Cannabidiol versus placebo in patients with fibromyalgia: a randomised, double-blind, placebo-controlled, parallel-group, single-centre trial.

Objectives: Cannabidiol (CBD) is used to alleviate fibromyalgia pain despite limited evidence for efficacy. This study assessed the efficacy and safety of CBD vs placebo in patients with fibromyalgia, hypothesising that CBD would be superior to placebo in reducing pain. Methods: In this single-centre, double-blind, randomised, placebo-controlled trial, patients diagnosed with fibromyalgia were recruited from a specialised outpatient clinic in Denmark. Eligible participants were randomised 1:1 and stratified by sex, defined as biological sex assigned at birth based on physical anatomy. Age (<45 vs >/=45), and pain level (<7 vs >/=7) on a 0 to 10 numeric rating scale (NRS) to receive 50 mg plant-derived CBD or placebo tablets. The primary outcome was change in pain intensity at week 24, assessed on the NRS pain subitem in the revised Fibromyalgia Impact Questionnaire in the intention-to-treat population. Adverse events were monitored throughout the study in the safety population. Results: Of 273 participants screened for eligibility, 200 were included and randomised to receive CBD (n = 100) or placebo (n = 100). At week 24, mean change in pain intensity was -0.4 points (95% CI: -0.82 to 0.08) in the CBD group and -1.1 points (95% CI: -1.53 to -0.63) in the placebo group, corresponding to a between-group difference of -0.7 points (95% CI: -1.2 to -0.25; P = .0028) favouring placebo. Adverse events were generally mild and evenly distributed between groups. Conclusions: The findings do not support CBD 50 mg daily as an analgesic supplement for patients with fibromyalgia. Clinicaltrials: gov number: NCT04729179.