Background: Cannabis is available from medical dispensaries for treating posttraumatic stress disorder (PTSD) in many states of the union, yet its efficacy in treating PTSD symptoms remains uncertain.

Purpose: To identify ongoing studies and review existing evidence regarding the benefits and harms of plant-based cannabis preparations in treating PTSD in adults.

Data sources: MEDLINE, the Cochrane Library, and other sources from database inception to March 2017.

Study selection: English-language systematic reviews, trials, and observational studies with a control group that reported PTSD symptoms and adverse effects of plant-based cannabis use in adults with PTSD.

Data extraction: Study data extracted by 1 investigator was checked by a second reviewer; 2 reviewers independently assessed study quality, and the investigator group graded the overall strength of evidence by using standard criteria.

Data synthesis: Two systematic reviews, 3 observational studies, and no randomized trials were found. The systematic reviews reported insufficient evidence to draw conclusions about benefits and harms. The observational studies found that compared with nonuse, cannabis did not reduce PTSD symptoms. Studies had medium and high risk of bias, and overall evidence was judged insufficient. Two randomized trials and 6 other studies examining outcomes of cannabis use in patients with PTSD are ongoing and are expected to be completed within 3 years.

Limitation: Very scant evidence with medium to high risk of bias.

Conclusion: Evidence is insufficient to draw conclusions about the benefits and harms of plant-based cannabis preparations in patients with PTSD, but several ongoing studies may soon provide important results.

Primary funding source: U.S. Department of Veterans Affairs, Veterans Health Administration, Office of Research and Development, Quality Enhancement Research Initiative. (PROSPERO: CRD42016033623).