Why is Canada legalizing marijuana, and why does the move – if done right – make sense? It's all about harm reduction.

Smoking marijuana has real health risks, particularly for young people. But the long-standing ban on the sale of pot isn't addressing them. The drug is widely available and widely used; according to the OECD, Canada has the developed world's highest rate of youth pot use. Prohibition's only real accomplishment is as an unintended industrial strategy, fostering a multibillion-dollar black market.

The federal government is ending the criminal ban on pot, but almost everything that happens after that is up to the provinces. Each has to strike a difficult balance: making pot available legally and widely, thereby pushing out the black market, while simultaneously creating a framework for discouraging the use and abuse of the drug, especially among teenagers and young adults.

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From coast to coast, each province is likely to handle legalization differently, and that's a good thing. One of federalism's benefits is it lets the country run parallel experiments, so voters and governments can discover what works best. The province that wins this game is the one that shifts the most pot sales from the street to the legal market – while simultaneously leading the country in lowering marijuana use among young people.

It won't be easy, but it is possible. Two products with which governments have a lot of experience point the way: Alcohol and tobacco are the models for harm reduction.

Decades ago, alcohol prohibition was dropped in favour of legal sales. That happened because, despite the dangers of drink, outlawing booze gave rise to new and larger harms. Prohibition was a utopian approach: It aimed at harm-eradication, but delivered harm-multiplication. It has been replaced by a more realistic attempt at reducing harm through legalization, regulation and education.

With the end of prohibition, organized crime left the booze business. And while alcohol abuse remains a major health problem, its dangers have been gradually reduced. For example, the rate of drunk driving in Canada has fallen by more than two-thirds since 1989.

It's a similar story with cigarettes. Tobacco is addictive and smoking is terrible for human health, yet adults can buy cigarettes at any corner store. To discourage smoking, Canada uses a combination of taxation, regulation, stigmatization and education. In 1965, fully 50 per cent of Canadians were smokers, according to Physicians for a Smoke-Free Canada. By 2011, despite the widespread availability of cigarettes, the rate had fallen to just 17 per cent. In stark contrast to pot use, Canada has the developed world's lowest rate of youth smoking, according to the OECD.

The harms from tobacco and alcohol have not been eliminated, because that's not a realistic goal. But they have been reduced, while further reductions are always being sought.

Reasonable people can debate whether recreational marijuana is as bad as drinking and smoking. But it's pretty clear that it has downsides for human health, particularly when the humans in question are children or young adults. Research shows that those most at risk from marijuana use are under the age of 25, because their brains are still developing.

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Yet according to Statistics Canada, teens and young adults are more likely than those over 25 to have used marijuana in the past year.

Canada's experience with alcohol and tobacco suggest that, if done right, marijuana legalization has a shot at improving the situation – cutting organized crime out of the equation, leading to a more law-abiding society, and, through regulation and education rather than prohibition, less use and less abuse.

Last week, Ontario announced its blueprint for doing just that. It's better than prohibition, but it's also flawed, and not what other provinces should copy.

Once the federal government fully legalizes recreational marijuana on July 1, 2018, the legal age to purchase it in Ontario will be 19 – the same as alcohol.

The scores of pot "dispensaries" that have recently sprouted up will still be illegal. Ditto for "that guy" who sells in your neighbourhood. The only legal seller of recreational marijuana in the province will be the government-owned Liquor Control Board of Ontario. The government says the price of pot will be low enough to compete with the black market, thereby snuffing out illegal sales.

The big flaw in Ontario's plan is this: The LCBO, one of the world's largest buyers and sellers of alcohol, won't be allowed to take full advantage of its enormous reach. Marijuana won't be sold in any of its existing 660 stores. Instead, the LCBO is going to set up a separate, and much smaller, retail marijuana operation.

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It will offer online sales and home delivery, but when legalization arrives next summer, the LCBO's new pot arm will have just 40 stores open, rising to 150 by 2020. That's a much smaller footprint than the province's various illegal retailers. And that's a problem.

Legalization aims at getting rid of the black market, and replacing it with clean and legal sources of supply. But by so limiting the number of legal places to buy pot, Ontario risks helping the illegal market remain very much in demand. Allowing LCBO liquor stores to sell pot, or licensing and regulating even larger numbers of private retailers, as is done with beer and alcohol in some provinces, and with thousands of private stores selling tobacco, is a better approach.

Ontario is also restricting where marijuana can be smoked, with limits more stringent than those on tobacco smoking. The new right to use marijuana can't involve imposing second-hand smoke or other dangers on your fellow citizens – hence a ban on pot use in a car, similar to the long-standing ban on open alcohol.

Most other provinces have yet to release their legalization plans. They should carefully study what Ontario is doing, and improve on it.