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 7.0% delta-9-THC) 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 a 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, the Grooved Pegboard Test Trail Making Test and the Paced Auditory Serial Addition Test (PASAT) before and after the administration of vaporized cannabis. Emotional responses will be evaluated using the Profile of Moods States. The degree of antinociception will then be compared with neuropsychological and mood effects of cannabis for a synopsis of the relative effectiveness (i.e., efficacy versus side-effects) of the doses employed. The major hypothesis will be that vaporized cannabis can induce antinociceptive changes in spontaneous and evoked pain in subjects with neuropathic pain. The second hypothesis will be that the higher dose of cannabis (7.0%) employed will induce the same or a greater degree of antinociception that is not independent of differences in mood, cognition, and psychomotor performance.
This study will demonstrate that vaporized marijuana results in antinociception when compared to placebo in subjects with spinal cord injury. To further evaluate potential benefits and side effects, the effect of different strengths of cannabis on mood, cognition and psychomotor performance will also be measured.
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