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).

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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.

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Reference

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.