- Objectives: The objective this prospective, open-label study was to determine the long-term effect of medicinal cannabis treatment on pain and functional outcomes in subjects with treatment-resistant chronic pain. Methods: The primary outcome was change in pain symptom score on the STOPS (Treatment Outcomes in Pain Survey – Short Form) questionnaire at 6 months follow-up in intent-to-treat (ITT) population. The secondary outcomes included change in STOPS physical, social and emotional disability scales, pain severity and pain interference on brief pain inventory (BPI), sleep problems, and change in opioid consumption. Results: 274 subjects were approved for treatment; complete baseline data were available for 206 (ITT), and complete follow-up data for 176 subjects. At follow-up, pain symptom score improved from median 83.3 (95% CI 79.2-87.5) to 75.0 (95% CI 70.8-79.2), P<0.001. Pain severity score (7.50 [95% CI 6.75-7.75] to 6.25 [95% CI 5.75-6.75] and pain interference score (8.14 [95% CI 7.28-8.43] to 6.71 [95% CI 6.14-7.14]) improved (both P<0.001), together with most social and emotional disability scores. Opioid consumption at follow-up decreased by 44% (P<0.001). Serious adverse effects led to treatment discontinuation in two subjects. Discussion: The treatment of chronic pain with medicinal cannabis in this open-label, prospective cohort resulted in improved pain and functional outcomes, and significant reduction in opioid use. The results suggest long-term benefit of cannabis treatment in this group of patients, but the study's non-controlled nature should be considered when extrapolating the results.