The report is a product of the VA/HSR Evidence Synthesis Program.

Benefits and Harms of Cannabis in Chronic Pain or PTSD: A Systematic Review

Recent studies suggest that from 45% to 80% of individuals who seek cannabis for medical purposes do so for pain management, and an estimated 6% to 39% of patients who are prescribed opioid medication for pain also use cannabis. In addition, more than one-third of patients seeking cannabis for medical purposes cite post-traumatic stress disorder (PTSD) as the primary reason for the request. Approximately 15% of Veterans who are treated in VA outpatient PTSD clinics report recent (past six months) cannabis use. Thus, given the social, political, and legal changes surrounding cannabis use, physicians in both VA and non-VA settings will increasingly need to engage in evidence-informed discussions about the potential benefits and harms of cannabis use with their patients.

This systematic review sought to assess the effectiveness of plant-based cannabis preparations in treating chronic pain or PTSD. In addition, investigators sought to:

• Assess the impact of short- and long-term cannabis use on the risk of adverse effects such as pulmonary diseases, cardiovascular diseases, cancer, and psychosis;
• Provide a broad overview of more recently recognized "emerging harms" of cannabis use; and
• Identify important areas of ongoing research and evidence gaps.

Investigators with VA's Evidence-based Synthesis Program Center located in Portland, OR searched multiple data sources (i.e., MEDLINE, Embase, PubMed) and grey literature (outside traditional publishing channels) sources from database inception through February 2016. After reviewing 10,875 titles and abstracts, they identified 12 systematic studies and 48 primary studies that were relevant to their analysis.

Summary of Review
Although cannabis is increasingly available for medical and recreational use, there is little methodologically rigorous evidence examining its effects in patients with chronic pain or PTSD.

Treatment of chronic pain
There is limited evidence that cannabis may improve pain, spasticity, and sleep in select populations with multiple sclerosis. Most of these studies used cannabis preparations in which the concentration of active ingredients (tetrahydrocannabinol and cannabidiol) was precisely defined. Given the paucity of high-quality trials and the poor applicability of studies to current general medical practice, the evidence is insufficient to determine the effects in other chronic pain populations. There is insufficient evidence to determine the effects on quality of life or mental health outcomes in any chronic pain population.

Treatment of PTSD
The investigators of this systematic review found no trials examining the effects of cannabis in PTSD populations, and there was insufficient evidence from observational studies to draw conclusions about its effectiveness in patients with PTSD.

Harms
In younger populations, light to moderate cannabis use does not appear to be associated with adverse pulmonary effects over the long-term, but pulmonary effects have not been studied in older populations or individuals with comorbid medical conditions. There is limited and inconsistent evidence examining the effects of cannabis use on the risk of various types of cancer. There is consistent evidence that suggests an association between cannabis use and psychotic symptoms, as well as cognitive impairment in active users in general populations, though there is limited evidence specific to patients with chronic pain or PTSD. There are a number of adverse effects that appear to be related to cannabis use and may be important for clinicians to be familiar with, but whose incidence has not been well characterized. Adverse effects include infectious disease complications, cannabis hyperemesis syndrome, and violent behavior.

Evidence gaps and ongoing research
There is no conclusive information about the benefits of cannabis in chronic pain or PTSD populations and limited information about its harms, so methodologically strong research in almost any area of inquiry is likely to add to the strength of evidence.

The authors identified 10 ongoing clinical trials examining the effectiveness of cannabis for a variety of chronic pain populations including patients with neuropathic pain, cancer, osteoarthritis, sickle cell disease, low back pain, and ulcerative colitis. There are also two trials examining the benefits and harms of cannabis for PTSD that should add to the body of evidence.

A cyberseminar session titled "Benefits and Harms of Cannabis in Chronic Pain or Post-Traumatic Stress Disorder: A Systematic Review" will be held on Monday, March 20, 2017 from 1:00pm to 2:00pm (ET). To register, go to the HSR&D Cyberseminar web page.

Reference
Kansagara D, O'Neil M, Nugent S, Freeman M, Low A, Kondo K, Elven C, Zakher B, Motu'apuaka M, Paynter R, Morasco BJ. Benefits and Harms of Cannabis in Chronic Pain or Post-Traumatic Stress Disorder: A Systematic Review. VA ESP Project #05-225; 2016.

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This report is a product of VA/HSR&D's Quality Enhancement Research Initiative's (QUERI) Evidence-Based Synthesis Program (ESP), which was established to provide timely and accurate synthesis of targeted healthcare topics of particular importance to VA managers and policymakers – and to disseminate these reports throughout VA.

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