumatic stress disorder (PTSD) in U.S. veterans. Four new participants have enrolled since May 4, and participant screening is ongoing. Taking place at the Scottsdale Research Institute (SRI) in Phoenix, Arizona, this clinical trial will evaluate the safety and efficacy of four different potencies of marijuana for symptoms of PTSD in 76 U.S. veterans.