INVESTIGATOR: Barth Wilsey, M.D.
STUDY LOCATION: University of California, Davis
PROJECT TITLE: The Analgesic Effect of Vaporized Cannabis on Neuropathic Pain in Spinal Cord Injury
PROJECT TYPE: Clinical Study
We conducted a double-blind, placebo-controlled, crossover study evaluating the analgesic efficacy of vaporized cannabis in subjects, the majority of whom were experiencing neuropathic pain despite traditional treatment. Thirty-nine patients with central and peripheral neuropathic pain underwent a standardized procedure for inhaling medium-dose (3.53%), low-dose (1.29%), or placebo cannabis with the primary outcome being visual analog scale pain intensity. Psychoactive side effects and neuropsychological performance were also evaluated. Mixed-effects regression models demonstrated an analgesic response to vaporized cannabis. There was no significant difference between the 2 active dose groups’ results (P > .7). The number needed to treat (NNT) to achieve 30% pain reduction was 3.2 for placebo versus low-dose, 2.9 for placebo versus medium-dose, and 25 for medium- versus low-dose. As these NNTs are comparable to those of traditional neuropathic pain medications, cannabis has analgesic efficacy with the low dose being as effective a pain reliever as the medium dose. Psychoactive effects were minimal and well tolerated, and neuropsychological effects were of limited duration and readily reversible within 1 to 2 hours. Vaporized cannabis, even at low doses, may present an effective option for patients with treatment-resistant neuropathic pain.
The full results of this study have been published in the Journal of Pain.
The present study will be designed to evaluate the analgesic effects of vaporized cannabis in patients with neuropathic pain due to spinal cord injury. A within-subject crossover study of the effects of cannabis (3.5% and 1.7%) versus placebo on spontaneous and evoked pain will be performed. Both pain intensity and pain unpleasantness will be assessed to see if marijuana affects sensory-discriminative pain more or less than the motivational-affective component. If present, areas of mechanical allodynia will be assessed with repeated testing to determine the degree of the allodynia regression (if any) after inhaling cannabis via a vaporizer. Heat evoked pain will be studied using mild to moderately painful heat stimuli delivered to the painful area of the subject's body using an electronically controlled Peltier contact thermode via the Medoc TSA 2001 quantitative sensory tester. Neuropsychological functioning (attention, learning and memory, and psychomotor performance) will be evaluated with the Digit Symbol Modalities Test, the Hopkins Verbal Learning Test and the Grooved Pegboard Test before and after the administration of vaporized cannabis. The degree of antinociception will then be compared with neuropsychological effects of cannabis for a synopsis of the relative effectiveness (efficacy versus side-effects) of the doses employed.
The hypothesis will be that vaporized cannabis can induce dose dependent antinociceptive changes in spontaneous and evoked pain in subjects with neuropathic pain. The second hypothesis will be that the higher dose employed induce a greater degree of antinociception that is not independent of differences in mood, cognition and psychomotor performance. Finally, it is hypothesized that an interaction with time will occur such that antinociception will outlast changes in cognitive impairment and psychomotor performance.