Challenges in conducting a feasibility randomized controlled trial of medicinal cannabis for endometriosis pain in Australia

Background and purpose: People with endometriosis report consuming cannabis to manage their endometriosis symptoms, however, its efficacy has not been established in clinical studies. This study aimed to determine the feasibility, acceptability, and safety of two different medicinal cannabis interventions against placebo in people with endometriosis. Materials and methods: A three-armed randomised controlled trial was conducted, comparing the effects of using both inhaled medicinal cannabis using dried flower containing 16 % delta-9-tetrahydrocannabinol (THC) via vaporisation and an oral oil containing 100mg cannabidiol (CBD) per mL together, versus an oral CBD oil alone, versus a taste- and colour-matched placebo oil. The trial aimed to recruit 63 participants (21 per intervention group). Outcome measures included safety and the occurrence of adverse events, and the acceptability and feasibility of recruitment and retention. Results: Overall, 12 participants were randomised to one of three groups, of whom seven withdrew from the study; four completed the study and one was lost to follow-up. Therefore, acceptability and feasibility of recruitment and retention was considered low. There were 10 adverse events reported (two unrelated to cannabis and eight possibly related to cannabis) and two serious adverse events reported (both unrelated to the intervention). Conclusion: Despite an urgent need for an evidence-based approach to using cannabis for endometriosis-related pain, our feasibility trial failed to recruit and retain the small intended sample. Failure of the trial was largely driven by two factors: the requirement to abstain from driving, and a high level of participant withdrawal.