The war on pot has failed – so should we legalise cannabis?

What has happened?

The chief medical officer for England, Professor Sally Davies, published a report this month finding "conclusive evidence" of the effectiveness of "cannabis based medicinal products" for treating ailments such as chronic pain, chemotherapy-induced vomiting and multiple sclerosis.

The review followed extensive media coverage of the case of 12-year-old Billy Caldwell, who relies on cannabis oil to control epileptic seizures. The oil was confiscated from his mother by UK customs officials in June and could only be used following special intervention from the home secretary.

The case has sparked renewed debate about rules governing the medical and recreational use of cannabis, with former Tory leader William Hague and the chief of Durham police among those now calling for an end to prohibition of the class B substance. The British debate comes at a time when the legal backdrop for the "devil's lettuce" is changing fast on the other side of the Atlantic.

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Where is cannabis legal?

Uruguay decriminalised some drug possession as long ago as 1974 and fully legalised cannabis in 2013. Portugal, meanwhile, decriminalised all drugs not just cannabis in 2001. Decriminalisation means that users will no longer incur a criminal record for their habit, although there is still a ban on sales. Legalisation implies that the supply side is also within the law: cultivation, transport and retailing are allowed.

In the US, 31 states now allow marijuana to be used for medical purposes, with Germany, Italy and Spain among several European states authorising it for medical use. Despite being illegal under US federal law, cannabis is legal for recreational use in nine states and decriminalised in another 13. California is the latest state to bring it within the law, while Canada will become the first G7 nation to do so in October.

Why the shift?

Campaigners for legalisation have long pointed out that outlawing the drug has failed. It is widely available and teenagers say they can get hold of it more easily than cigarettes and booze. "Issuing orders to the police to defeat [the use of cannabis] is about as up-to-date and relevant as asking the army to recover the Empire," as Hague puts it. If the war on cannabis is impossible to win, we should stop wasting money on it. The cash saved on prosecutions would be supplemented by taxing the drug as we do alcohol and cigarettes (which many consider more harmful than pot).

Finally, the potency of the drug has increased sharply in recent years, with skunk, a strong form of cannabis that has been linked to psychosis, becoming more prevalent. Such strains now make up some 94% of police seizures of cannabis. If the drug were regulated by the state, the versions on sale could be made weaker and people would be more willing to come forward and have any associated mental-health problems treated.

What benefits can we expect?

"Done properly, the legalisation of cannabis is a win-win-win," says Chris Snowdon of the Institute of Economic Affairs (IEA). "Criminals lose a lucrative industry, consumers get a better, safer and cheaper product, and the burden on the general taxpayer is reduced."

The IEA reckons that Britain's black market is worth £2.6bn a year. If licensed pot comprised the vast majority of the market, and it was taxed at 20% VAT plus a 30% excise tax, £690m would be raised, it estimates. Legalisation also implies new jobs and businesses springing up, generating more tax revenue. The savings to pubic services, meanwhile, would amount to around £300m, says the IEA.

What does the US experience tell us?

Legalised cannabis has provided a welcome fillip for stretched government coffers. Nevada legalised marijuana last summer and derived an instant fiscal boost, drawing $20m in extra tax revenue in just six months. Colorado, the first state to legalise recreational weed, raked in $506m in taxes and fees between January 2014, when sales began, and the summer of 2017. For context, annual government spending in Colorado in 2016 was around $36bn.

A new Canadian excise tax is forecast to yield C$1bn (£580m) in extra federal annual revenue eventually. Canada is also hoping that it can steal an advantage in the growing marijuana business, with Ontario-based Canopy Growth Corporation listed on the New York Stock Exchange and boasting a market capitalisation of almost US$6bn (£4.5bn).

Somewhat surprisingly, the UK also enjoys a strong position in the medical marijuana business despite tough legal restrictions. The UN reported in March that Britain is the world's largest exporter of legal marijuana, mainly due to domestic production of Sativex, a cannabis-based medicine used to treat multiple sclerosis.

So will Britain legalise cannabis?

The recent outcry about medical marijuana has certainly given politicians cause to re-examine rules about what doctors can prescribe to their patients, but wider liberalisation looks unlikely in the short-term.

A YouGov poll in May found three-quarters of the public in favour of medical marijuana, but opinion split down the middle on recreational use, with 43% backing legalisation and 41% opposed. Just 19% of those aged 18-24 support the current arrangements, suggesting that in the long-term Britain may well join the growing global legalisation trend.

However, that appears unlikely so long as Theresa May remains prime minister. A proponent of tough anti-drug policies, during her time as home secretary May pushed through legislation to ban "legal highs" that was so broad that there were fears that even church incense had been outlawed. Still, the momentum in favour of ending prohibition is building globally as the evidence for its failure piles up.