A study evaluating the effect of medical marijuana on arthritis is recruiting patients in Halifax and Montreal.

The Dalhousie University study will be the first to measure the effect of vaporized cannabis with different amounts of cannabinoids.

Dr. Mary Lynch is leading the study.

"It's helping us to move forward in identifying what are the best products that are going to be the most help, causing the fewest side effects," she says.

Patients aged 50 or older with osteoarthritis knee pain in Halifax and Montreal will be given several doses of vaporized medical marijuana with varying amounts of THC and CBD.

CBD is a non-psychoactive agent found in cannabis, while THC is a psychoactive agent. Researchers hope CBD will be able to fight pain without the side effect of getting high.

The study will be double-blind, with a control placebo. Neither participants nor researchers will know which participants are taking the real plant and which placebos.

Researchers will then monitor how participants react to the marijuana and measure their pain. Lynch says it's much needed research.

"The treatments that we have right now are inadequate to control all pain," she says. "They're all associated with side effects, different drugs work better in different people depending on their genetics, and we are desperate for new treatments."

Dr. Mary Lynch says more research is needed into the effect of marijuana on pain. (CBC)

A total of 40 patients are being recruited for the study. Already, Lynch says there is overwhelming interest.

"The phone's ringing off the hook and we've received lots of e-mails from people who have osteoarthritis, who are over 50, and interested in the study," she says.

Adam Richardson, with the Maritime Region of the Arthritis Society, calls the study a step forward for Nova Scotians with arthritic pain.

"It's something that we want to see governments look into," he says. "This is obviously research being done on a large scale, it's peer-reviewed, it's national."

The study is being paid for by the medical marijuana producer CanniMed.

Results should be in ready in about 18 months.