The effectiveness of cannabis-based products for chronic neuropathic pain is not supported by high-quality evidence, according to a study published in Cochrane Database of Systematic Reviews. In addition, any potential benefits of cannabis-based medicines for treatment of the condition might be outweighed by associated nervous system adverse events and psychiatric disorders.
Three investigators conducted a review of 16 randomized double-blind controlled studies, 2 to 26 weeks long, involving 1750 adult participants, to assess the efficacy, safety, and tolerability of cannabis-based medicines for neuropathic pain compared with placebo.
They also examined each study for quality level and risk for bias. The studies included in this review evaluated a variety of cannabis-based medicines such as herbal cannabis as well as sprays and tablets containing either synthetic or plant-derived active cannabis ingredients.
Reviewers rated quality of evidence for each study based on the associated number of “unclear or high risks of bias judgments”: low (6-8; 2 studies), moderate (3-5; 12 studies), and high (0-2; 2 studies).
Cannabis (at any dose) was found to provide ≥50% pain relief to a greater percentage of individuals compared with placebo (21% vs 17%, respectively; risk difference [RD], 0.05; 95% CI, 0.00-0.09). Evidence for improvement — assessed with the Patient Global Impression of Change — was 26% with cannabis vs 21% with placebo (RD, 0.09; 95% CI, 0.01-0.17; very low quality evidence). Tolerability was comparable for cannabis and placebo (very low quality evidence).
More study participants dropped out because of adverse events with cannabis-based medicines (10%) than with placebo (5%; RD, 0.04; 95% CI, 0.02-0.07).
In addition, nervous system adverse events and psychiatric disorders may affect a greater percentage of people taking cannabis-based medicines compared with placebo (nervous system adverse events: 61% vs 29%, respectively; RD, 0.38; 95% CI, 0.18-0.58; 9 studies; low-quality evidence; psychiatric disorders: 17% vs 5%, respectively; RD, 0.10; 95% CI, 0.06-0.15; 9 studies; low-quality evidence).
“Since relatively few participants achieve a worthwhile response with cannabis-based medicines, decisions to use these medicines may require stopping rules to avoid the unnecessary exposure to harms in the absence of benefit,” concluded the review authors.
Mücke M, Phillips T, Radbruch L, Petzke F, Häuser W. Cannabis-based medicines for chronic neuropathic pain in adults. Cochrane Database Syst Rev. 2018;3:CD012182.