Limited Evidence to Support Cannabis Use for Chronic Pain

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.

One comment

  1. Even as a pain management specialist it is challenging to differentiate neuropathic induced pain from other types of chronic pain. Neuropathy just means that nerves are sick and not working properly. Causes for same or quite numerous and challenging to rule out even in cancer patients. Granted, cancer pain is relatively unique in terms of chronic pain because it reflects ongoing and worsening noci-ception. I’m not sure of the mechanism for increased pain in M.S. but I would suggest it is rather special compared to the large bulk of patients with Chronic Pain.

    I think the findings, to the contrary, particularly when compared to other agents used regularly for chronic pain are not limited but rather impressive. I find cannabis is particularly effective in subgroups of patients with PTSD history. I would recommend that all studies looking at cannabis for pain would evaluate subgroups with higher past trauma scores.
    Also, as to increase risks of MVA accidents in those who used cannabis, based on biases and prejudices that are rampant, I would want some reassurance that other confounding variables were well looked at. Just because cannabis is in the urine or was recently used doesn’t mean it is the source of impairment or cause of the MVA. Of all agents that might cause impairment it lingers longer than most in the urine and other body tissues.

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