Cannabis use has become more common in the United States—the number of persons reporting past-year cannabis use nearly doubled between 2001 and 2013 to 1 in 10 adults (1). Cannabis has been legalized for recreational purposes in 8 states of the union and the District of Columbia and for medical use in 28 states and the District of Columbia (2–4). Many states list posttraumatic stress disorder (PTSD) as an indication for cannabis use (5). More than one-third of patients seeking cannabis for medical purposes in states where it is legal list PTSD as the primary reason for their request (6–8). However, little comprehensive and critically appraised information is available about the benefits and harms of cannabis use for treating PTSD. The objectives of this systematic review were to assess the benefits and harms of plant-based cannabis use in patients with PTSD and to identify ongoing studies in this area.