If Canada's new government chooses to legalize marijuana beyond medical use then it should get into the business of controlling its supply and sale to prevent the rise of a "Big Cannabis," addiction specialists say.

Cannabis policy could be an issue ahead of October's federal election. The governing Conservative party favours the status quo, the competing Liberals seek to legalize, regulate and tax, and the New Democrats support decriminalization. The Green Party has said it would legalize and tax marijuana.

Where Canadian political parties stand on marijuana, CBC's fifth estate

In a commentary published in Monday's issue of the Canadian Medical Association Journal, addiction doctors describe the negative aspects of prohibiting cannabis use, such as fuelling the illegal drug trade and the high costs and harms associated with policing and prosecuting people.

Often the harms from prohibition versus harms from potential increased use of cannabis are falsely pitted against each other, doctors say. (Siavash Dezvareh/CBC)

"We're hoping to provide some direction to policy-makers in Canada to encourage them to rethink their current policies around cannabis, to move away from prohibition because it doesn't work and has a lot of harms associated with it," Dr. Sheryl Spithoff, a family physician and addiction doctor at Women's College Hospital in Toronto and one of the coauthors of the paper, said in an interview.

Often the harms from prohibition versus harms from potential increased use of cannabis are falsely pitted against each other, Spithoff and her team said. But cannabis prohibition has shown to have no effect on rates of use in developed countries.

"A frequently cited concern with legalization is that it will allow the rise of Big Cannabis, similar to Big Tobacco and Big Alcohol. These powerful multinational corporations have revenues and market expansion as their primary goals, with little consideration of the impact on public health. They increase tobacco and alcohol use by lobbying for favourable regulations and funding huge marketing campaigns. It is important that the regulations actively work against the establishment of Big Cannabis," the authors wrote.

They suggest that policy-makers draw on the extensive research on tobacco, alcohol and cannabis policy frameworks developed by public health researchers to create a Canadian approach that maximizes benefits and minimizes harm of the potentially addictive substance.

A 2013 UNICEF report found that the prevalence of self-reported cannabis use among youth aged 11, 13 and 15 in the preceding year was highest in Canada at 28 per cent. Findings in other countries included:

Norway — 4%.

Spain — 24%.

The Netherlands — 17%.

United Kingdom — 18%.

U.S. — 22%.

"Our hope with legalizing it is that less youth will have access to it," Spithoff said. "We'll be able to achieve our public health objectives, restricting access; limited hours that stores are open; and also young people won't have to go the illegal market to access cannabis. Especially for young adults, that's risky. It allows them to be exposed to other substances, more harmful substances."

In 2014, the Toronto-based Centre for Addiction and Mental Health estimated enforcement of cannabis laws costs Canadians $1.2 billion a year.

Spithoff said the harms of prohibition to individuals include the criminal records of 500,000 Canadians because of cannabis possession, stigma around its use and barriers to medical marijuana treatment.

In the CMAJ paper, the authors also compare the experiences with marijuana policies in the Netherlands, Spain, Uruguay and three U.S. states, where cannabis is legal for recreational use.

For example, Spithoff said Uruguay has a model that could be adapted for use in Canada, because it puts public health first. In contrast, the Dutch model hasn't solved the "back door" illegal supply problem.

Uruguay has licensed producers and a government commission that purchases cannabis from growers. The government sells it to individuals through pharmacies. The commission has control over production, quality and prices and has the ability to undercut the illegal market. Uruguay has also set a cutoff for cannabis-impaired driving.

Canada legalized marijuana for medical use in 2001. Detailed rules for commercial production and use of medical marijuana were implemented in 2014.

At a marijuana dispensary in Toronto, the idea of legalizing recreational pot was met with skepticism.

While cannabis advocate Amy Brown welcomes some regulation, she disagrees that pot is a public health concern any more than tobacco or alcohol. She worries about what government control would mean for growing the plant.

"The word 'monopoly' is where I disagree. A monopoly means complete and utter control of this product," Brown said. "Maybe an advisory board would be beneficial so that moms and pops who are growing their own cannabis can still grow their own."