Saturday, September 4, 2010

Is Smoking “Pot” Helpful for Neuropathic Pain?

Medical MarijuanaA recently-published report in the Canadian Medical Association Journal suggests that smoking marijuana, or “pot,” can reduce symptoms of pain, improve mood, and aid sleep in patients with chronic neuropathic pain. However, this study actually provides only a smidgen of valid evidence and much more research is needed before patients are advised to “light up” for better pain relief.

Investigators from McGill University in Montreal, Quebec, conducted a randomized, controlled, cross-over trial to determine the analgesic effect of smoked marijuana (cannabis) in 21 patients — mean age 45 years, 12 women — all of whom were experiencing chronic post-traumatic or postsurgical neuropathic pain [Ware et al. 2010]. During each cycle, participants inhaled a single 25 mg dose of cannabis 3 times daily for 5 days, followed by a 9-day washout period. The cannabis THC level (marijuana drug potency) for each randomly assigned cycle was either 9.4%, 6%, 2.5%, or 0% (placebo).

Average daily pain intensity (on an 11-point visual analog scale) was significantly reduced by 9.4%-THC cannabis compared with placebo (p=0.023), whereas other levels of THC yielded little added pain relief. Compared with placebo, participants receiving the highest level of THC also reported greater ease in falling asleep, improved sleep quality, and reduced anxiety; however, no other significant differences in mood or quality of life were found at any level of THC. There were assorted reports by participants of psychoactive effects — eg, dysphoria, lack of concentration — but these did not result in any trial dropouts; euphoria or “high” was reported on only 3 occasions throughout the study. Common drug-related adverse events included headache, dry eyes, dizziness, numbness, and cough, some of which may have related to smoke inhalation, whether active drug or placebo (35% of participants had never smoked before).

CONCLUSIONS/COMMENTARY: The researchers concluded that inhaling 25 mg of smoked marijuana with 9.4% TCH content several times a day for 5 days significantly reduced pain intensity in adults with chronic neuropathic pain. However, while the pain reduction was statistically significant, the absolute mean difference in pain scores compared with placebo was modest (difference 0.7, 95% CI 0.02-1.4) and may not be clinically significant. There also were some inconsistencies in data reporting in the published article that add some confusion, and the small number of participants did not lend much statistical power for valid analyses.

Still, this is an important topic because patients with chronic neuropathic pain have relatively few treatment options, such as antidepressants, local anesthetics, anticonvulsants, or opioids, as noted in a recently-reported research review [see our blogpost on this]. It was noted in that review that cannabinoid agents (oral, not smoked) have demonstrated limited effectiveness for neuropathic pain. While many patients with pain smoke marijuana for medicinal purposes and anecdotally report its benefits, there has been very little research aside from laboratory experiments involving small numbers of human volunteers. This present, Canadian, study may be the first to enroll outpatients in this type of research; however, it contributes only a modicum of evidence that cannabis is of clinically significant benefit for neuropathic pain. Much larger, longer-term trials of high-THC-potency marijuana, smoked more frequently, and assessing both efficacy and safety may be warranted, if the adversarial political climate surrounding this drug will permit it.

REFERENCE: Ware MA, Wang T, Shapiro S, et al. Smoked cannabis for chronic neuropathic pain: a randomized controlled trial. CMAJ. 2010(Aug 30); online ahead of print [abstract here]. Full-article PDF was available [here] at the time this blogpost was published.