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International Centre for Science in Drug Policy has released a list of 11 common claims about the use and regulation of pot that research shows are actually incorrect.Ben Nelms/The Globe and Mail

Conservative Canadian politicians continue to feed myths such as the legalization of marijuana in Colorado has led to a spike in teen use and that a clear link has been established between cannabis use and mental illness, says an international network of drug policy scientists and academics.

The Toronto-based International Centre for Science in Drug Policy attempted to inject itself into the federal election campaign on Wednesday by releasing a list of 11 common claims about the use and regulation of pot that research shows are actually incorrect. Such false claims about marijuana lead to policies that actually put youth at risk, the researchers say.

Conservative Leader Stephen Harper has made Canada's approach to marijuana laws an election issue, contrasting his government's tough approach to pot against the Greens' and Liberals' plan to fully legalize the drug and the NDP's pledge to at least decriminalize it and study legalization. At a campaign stop earlier this week, Mr. Harper unveiled his party's three-pronged plan to strengthen its national drug strategy and attacked Liberal Leader Justin Trudeau's position.

"The statistics in places like Colorado are very clear on this, that, when you go down that route [toward legalization], marijuana becomes more readily available to children, more people become addicted to it and the health outcomes become worse," he told a rally Tuesday in Markham, north of Toronto.

However, M. J. Milloy, an infectious-disease epidemiologist with the B.C. Centre for Excellence in HIV/AIDS, said his group's research proves that recent use by teens in Colorado has gone down from 22 per cent to 20 per cent in the first year that the U.S. state regulated recreational pot sales. The Conservative Party did not respond to calls for comment on the report.

"It's not a sort of a 'push a button, get the result' type thing," Dr. Milloy said. "We've had, what, 40 years of doing things Mr. Harper's way, both under his government and under previous governments, which have enacted a very stringent cannabis prohibition model.

"Where are we after billions of dollars and thousands of arrests? We are at a place where Canadian teens lead the world in marijuana use."

Last summer, NDP Leader Thomas Mulcair told media that the pot he smoked as a student decades ago is "about as strong as oregano" compared with what's available today. The new report called the claim that marijuana's psychoactive THC compound is now more than 300 per cent stronger exaggerated, though studies suggest there have been increases in its potency in some jurisdictions over time.

Mr. Mulcair has denied the suggestion that pot is a "gateway" to other, harder drugs, and the new report echoed his assertion, finding no evidence of that phenomenon.

The ICSDP researchers also found the evidence that marijuana is a highly addictive drug is weak, noting less than 10 per cent of people who use cannabis throughout their life will become dependent. In contrast, it's estimated that about a fifth of those who use heroin, cocaine or alcohol across their lifetime are at risk of becoming addicted, the report added. People who smoke throughout their lives run a 67.5-per-cent estimated risk of becoming addicted to nicotine, the report noted.

As part of Mr. Harper's anti-drug strategy announced earlier this week, the Conservatives committed to prioritize government-funded research on the link between substance abuse and mental health. Dr. Milloy said the scientific evidence doesn't back up such a shift, noting that rates of schizophrenia haven't increased in parallel to the global rise in marijuana consumption in recent decades.

In recent years, national surveys have shown a majority of Canadians want to loosen marijuana laws, with an Angus Reid Global poll reporting last year that 60 per cent of respondents supported legalization.

Dr. Milloy, who recently received a million-dollar grant to study how pot may help fight HIV/AIDS, said the "unscientific claims" make it more difficult for researchers to do work that could save people's lives.

Researchers say pot prohibitionists are spreading harmful myths, and they single out Stephen Harper and his Conservative government as repeat offenders

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