People who suffer from chronic neuropathic pain due to damage or dysfunction of the nervous system have few treatment options. These options include opioids, anticonvulsants, antidepressants and local anesthetics, but efficacy varies and all have side effects which limit compliance. Oral cannabinoids have shown success in treating some types of pain but may differ in effect and risks from smoked cannabis.
A team of researchers from McGill University Health Center (MUHC) and McGill University conducted a randomized controlled trial to investigate the analgesic effect of inhaled cannabis in 21 participants 18 years and older with chronic neuropathic pain. The researchers used three different potencies of active drug (THC levels of 2.5%, 6% and 9.4%) as well as a 0% placebo.
Patients reported better sleep quality as the THC content increased. Anxiety and depression also decreased in the 9.4% THC group compared with the placebo group.
"We found that 25 mg herbal cannabis with 9.4% THC, administered as a single smoked inhalation three times daily for five days, significantly reduces average pain intensity compared with a 0% THC cannabis placebo in adult subjects with chronic post traumatic/post surgical neuropathic pain," reports lead author Dr. Mark Ware, Director of Clinical Research at the Alan Edwards Pain Management Unit of the MUHC. "We found statistically significant improvements in measures of sleep quality and anxiety."
"To our knowledge, this is the first outpatient clinical trial of smoked cannabis ever reported," the authors state. It is one of only a handful of studies on smoked cannabis and neuropathic pain. The authors recommend more studies with higher potencies of THC, longer duration of follow-up and flexible dosing. Long-term safety studies of smoked cannabis for medical purposes are also needed.
In a related commentary www.cmaj.ca/embargo/cmaj100799.pdf, Dr. Henry McQuay of Balliol College, Oxford University, UK, writes "the authors should be congratulated for tackling such a worthwhile question as: does cannabis relieve neuropathic pain, particularly because the trial must have been a major nightmare to get through the various regulatory hurdles. What makes it a worthwhile question is the continuing publicity that patients see, hear and read, suggesting analgesic activity of cannabis in neuropathic pain, and the paucity of robust evidence." He concludes that "this trial adds to the trickle of evidence that cannabis may help some of the patients who are struggling at present."