O Cannabis, as the title of Canada’s graceful national anthem doesn’t quite go. As the first major western economy to legalise cannabis the Canadian experiment – bold as it is – will serve to blow away some of the clouds from what has often been an overly emotional debate about the recreational use of the drug in this country.

It is certainly an important moment. Canada, as with the rest of the world, has since the 1920s attempted to enforce a policy of prohibition urged on the rest of the world by its powerful southern neighbour. The first of many waves of paranoia (ironically) about “reefer madness” resulted in the first declaration of the global war on drugs that is still being fought, with dispiriting lack of success, today.

When Canada completes the legalisation of cannabis not even one of Donald Trump’s famous walls will be able to stop it gliding south to the US. It will add friction to the already strained relations between Washington and Ottawa, though American cannabis users may cherish the supply of a quality-controlled, reliable product, free of links with crime, people smuggling, money laundering and the rest.

Now, with similar moves towards liberalisation in some US states, Uruguay, Portugal and the Netherlands, there is a sense that momentum is moving away from treating cannabis as law enforcement issue, and towards its control and regulation for adult use in a sensible way.

The debate has been pushing one way and then another for decades. In Britain cannabis has seen its classification move down from one of the most dangerous of drugs, on par with heroin, say, and then back up again. Medical reports suggest different things about its social effects. Police advice, and practice, also varies a good deal. What happens in Canada in the coming years will help the world to understand what the alternative to the current situation is. For those who feel police resources and the criminal justice system have better uses it will be important for them to be able to make their case. Even as things stand, most busy police officers feel no great need to prioritise nabbing someone with a little lump of resin in their pocket.

Cannabis itself is also changing, which is why the medical research into its effects and the practical experience of legalisation is so crucial. Much of the retail supply of the drug is with higher concentrations of the active ingredient THC than was available to, say, the hippies of the 1960s. There suggestions that the emergence of skunk and similar higher potency variants can add to the risk of exacerbating existing mental health conditions for example.

Then again, the emergence of synthetic cannabinoids such as the notorious “spice” has left much of the debate about legalising cannabis itself behind. How Canada deals with the dizzying variety of synthetic drugs that ape the effects of cannabis will be fascinating to watch, and to learn from. Inevitably some varieties of synthetic cannabinoids or of super-strength skunk may need to stay banned; how that is done when cannabis is generally more freely available is another challenge for Canada’s new breed of dope police.

Legalisation need not be synonymous with a free-for-all. Alcohol, tobacco and many potentially harmful foodstuffs are legal but highly regulated. Their sale is licensed and the product clearly labelled and tested for purity and strength. Users will have much clearer idea of what they are consuming than they do now: but, like a bottle of Scotch, that does not mean that overindulging isn’t dangerous to physical and mental health.

Despite the energetic argument and passion it arouses among users and opponents alike – in contrast to its immediate effects of relaxing minds and muscles – the cannabis question is, at base, a practical, empirical matter. Cannabis is not, generally, good for its users, apart from those with clear medicinal need for it, such as those with MS. As with other troublesome substances it needs to be controlled, but with some skill and judgment. Waging war on it plainly drives the trade underground, links it to crime and makes the product adulterated and unreliable is use. Complete liberalisation would make the damage it can bring more widespread and severe. Canada will now have the opportunity to lead the world in getting its approach right.