Systematic Review and Meta-analysis Seem to Indicate that Cannabinoids for Chronic Primary Pain Treatment Have Limited Benefit

Introduction: The IASP ICD-11 chronic primary pain (CPP) definition includes 19 different painful conditions. In recent years, interest in the potential role of cannabinoids in the management of CPP has increased, since they demonstrated a possible efficacy in treating pain, especially in secondary pain conditions. However, limited evidence is available for patients with CPP. The aim of this systematic review and meta-analysis is to evaluate the efficacy and safety of cannabinoid administration in CPP.

Methods: PubMed, EMBASE, and Cochrane Library were searched form the beginning up to 31 October 2021 to retrieve published articles of randomized controlled trials (RCTs) or observational, retrospective or prospective, studies, investigating cannabinoids in CPP. The study screening process was completed during November 2021. The primary outcome was pain reduction by means of the visual analogue scale (VAS). Secondary outcomes were quality of life by means of the fibromyalgia impact questionnaire (FIQ) or other available scales, appetite, anxiety, depression, and sleep by means of any available scales. Safety was assessed with the reporting of serious adverse events (SAE) and discontinuation due to adverse events. Risk of bias was assessed. The weighted generic inverse variance method and Mantel-Haenszel method were used to estimate the mean difference (MD) and odds ratios (OR) with 95% confidence intervals (CI) for continuous and dichotomous outcomes, respectively. For outcome measures reported with different scales (pain, anxiety, depression), we used the standardized MD (SMD) as the effect measure and then converted it into units of the VAS scale for pain, the Beck Anxiety Inventory (BAI) for anxiety, and the Beck Depression Inventory (BDI) for depression. Summary of findings was produced using GRADEproGDT.

Results: From 3007 identified records, we included eight articles reporting the results of eight different RCTs (four parallel and four crossover studies; seven compared to placebo and one to amitriptyline), with a total population of 240 patients. VAS pain reduction was non-significant for cannabinoids against placebo (MD = - 0.64; 95% CI - 1.30 to 0.02) or amitriptyline (MD = - 0.19; 95% CI - 0.58 to 0.19). More than 4 weeks cannabinoid treatment significantly reduced pain compared to placebo in parallel studies with more than 4 weeks of treatment duration (MD = - 1.28; 95% CI - 2.33 to - 0.22). Differences for the FIQ (MD = - 21.69; 95% CI - 46.20 to 2.82), BAI (MD = - 2.32; 95% CI - 7.99 to 3.08), and BDI (MD = 2.32; 95% CI - 1.71 to 6.35) were non-significant, likewise for discontinuation due to adverse events (OR = 2.15; 95% CI 0.44-10.65), when comparing cannabinoids to placebo. The quality of the evidence was generally low mainly as a result of imprecision and risk of bias.

Conclusion: Cannabinoid treatment in patients with CPP had limited benefit on pain relief; however, it might improve pain with long-term administration.