Smoked cannabis for chronic neuropathic pain: a randomized controlled trial

CMAJ • October 5, 2010; 182 (14). First published August 30, 2010; doi:10.1503/cmaj.091414
© 2010 Canadian Medical Association or its licensors

Mark A. Ware, MBBS, Tongtong Wang, PhD, Stan Shapiro, PhD,Ann Robinson, RN, Thierry Ducruet, MSc, Thao Huynh, MD, Ann Gamsa, PhD,Gary J. Bennett, PhD and Jean-Paul Collet, MD PhD

From the Department of Anesthesia (Ware), the Department of Family Medicine (Ware), the Department of Epidemiology, Biostatistics and Occupational Health (Wang, Shapiro), the Department of Medicine (Huynh) and the Alan Edwards Centre for Research on Pain (Gamsa, Bennett), McGill University, Montréal, Que.; Boreal Primum (Robinson, Ducruet), Montréal, Que.; and the Centre for Applied Health Research and Evaluation (Collet), University of British Columbia, Vancouver, BC

Correspondence to: Dr. Mark A. Ware, E19.145, Montréal General Hospital, 1650 Cedar Ave., Montréal QC H3G 1A4; mark.ware@muhc.mcgill.ca

Background: Chronic neuropathic pain affects 1%–2% of the adult population and is often refractory to standard pharmacologic treatment. Patients with chronic pain have reported using smoked cannabis to relieve pain, improve sleep and improve mood.

Methods: Adults with post-traumatic or postsurgical neuropathic pain were randomly assigned to receive cannabis at four potencies (0%, 2.5%, 6% and 9.4% tetrahydrocannabinol) over four 14-day periods in a crossover trial. Participants inhaled a single 25-mg dose through a pipe three times daily for the first five days in each cycle, followed by a nine-day washout period. Daily average pain intensity was measured using an 11-point numeric rating scale. We recorded effects on mood, sleep and quality of life, as well as adverse events.

Results: We recruited 23 participants (mean age 45.4 [standard deviation 12.3] years, 12 women [52%]), of whom 21 completed the trial. The average daily pain intensity, measured on the 11-point numeric rating scale, was lower on the prespecified primary contrast of 9.4% v. 0% tetrahydrocannabinol (5.4 v. 6.1, respectively; difference = 0.7, 95% confidence interval [CI] 0.02–1.4). Preparations with intermediate potency yielded intermediate but nonsignificant degrees of relief. Participants receiving 9.4% tetrahydrocannabinol reported improved abilityto fall asleep (easier, p = 0.001; faster, p < 0.001; more drowsy, p = 0.003) and improved quality of sleep (less wakefulness, p = 0.01) relative to 0% tetrahydrocannabinol. We found no differences in mood or quality of life. The most common drug-related adverse events during the period when participants received 9.4% tetrahydrocannabinol were headache, dry eyes, burning sensation in areas of neuropathic pain, dizziness, numbness and cough.

Conclusion: A single inhalation of 25 mg of 9.4% tetrahydrocannabinol herbal cannabis three times daily for five days reduced the intensity of pain, improved sleep and was well tolerated. Further long-term safety and efficacy studies are indicated. (International Standard Randomised Controlled Trial Register no. ISRCTN68314063)