Cancer-related pain affects about three in five cancer patients undergoing anti-cancer therapy and nine in 10 patients with advanced disease, according to the authors of this study. Previous research has found that cannabinoid use occurs in cancer patients, primarily to treat pain.
“The primary outcome in this systematic review was the absolute change in mean pain intensity, which is a more sensitive outcome than a dichotomous outcome, for example, proportion of participants who report a pain relief of 50% or greater from baseline to end of study. The aim was to determine the beneficial and adverse effects of cannabinoids compared with placebo or other active agents for the treatment of cancer-related pain in adults from RCTs [randomized controlled trials],” established the researchers, whose findings were published in BMJ Supportive & Palliative Care.
A search was performed using the following electronic databases: Embase (Ovid), Ovid MEDLINE(R) In-Process & Other Non-Indexed Citations, PsycINFO (Ovid), Conference Proceedings Citation Index–Science (Web Of Science; Thomson Reuters, New York City, NY), ClinicalTrials.gov (US NIH), ISRCTN registry (BMC), Cochrane Database of Systematic Reviews (Wiley), Cochrane Central Register of Controlled Trials (Wiley), and Database of Abstracts of Reviews of Effect (Wiley).
Eligible studies were RCTs that compared the effect of cannabinoids (THC:CBD, THC extract, nabiximols, Sativex, and medical cannabis) against placebo or other active agents to treat cancer-related pain in adult patients. The primary outcome of these studies was pain.
Exclusion criteria were studies that included patients undergoing surgery, healthy volunteers, or animals; were not RCTs; and did not have pain as the primary outcome.
The search yielded 2,805 studies; the systematic review included six RCTs encompassing 1,460 patients, and the meta-analysis included five studies encompassing 1,460 patients. All included RCTs had a low bias risk. The average Numeric Rating Scale pain scores did not largely differ between patients taking cannabinoids versus placebo (mean difference, –0.21; 95% confidence interval [CI], –0.48 to 0.07; P=0.14). This finding persisted even when only assessing phase III studies in the meta-analysis (mean difference, –0.02; 95% CI, –0.21 to 0.16; P=0.80). Cannabinoids were associated with a greater risk of adverse events than placebo: somnolence (odds ratio [OR]=2.69; 95% CI, 1.54–4.71; P<0.001) and dizziness (OR=1.58; 95% CI, 0.99–2.51; P=0.05).
The authors summarized: “For a medication to be useful, there needs to be a net overall benefit, with the positive effects (analgesia) outweighing adverse effects. None of the included phase III studies show benefit of cannabinoids. One of the phase II studies showed benefit in their primary outcome; the other was negative in its primary outcome, although a secondary outcome was positive. When statistically pooled, there was no decrease in pain score from cannabinoids. There are, however, significant adverse effects and dropouts reported from cannabinoids. Based on evidence with a low risk of bias, cannabinoids cannot be recommended for the treatment of cancer-related pain.”