In a randomized, placebo-controlled human trial published in the Journal of Pain, researchers investigated the use of vaporized cannabis for neuropathic pain (NeP) in patients with spinal cord injury (SCI) or disease.
NeP in SCI patients may result from altered sensory processing due to the injury. Though pregabalin was approved in 2012 for the treatment of SCI-related NeP pain, the “number needed to treat (NNT) for 50% pain relief (7.1 (95% confidence interval 3.9–37)) was higher than in most peripheral neuropathic pain studies,” wrote the authors of the new study. Opioids carry the risk of dependence and are often discontinued due to side effects, according to one patient survey. Only half of those respondents who tried gabapentin continued to use it, and those who tried it reported only moderate pain relief. Clearly, there remains a need for additional pain-relief options for SCI patients, for whom NeP adds to the already large burden they suffer from impaired functioning.
“Modulation of glial cell activation and blockade of signaling pathways between neuronal and non-neuronal cells offers new opportunities for more effective treatment of neuropathic pain,” the authors explained. “Given the need for therapeutic advancement, it is surprising that few clinical studies have examined drugs altering glial function” such as cannabinoids, which have been shown to have analgesic effects for NeP in multiple trials.
In three 8-hour laboratory experiments, researchers from the Davis and San Diego campuses of the University of California tested the analgesic effects of vaporized cannabis in 42 patients with spinal cord injury or disease whose NeP pain persisted despite conventional treatment. Patients with certain psychological and medical comorbidities were excluded. Using standardized procedures on each occasion, the patients were administered 4 inhalations containing placebo or vaporized cannabis with a concentration of either 2.9% or 6.7% delta-9-tetrahydrocannabinol. In a second dosing 3 hours later, participants were given the choice to inhale 4 to 8 puffs; by using flexible dosing, the researchers hoped to reduce the placebo effect. The primary outcome was patients’ scoring on an 11-point numerical pain intensity rating scale.
The results show that vaporized cannabis had a significant analgesic response over placebo (P <.05), with no difference in analgesic potency observed between the two active doses (P >.11). The percentage of patients whose pain was reduced by 30% or more was 45% for placebo (95% confidence interval [CI]: 31-60%), 70% for the lower dose of cannabis (95% CI: 54-83%), and 88% (95% CI: 74-95%) for the higher dose. The effects remained even after controlling for the effects of subjective and psychoactive side effects – for example, the indication of a “good drug effect” and “feeling high”–which were found to be dose-dependent. Due to disabilities in the study population, the researchers had difficulty measuring secondary outcomes of neuropsychological performance.
The lower cannabis dose appears to offer the best risk-benefit ratio in this patient group, and future research on the topic should include studies that span weeks or months to evaluate the efficacy of cannabis on NeP over longer durations, the authors concluded.
1. Wilsey B, Marcotte TD, Deutsch R, Zhao H, Prasad H, Phan A. An exploratory human laboratory experiment evaluating vaporized cannabis in the treatment of neuropathic pain from spinal cord injury and disease. J Pain. 2016; pii: S1526-5900(16)30072-30074.
2. Cardenas DD, Jensen MP. Treatments for chronic pain in persons with spinal cord injury: A survey study. J Spinal Cord Med. 2006; 29:109-117.