Adding medical cannabis to standard analgesic treatment for fibromyalgia: a prospective observational study

OBJECTIVES: To assess any clinical improvement attributable to the addition of medical cannabis treatment (MCT) to the stable (>3 months) standard analgesic treatment of fibromyalgia (FM) patients, the retention rate and any changes in the concomitant analgesic treatment over a period of six months. METHODS: The study involved 102 consecutive FM patients with VAS scores ≥4 despite standard analgesic treatment. Patients were prescribed two oil-diluted cannabis extracts: Bedrocan (22% THC, <1% CBD), and Bediol (6.3% THC, 8% CBD). FM severity was periodically assessed using Fibromyalgia Impact Questionnaire (FIQR), Fibromyalgia Assessment Scale (FAS), FACIT-Fatigue score, Pittsburgh Sleep Quality Index (PSQI), and Zung Depression and Anxiety Scales. During the study, patients were allowed to reduce or stop their concomitant analgesic therapy. RESULTS: The 6-month retention rate was 64%. A significant improvement in the PSQI and FIQR was observed in respectively 44% and 33% of patients. 50% showed a moderate improvement in the anxiety and depression scales. Multiple regression analysis showed a correlation between the body mass index (BMI) and FIQR improvement (p=0.017). Concomitant analgesic treatment was reduced or suspended in 47% of the patients. One-third experienced mild adverse events, which did not cause any significant treatment modifications. CONCLUSIONS: This observational study shows that adjunctive MCT offers a possible clinical advantage in FM patients, especially in those with sleep dysfunctions. The clinical improvement inversely correlated with BMI. The retention rate and changes in concomitant analgesic therapy reflect MCT efficacy of the improved quality of life of patients. Further studies are needed to confirm these data, identify MCT-responsive sub-groups of FM patients, and establish the most appropriate posology and duration of the therapy.