For patients with chronic (long-term) neuropathic pain, smoking cannabis was found to reduce symptoms of pain, improve mood and help sleep, a report published in CMAJ (Canadian Medical Journal Association) revealed. When damage or dysfunction of the nervous system results in chronic neuropathic pain, patients have few treatment options, such as antidepressants, local anesthetics, anticonvulsants or opioids. However, these medications often have undesirable side effects and do not work for everybody.

However, researchers from the Mayo Clinic said medical marijuana is not recommended for teens with chronic pain.

The authors in the article published in CMAJ inform that oral cannabinoids have been effective in reducing the symptoms of some types of pain. However, they many have different effects and risks compared to smoked cannabis.

Investigators from McGill University Health Centre (MUHC) and McGill University carried out a randomized, controlled trial to determine the analgesic effect of smoked cannabis in 21 patients, aged 18 years or more, all of them with chronic neuropathic pain. THC levels (drug potencies) were divided into 2.5%, 6% and 9.4%. Some participants also received a placebo (0%).

The researchers inform that there was a correlation between increased THC content and better sleep quality. Symptoms of depression and/or anxiety were also reduced at 9.5% THC level.

Lead author Dr. Mark Ware, Director of Clinical Research at the Alan Edwards Pain Management Unit of the MUHC, said:

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. We found statistically significant improvements in measures of sleep quality and anxiety.

The authors believe their study is the "first outpatient clinical trial of smoked cannabis ever reported." As there have not been many studies on smoked cannabis for neuropathic pain, the investigators say there should be further, longer-lasting trials with higher THC potencies. Long-term safety studies of smoked cannabis for medical purposes are also needed, they added.

Dr. Henry McQuay of Balliol College, Oxford University, UK, writes in a related Commentary:

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.

"Smoked cannabis for chronic neuropathic pain: a randomized controlled trial"
Mark A. Ware, Tongtong Wang, Stan Shapiro, Ann Robinson, Thierry Ducruet, Thao Huynh, Ann Gamsa, Gary J. Bennett, Jean-Paul Collet
Published online ahead of print August 30, 2010
CMAJ 10.1503/cmaj.091414

Commentary: "More evidence cannabis can help in neuropathic pain"
Henry J. McQuay
Published online ahead of print August 30, 2010
CMAJ 10.1503/cmaj.100799

Written by Christian Nordqvist