Marijuana flowers and leaves were blended into three different strengths for the study. (Eric Risberg/Associated Press)

Smoking marijuana does help relieve a certain amount of pain, a small but well-designed Canadian study has found.

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.

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.

Short study

Study participants inhaled the 25-milligram dose through a pipe for five days and then took no marijuana for nine days. Then they rotated through the other doses of THC.

The participants also reported improvements in measures of sleep quality, the researchers said.

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.
• 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?"

'Trickle of evidence'

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.

It is important for doctors to screen patients carefully for substance abuse problems before prescribing marijuana for pain relief, said Dr. Sandy Buchman, a family doctor in Toronto. His practice now consists mainly of seeing cancer patients at their homes near the end of their lives.

Buchman has prescribed marijuana to dozens of patients. Until now, however, it has been difficult to measure the dose in forms other than pills, he said.

"Having this kind of guidance and then further studies to delineate the dose and response would be extremely helpful," said Buchman.

'I swear by it'

Amy Brown of Toronto did not participate in the study, but uses marijuana for the chronic pain and swelling in her wrist. She broke several bones, including in her wrist, five years ago in a car collision.

"I was very skeptical, but I tried it and it worked," said Brown, who has a grower's licence from Health Canada. "Now I swear by it. I won't go back to any kind of pills for my pain."

Brown described her pain as a sharp, burning, throbbing pain that just comes "out of nowhere." Brown said she also feels pain when she uses her swollen wrist, such as for turning a door knob on a wet day.

The marijuana for the study was obtained from Prairie Plant Systems of Saskatoon and the U.S. National Institute on Drug Abuse.

The federal government awarded a contract 10 years ago to Prairie Plant Systems to provide a standard supply of medical marijuana. The company now offers a product that is 12 per cent THC, Ware noted.

The Canadian Institutes of Health Research and the Louise and Alan Edwards Foundation funded the study.

With files from The Canadian Press