Countries in the world where marijuana is legal for recreational use to some extent, and not just decriminalised, include Colombia, Ecuador, Peru, Spain, Uruguay, India, the USA, and the Netherlands.

The rules are different from place to place and there are lots of grey areas. For example, in Uruguay cannabis is totally legal and you can smoke it in the street, but in Spain it's only legal in private spaces.

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In some other countries, cannabis possession is illegal, but either decriminalised – so those caught with small amounts have it confiscated and are given a fine, for example – or tolerated by authorities who turn a blind eye.

In the US, cannabis is illegal at the federal level, but certain states allow for its medical and personal use. American states which allow for recreational cannabis use are Alaska, California, Colorado, Maine, Massachusetts, Nevada, Oregon, and Washington. It is also legal in Washington, DC.

Canada will become the latest country to legalise marijuana for recreational use if the government's plans pass into law. The Canadian broadcaster CBC said Prime Minister Justin Trudeau would unveil legislation to legalise and regulate cannabis in April. It should then be legal in Canada by 1 July, 2018.

There appears to be a shift away from drug criminalisation in public policy. Attitudes are changing. Softer drugs are seen by many as no more harmful than alcohol, and in some cases, such as cannabis, can have medicinal benefits.

And it's argued by proponents of decriminalisation that harm prevention is a more effective way of tackling hard drugs, such as heroin, because it removes control of the industry from organised criminals and the black market.

Several states in the US have only recently made cannabis legal for personal use. It has for some years been medically legal in many areas of America, but in 2012 Colorado and Washington become the first states to make the recreational use of marijuana properly legal, not just decriminalised.

In Colorado alone, the cannabis industry – both medical and recreational – is now worth $1bn (£795m), generating $135m in taxes and license fees for the public purse.