People who suffer chronic neuropathic or nerve pain from damage or dysfunction of the nervous system have few treatment options with varying degrees of effectiveness and side-effects.
Neuropathic pain is caused by damage to nerves that don’t repair, which can make the skin sensitive to a light touch.
Cannabis pills have been shown to help treat some types of pain but the effects and risks from smoked cannabis were unclear.
To find out more, Dr. Mark Ware, an assistant professor in family medicine and anesthesia at Montreal’s McGill University, and his colleagues conducted a randomized controlled trial — the gold standard of medical research — of inhaled cannabis in 21 adults with chronic neuropathic pain.
In what the researchers call the first outpatient clinical trial of smoked cannabis, investigators used three different strengths of the active drug — THC levels of 2.5 per cent, six per cent and 9.4 per cent, as well as a zero per cent placebo.
“We found that 25 mg herbal cannabis with 9.4 per cent THC, administered as a single smoked inhalation three times daily for five days, significantly reduces average pain intensity compared with a zero per cent THC cannabis placebo in adult subjects with chronic post traumatic/post surgical neuropathic pain,” the study’s authors concluded in Monday’s online issue of the Canadian Medical Association Journal.
The researchers also found improvements in measures of sleep quality.
The most common drug-related side-effects during the trial among those receiving the highest dose were headache, dry eyes, burning sensation in areas of neuropathic pain, dizziness, numbness and cough.
“Because the study was short duration, the exposure was quite small and the patients only used each strain for five days, the question is what about longer term exposure?” Ware said. “Would they get better pain relief or would it plateau or would it fall off if they used it for longer?”
Those questions, as well as safety concerns, still need to be studied, the researchers said.
“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,” Dr. Henry McQuay of Balliol College, Oxford University, U.K., said in a journal commentary accompanying the study.
McQuay concluded that the trial adds to the “trickle of evidence that cannabis may help some of the patients who are struggling at present.”
The commentary called for more research into whether specific pain mechanisms respond to cannabis.
The marijuana for the study was obtained from Prairie Plant Systems of Saskatoon and the U.S. National Institute of Drug Abuse.
The Canadian Institutes of Health Research and the Louise and Alan Edwards Foundation funded the study.
McQuay declared being a member of advisory boards and consultant to several pharmaceutical companies. He also provided expert testimony and received lecture payments from drug makers and received royalties for a textbook on pain.