As a pediatrician, Dr. Larry Wolk was trained to treat marijuana as "bad" and "illegal" — and to counsel patients against using it. 

And that his history shaped the way he approached the introduction of legal marijuana as Colorado's chief medical officer, he said.

"I think I came into this with some biases as a result of our culture, prior to legalization," he told CBC News.

But nearly three years after legalization in Colorado, he said his thinking changed at each turn.

On almost every measure, whether it was rates of hospitalizations, consumption among teens and adults, or collisions related to marijuana, the pattern was the same: an initial increase, and then long term stabilization with no increase from the rates prior to legalization in January 2014.

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A customer pays cash for marijuana at the Dank dispensary in Denver, Colorado. (Solomon Israel/CBC)

"And so to say I wasn't surprised would not be honest," Wolk said. "I have to say I was surprised but I also learned a lot about making sure in these kind of roles, like I'm in, that you park those biases and you stay objective."

Wolk was in Ottawa earlier this month to meet with Health Canada officials from across the country — and share lessons learned from the Colorado experience as Canada gets set take its own journey down the path of marijuana legalization next year.

Here are some of those lessons:

Minimum age

Colorado: 21, same as the legal drinking age.

One of the most hotly contested issues among health agencies across Canada is about setting the right minimum age for legal marijuana.

On Monday, Ottawa Public Health will table before the local health board its recommendations to the federal task force examining what a legal pot regime should look like.

"We wanted to ensure that we're reducing access for youth," said Gillian Connelly, manager of Health Promotion and Disease Prevention with OPH.

"One of the things that the research clearly demonstrates is that early access to cannabis can have detrimental effects for brain development — and the brain develops up to age 25."

But Wolk said he doesn't disagree with the clinical reasoning

"I think you have to weigh that against some of the practical consideration, which is that there are a fair number of young adults who are using marijuana illicitly here in Colorado and in Canada, in certain parts of the country, at a fairly high rate of prevalence," he said. 

"And so do you capture that and address that by legalizing it so now you can do the appropriate amount of surveillance and education and ongoing research — or do you continue to try to sort of fight the fight and say that its illicit up until 25?"

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Age of onset for marijuana use may make a difference in how the brain is affected, researchers say. (Richard M. Hackett/Longmont Daily Times-Call/Associated Press)

Impact on teens 

Colorado: no increase in rate among teens.

Bracing for an impact on teenage marijuana smoking rates, Wolk said Colorado used an aggressive program targeting teens with education, surveillance and research. The program was funded by state income from the sale of marijuana.

"Teen usage has not gone up," Wolk said, adding that it's too soon to know whether programming targeting to teens is working.

"While the rates haven't gone up, they haven't gone down either," he said. 

Impact on adults

Colorado: no long term impact.

Wolk said health officials were ready for an increase in usage among adults — but that didn't happen.

"We started with a relatively high use rate amongst adults prior to legalization (compared to the national average) and so, by and large, it's adults using illicitly prior who are using legally now, but we haven't really seen an increase in regular users since (legalization)."

Emergency visits, collisions, injuries

Colorado: short term increase, but a return to pre-2014 levels in the long term.

"What we're hearing and what we're seeing across the board is that those hospitalizations and those emergency room visits have since leveled off," Wolk said, adding "the only increase trend is coming from folks from outside Colorado who come to Colorado."

He said people who "are inexperienced" or have not been educated about marijuana might not be "familiar enough with products to keep themselves out of trouble."

He added that the increase in visitors to Colorado has been lacklustre, with a very modest two to three per cent increase in tourism.

Edible marijuana products

Colorado: introduced new legislation about marketing edibles in October.

Dan Anglin

Americanna president Dan Anglin displays packages of cannabis-infused gummy candies at his company's facility in Boulder, Colorado. (Solomon Israel/CBC)

OPH recommended to a federal task force that they learn from the Colorado experience, particularly on a gap in regulations surrounding edible marijuana products.

Wolk said the state hadn't considered the impact of "creative marketing" around edible products on children and teens, but legislators have since introduced packaging laws similar to how Canada deals with cigarettes.

"I think, in an effort to be creative and innovative in their marketing to adults, they arguably inadvertently made many of these edibles enticing to children. You know, candy bars, brownies, gummies," Wolk said, adding that young children could eat an "enticing"  marijuana product" without knowing it.

Canadian advantage

Wolk said that Canada has an advantage over Colorado's experience, because it's drafting national legislation. 

"Many of the challenges related to legalization, from a public safety standpoint, really have to do with the fact that it's legal in Colorado but it's illegal in all of our surrounding states," Wolk said, adding that Oklahoma and Nebraska have both tried — and failed — to sue Colorado over its drug laws. 

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OTTAWA, ON - JUNE 5: A Canadian flag with a marijuana leaf flies during a rally in support of legalizing marijuana. (Donald Weber/Getty Images)

"We know that there's a grey market, if not a black market, for trying to grow legally in Colorado and transport across state lines where it has street value. So I would think that by having a national approach to legalization, it really does help minimize the potential black market impact, and the criminal market and valuation of the street marijuana because you've taken all of that away."