Systematic Review: Effects of Cannabis among Adults with Chronic Pain, Including General Harms
The use of cannabis for medicinal purposes has become increasingly accepted in the U.S.; moreover, 45-80% of individuals who seek state-sanctioned cannabis for medical purposes do so for pain management. Among patients who are prescribed long-term opioid therapy for pain, up to 39% also use cannabis. This systematic review assesses the efficacy of cannabis for treating chronic pain, and provides a broad overview of the short- and long-term physical and mental health effects of cannabis use in chronic pain and general patient populations. 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) from database inception through February 2016, and in March 2017 updated the search with any new randomized controlled trials and systematic reviews. After reviewing 13,674 titles and abstracts, they identified 13 systematic reviews and 62 primary studies that were relevant to their analysis.
- Overall, investigators found low-strength evidence that cannabis may improve pain in some patients with neuropathic pain. Studies generally did not find clinically significant differences on continuous pain scales between groups, but a higher proportion of intervention patients experienced clinically significant pain relief at up to several months of follow-up.
- Overall, insufficient evidence was found to characterize the effects of cannabis on pain in patients with multiple sclerosis due to too few methodologically rigorous studies, inconsistent findings across studies, a lack of long-term outcomes, and small numbers of patients included in the trials.
- Moderate-strength evidence suggests that light to moderate cannabis smoking does not adversely impact lung function over about 20 years. However, the limited evidence examining the effects of heavy use suggests a possible deleterious effect on lung function over time.
- There is a consistent association between cannabis use and the development of psychotic symptoms over the short and long term. There is moderate-strength evidence that cannabis intoxication is associated with an increased risk of being involved in a motor vehicle accident.
- Cannabis appears to be associated with at least small, short-term deleterious effects on cognition in active users, but long-term effects in past users are uncertain.
- There is virtually no conclusive information about the benefits of cannabis in chronic pain populations and limited information on harms, so methodologically strong research in almost any area of inquiry is likely to add to the strength of evidence.
- This review focused specifically on pain outcomes in patients, but the authors acknowledge other outcomes (i.e. sleep, mood) also are important to consider in the treatment of chronic pain.
This study was funded by VA HSR&D's Quality Enhancement Research Initiative (QUERI). Dr. Kansagara is part of QUERI's Evidence-Based Synthesis Program Center, Portland, OR.
Nugent S, Morasco B, O’Neil M, et al. The Effects of Cannabis among Adults with Chronic Pain and an Overview of General Harms: A Systematic Review. Annals of Internal Medicine. September 5, 2017;167(5):319-31.