Introduction:

Retrospective studies and patient surveys investigating cannabis-based products for endometriosis have suggested potential benefits, highlighting the unmet need for effective therapeutic alternatives. This study evaluated the efficacy of cannabidiol in reducing pain among women with surgically treated endometriosis who experienced symptom recurrence.

Materials and Methods:

This was a single-centre, randomised, parallel, triple-blind, placebo-controlled trial. Eligible participants were women with surgically confirmed endometriosis, previously treated surgically, receiving hormonal therapy, and reporting symptom recurrence. A total of 102 participants were randomized (1:1) into two groups, with 51 allocated to oral cannabidiol-enriched oil (CBDO) and 51 allocated to placebo. The intervention lasted 10 weeks. The oil was administered twice daily with dose escalation from 10 mg/day (week 1) to 150 mg/day (week 9), followed by tapering. The study was terminated after the planned interim analysis due to a lack of difference in the primary outcome and a higher frequency of adverse events in the CBDO group. Primary outcomes were changes in pain intensity (Visual Analogue Scale) and the proportion of participants with ≥30% and ≥50% pain reduction. Participants reported their average perceived pain intensity during the preceding week at each visit. Secondary outcomes included sensory thresholds, psychiatric symptoms, functional impairment, quality of life (QoL), and adverse effects, focusing on common cannabidiol-related symptoms.

Results:

Approximately 40% of participants in both groups achieved ≥50% pain reduction, and ∼60% reported ≥30% improvement. At the end of treatment, mean pain intensity was 41.6 mm in the CBDO group and 36.8 mm in the placebo group. Although both groups showed significant within-group reductions, differences between groups were not significant. CBDO was associated with improvements in psychological symptoms and several QoL domains but also with more mild adverse events, mainly gastrointestinal symptoms and perceived weight changes. Participants in the placebo group exhibited better scores in physical QoL domains. No serious adverse events occurred.

Discussion:

Both groups showed consistent and significant pain reduction, but cannabidiol was not superior to placebo. The trial was discontinued at the interim analysis due to the absence of clinically relevant benefit and higher mild adverse-event rates with CBDO. Improvements in placebo-treated participants highlight potential placebo effects and the limited power of secondary analyses.