Although legal and illicit cannabis is frequently used for chronic pain control, the strength of scientific evidence for this practice is uncertain. Researchers examined 2 systematic reviews, 27 randomized controlled trials, and 3 observational studies to assess the impact of cannabis on chronic pain. Eleven systematic reviews and 32 observational studies were identified to assess adverse effects.
- For chronic neuropathic pain, 11 studies indicated that “a higher proportion of intervention patients had clinically significant pain relief up to several months later.” A meta-analysis of 9 of these studies indicated patients receiving cannabis were more likely to report 30% or better neuropathic pain improvement than control patients (risk ratio [RR], 1.43).
- For chronic pain due to multiple sclerosis (9 studies), cancer (3 studies), and other causes (5 studies), there was insufficient evidence to show a benefit of cannabis.
- For adverse effects, there was moderate evidence to suggest an increased risk of motor vehicle accidents and limited evidence to suggest increased mental health adverse effects from cannabis use.
Comments: This well-done systematic review indicates that cannabis may be effective for chronic neuropathic pain. Conclusions about its efficacy for other types of chronic pain could not be drawn, illustrating the inadequate evidence base for cannabis as a treatment for chronic pain. Most identified studies included few or highly selected participants, were short duration, and used variable cannabinoid dose. Higher quality studies are needed and will either need to use standardized plant-based cannabis or study specific doses of cannabinoids. For this to happen in the US, federal barriers to cannabis-related research will need to be relaxed.
Kevin L. Kraemer, MD, MSc
Reference: Nugent SM, Morasco BJ, O’Neil ME, et al. The effects of cannabis among adults with chronic pain and an overview of general harms: a systematic review. Ann Intern Med. 2017;167(5):319–331.