Marijuana should not be sold to Canadians under the age of 21 because their brains are still maturing, Canada's doctors say.

The Canadian Medical Association is urging the federal government to take a slew of measures to keep legal pot out of the hands of teenagers and young twentysomethings, including restricting the amount and potency of the marijuana available to Canadians younger than 25.

The CMA, which speaks for 83,000 doctors across the country, made the recommendations in a written submission to the federal task force in charge of designing a new system for selling recreational pot in Canada. The nine-member panel is expected to report to the Liberal government – which has promised to legalize marijuana – in November.

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"If you were going just by the scientific evidence you'd probably land on something more like an age restriction at 25 because we know that most of the rapid brain development takes place right up until that age," said Dr. Jeff Blackmer, the CMA's vice-president of medical professionalism and policy development.

But the doctors group acknowledged that it would be difficult to set a minimum age of 25, considering pot use among Canadians 15 to 24 years old is already double that of the general population. It would be better to set a lower age limit and encourage younger marijuana users to steer clear of the black market, it argued.

"We recognize that people below the age of 25 will still likely want to try to use it and may then look to other avenues to obtain the drug, which may not be as safe," Dr. Blackmer added in an interview.

Jenna Valleriani, a PhD candidate at the University of Toronto and a strategic adviser for Canadian Students for Sensible Drug Policy, said it would make more sense to implement cannabis age restrictions that mirror those for alcohol – 18 or 19, depending on the province.

"If you have age limits as high as 25 you have the potential of creating this kind of youth illicit market," she said.

The CMA also weighed in on other aspects of a future marijuana regime that it hopes would be applied consistently from coast to coast.

The group recommended that pot be sold in places that already sell controlled substances – such as liquor stores – rather than in pharmacies, which could risk lending marijuana "credibility as pharmaceutical medication."

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"We've never felt comfortable with the idea of promoting [marijuana] as a medical product," Dr. Blackmer said.

Putting cannabis on the shelves of places like liquor stores, where the staff have experience asking for identification and warning customers of a product's risks, "sends a message that [marijuana] is a regulated product. This is not a health product. This is not going to make your health get better. In fact, there are health risks of consuming this product."

The doctors also urged Ottawa to ban homegrown weed, except for medicinal users; to enact strict laws against drugged driving; to forbid pot smoking in public places; and to undertake a "rigorous review" of the rules currently in place for producing, packing, storing and distributing medicinal pot before cannabis sales are opened up to recreational users.

Right now, medicinal marijuana can only be distributed legally by mail from cannabis producers approved by the federal government, but a grey market of storefront pot dispensaries has already emerged, especially in Vancouver and Toronto.

Earlier this year, a Globe and Mail investigation into the contents of marijuana from nine unregulated Toronto dispensaries found that three of nine samples of dried cannabis would not meet Health Canada's safety standards for licensed growers.