• Elaine G Boland, Michael I Bennett, Victoria Allgar, and Jason W Boland.
• Hull University Teaching Hospitals NHS Trust, Cottingham, UK.
• BMJ Support Palliat Care. 2020 Mar 1; 10 (1): 14-24.

ObjectivesThere is increased interest in cannabinoids for cancer pain management and legislative changes are in progress in many countries. This study aims to determine the beneficial and adverse effects of cannabis/cannabinoids compared with placebo/other active agents for the treatment of cancer-related pain in adults.MethodsSystematic review and meta-analysis to identify randomised controlled trials of cannabinoids compared with placebo/other active agents for the treatment of cancer-related pain in adults to determine the effect on pain intensity (primary outcome) and adverse effects, including dropouts. Searches included Embase, MEDLINE, PsycINFO, Web of Science, ClinicalTrials.gov, Cochrane and grey literature. Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed.ResultsWe identified 2805 unique records, of which six randomised controlled trials were included in this systematic review (n=1460 participants). Five studies were included in the meta-analysis (1442 participants). All had a low risk of bias. There was no difference between cannabinoids and placebo for the difference in the change in average Numeric Rating Scale pain scores (mean difference -0.21 (-0.48 to 0.07, p=0.14)); this remained when only phase III studies were meta-analysed: mean difference -0.02 (-0.21 to 0.16, p=0.80). Cannabinoids had a higher risk of adverse events when compared with placebo, especially somnolence (OR 2.69 (1.54 to 4.71), p<0.001) and dizziness (OR 1.58 (0.99 to 2.51), p=0.05). No treatment-related deaths were reported. Dropouts and mortality rates were high.ConclusionsStudies with a low risk of bias showed that for adults with advanced cancer, the addition of cannabinoids to opioids did not reduce cancer pain.Trial Registration NumberCRD42018107662.© Author(s) (or their employer(s)) 2020. No commercial re-use. See rights and permissions. Published by BMJ.

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