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A young man smokes a marijuana joint during a rally in downtown Vancouver, B.C., on Wednesday April 20, 2011. Members of Canada’s medical community are disappointed over a federal task force’s recommendation to allow cannabis sales to those 18 and over.

Darryl Dyck/THE CANADIAN PRESS

Members of Canada's medical community are disappointed over a federal task force's recommendation to allow cannabis sales to those 18 and over, with some warning unrestricted access could have a detrimental impact on developing brains.

As the government moves toward legalization, it also faces the enormous challenge of combatting the widely held mistaken belief that marijuana is harmless, according to a number of medical organizations and substance use experts.

The task force released its report Tuesday on what cannabis legalization and regulation may look in Canada, including a number of measures to restrict access to minors, such as a ban on advertisements and sponsorships and the use of plain packaging devoid of brand colours or logos.

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But one of the most contentious recommendations is around the legal age. The report suggests setting the purchase age at 18, but acknowledges that provinces may wish to harmonize it with the legal alcohol age, which is 19 in some parts of the country.

A 2013 Unicef report found that Canadian youth are the highest users of cannabis compared with other developed nations and the government said it hopes the move toward legalization can help bring those rates down.

The Canadian Medical Association had recommended a legal age of 21 because of evidence cannabis can cause changes to the brain and may pose a serious health risk to young people.

The task force said an older age limit could help fuel illicit sales of cannabis, particularly considering that young people between 18 and 24 tend to be some of the highest consumers of marijuana.

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But Jeff Blackmer, vice-president of medical professionalism at the Canadian Medical Association, said they took those concerns into account when recommending a legal purchase age of 21.

Since the brain develops until about age 25, the CMA saw its recommendation as a compromise that could help shield young people from the harmful effects, Dr. Blackmer said. "We based [our recommendation] on available medical and scientific literature and the concerns we had."

Dr. Blackmer added that the association will likely continue to talk to Parliament about the age restriction as the legalization process moves forward.

The Canadian Paediatric Society also expressed concern that no limits will be put in place to limit the concentration of tetrahydrocannabinol (THC) in cannabis products available to 18- to 25-year-olds. The society published a position statement last month calling for the limits because of mounting evidence of the effects of marijuana on the developing brain.

"I think it's fair to say we're disappointed," said Christina Grant, associate professor of pediatrics at McMaster University in Hamilton and lead author of the position statement.

Alistair Bursey, chair of the Canadian Pharmacists Association's board of directors, said it also advocated for 21 to be the legal age for purchase. But he acknowledged that setting it too high could fuel the illicit market.

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Regardless of the legal age, the consensus among medical experts is that the federal government must adopt a strong public education and awareness campaign to counter the myth that marijuana is safe.

The task force made several recommendations about public education and it's imperative for those measures to be taken seriously, Dr. Blackmer said.

"I don't think there's any Canadian ... who smokes cigarettes who thinks it's good for them," he said. "We've not done nearly as good a job educating people, particularly young people, about some of the potential dangers of marijuana use."

One of the clearest pieces of evidence that cannabis can cause lasting damage to the brain came in a 2012 New Zealand study that followed cannabis users over several decades.

Researchers found regular users had more cognitive problems than those who abstained, even after taking education levels into account. Those who began using cannabis during adolescence had the biggest cognitive declines. Research also shows that young people who use marijuana may be susceptible to psychosis, although there are questions about whether those risks are confined to people genetically predisposed to psychosis.

"The developing brain is a vulnerable brain," said Anthony Feinstein, professor of psychiatry at the University of Toronto who studies multiple sclerosis and how cannabis impacts cognition. "That's where there is a potential problem."

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