It may take up to five years before clinical trials could confirm many of marijuana's touted benefits, which is forcing doctors to grapple with a backward federal system in the meantime, says the president of the Canadian Medical Association.

Chris Simpson says physicians should not be prescribing medical marijuana in most cases because of the dearth of clinical research, despite efforts by commercial cannabis growers to fill the void.

"We're looking for the evidence to support a drug that's been made available, where usually it's the other way around," Dr. Simpson told The Globe and Mail. "We know that there's a history in medicine of lots of things that seem promising, but once they're subjected to the rigour of scientific inquiry, they turn out to be either not as good as advertised or harmful, rather than helpful."

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Dr. Simpson, however, does support the use of medical cannabis by terminally ill patients, those in palliative care, and said there is some evidence that a compound in the drug can help reduce seizures.

A year after the federal government overhauled the medical marijuana system, Health Canada has approved only one clinical pot trial, which involves patients with arthritic knees.

A University of British Columbia study of treating posttraumatic stress disorder could be approved as early as this September and another clinical trial led by an HIV/AIDS researcher at the same university could get approval and begin recruiting patients within a year, after announcing last week that he had received a million-dollar grant from another commercial cannabis grower.

In last week's Supreme Court of Canada decision ensuring marijuana patients' right to edible forms of the medicine, judges accepted that cannabis has anti-inflammatory and anti-spasmodic properties, increases the appetite of those taking other drugs, such as AIDS patients, and can help fight nausea for those undergoing chemotherapy.

Still, they agreed with a ruling from a lower-court judge that stated more medical research was needed on cannabis.

Without much clinical data, Dr. Simpson is concerned that most of the 19 licensed producers will continue their aggressive "educational outreach" campaigns targeting Canada's doctors, who, as gatekeepers, haven't received meaningful prescription guidelines from a federal government that doesn't endorse marijuana as a medicine. Barred from advertising their product to the public, he says these growers are "getting around" government rules by mass e-mailing doctors and putting on exhibits at health conferences.

"It's quite slanted," Dr. Simpson said of the information the pot growers provide. "We're not seeing TV ads, but they're aggressively marketing to physicians."

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Brent Zettl, CEO of Prairie Plant Systems Inc., the licensed grower behind the osteoarthritis study approved by Health Canada, is worried much of the research funded by his competitors isn't rigorous enough to sway the medical establishment. He said his company has spent more than a million dollars over the past three years preparing for the study and that funding such research "is not for the faint of heart."

"It's a right of passage: you've got a well-established system for medical trials in this country," Mr. Zettl said. "To circumvent that is to circumvent a system that's … proven and tried over a very significant period of time."

Mr. Zettl, whose company was the federal government's lone supplier of medical marijuana for 13 years leading up to the new system, said Canada's cannabis researchers could have led the world in their field if the federal government hadn't stopped almost all funding about a decade ago.

"If you talk to any researchers, they thought that was critical money that was set up for independent research," Mr. Zettl said.

About a decade ago, Health Canada cancelled funding for a study on marijuana and AIDS patients in Toronto. Later, the department stated that it believed clinical research was best funded by the pharmaceutical industry.

But drug companies have been loath to research marijuana because it offers no clear return on their investment.

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Arthur Caplan, a world-renowned medical ethicist, said it's disappointing that Ottawa isn't funding "a few studies" on the medicinal benefits of marijuana.

"It's a big enough issue that you'd expect the government funding to be there," said Mr. Caplan, head of medical ethics at New York University's school of medicine.

He added that due to the inherent conflict of interest, many in the medical community, rightly or wrongly, will likely be suspicious of pot research funded by commercial growers.

"There certainly is data that shows when a drug company sponsors a trial they tend to get more positive results," said Mr. Caplan.

He cautioned that no matter how much valid data exists, some doctors still won't accept that the stigmatized drug has any medical benefits.

"It's not clear that this fight is all about evidence, some of it is about the fear that medical marijuana may go to recreational [users] as it has in the States," Mr. Caplan said. "In the States, I think the argument was not going to swing on evidence, what happened was politics in favour of letting people use medical marijuana just overwhelmed the opposition."

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Pot study to look at drug's effects on osteoarthritis

Sponser: Prairie Plant Systems Inc., parent company of licensed marijuana producer CanniMed, based in Saskatoon.

Study: Randomized, double-blind, placebo-controlled clinical trial gauging effect of various strains of vaporized cannabis on adults with painful osteoarthritis of the knee. It will compare how seven strains of cannabis with different ratios of delta-9-tetrahydrocannabinol (known for its psychoactive properties) and cannabidiol (which is reportedly more therapeutic) affect each patient and their levels of pain.

Partners: McGill University, Dalhousie University and lab company Algorithme Pharma Inc.

When: Recruitment of 40 participants will begin next week and the company expects the study to be fully completed within a year.

Reason for study: Roughly 36 per cent of patients registered under the old federal medical marijuana system reported using the drug to treat their severe arthritis.

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Cost: The company will only say it has spent more than a million dollars in the three years preparing for the trial.