Tolerance of cannabis is growing just as scientists show that it can cause insanity

Supporters of cannabis legalisation are like the tobacco companies denying the link between smoking and cancer

The singer Justin Bieber is promoting pre-rolled cannabis joints that he calls “Peaches”, the name of a song from an album. He is doing so in association with a Los Angeles-based company, Palms Partners, that specialises in selling seven-joint packs for $32 (£24) in California and Nevada. “I’m a fan of Palms and what they are doing by making cannabis approachable and helping to destigmatise it – especially for the many people who find it helpful for their mental health,” he says.

Bieber is one of a strange coalition seeking to legitimise cannabis (marijuana) for its health-giving properties or because they believe that criminalisation has failed and proved counter-productive. Online advertising for recreational cannabis in the US claims that it is an antidote for depression. Amazon, the largest delivery company in the world, is reportedly lobbying in Washington for marijuana’s legalisation at the federal level.

In Britain, the former Conservative Party leader William Hague argues in a newspaper column for a move “from seeing drug use as a criminal issue to a health issue, achieving a crucial change in culture”. He praises Portugal for reclassifying as a misdemeanour the possession and purchase of drugs for individual consumption.

Legalising and commercialising cannabis is well under way from Uruguay to Canada and in at least 10 states in the US. Paradoxically, this shift towards the toleration of cannabis as more or less harmless is taking place just as scientists conclusively prove the link between cannabis and psychosis (a less shocking word than “madness” or “insanity”, but the meaning is the same). Cause and effect is today as well established as it is between cigarette smoking and lung cancer.

“Numerous prospective studies have shown that cannabis use carries an increased risk of later schizophrenic-like psychosis,” says an article by Sir Robin Murray of the Institute of Psychiatry, Psychology and Neuroscience at King’s College London and Wayne Hall of the National Centre for Youth Substance Use Research at the University of Queensland. They cite a study showing that, though Portugal is held up as a pioneer in dealing with drugs, the rate of hospitalisation for psychotic disorders has increased 29-fold since decriminalisation 15 years ago. Another study calculates that between 30 per cent and 50 per cent of new cases of psychosis in London and Amsterdam would not have occurred if the individual affected had not been smoking high-potency cannabis.

Personal observation confirms this: doctors in mental hospitals have told me that they scarcely bother anymore to ask patients if they have taken cannabis, but simply assume it is the case. The situation has deteriorated as the proportion of THC, the psychoactive substance in cannabis producing the “high”, has risen precipitately. Once as low as 3 per cent, it has risen to 10 to 15 per cent in Europe and North America, though in Colorado, the first state to legalise recreational use, the THC can reach as high as 70 per cent. Those taking cannabis daily, particularly if they are young, face an escalating risk of permanent mental breakdown.

But if cannabis has already had its “tobacco moment”, when the damage it does is scientifically proven, why do celebrities like Justin Bieber want to destigmatise it and persuade consumers that it will improve their mental health?

Part of the boosterism in favour of cannabis plugs into its old association with a bohemian lifestyle and “the swinging Sixties”. But it is commercial pressure that is becoming far more important in lobbying for its legalisation. Businesses see they can make money out of it: projected legal sales of cannabis will be worth $66.3bn by 2025, according to a report. Big profits will pay for advertising and lobbying campaigns lauding the drug’s virtues and seeking to put in doubt or divert attention from the harm it causes.

The cigarette industry did this a century ago, funding “independent” experts who sought to blur or discredit evidence that smoking caused cancer. Governments were seduced by high tax revenues from tobacco sales and reluctant to do anything to curtail them. Hollywood stars such as John Wayne, Clark Gable and Spencer Tracy happily – and profitably – glamourised cigarettes, much as is happening to cannabis now.

Businesses seeking to emulate the tobacco companies at the height of their profitability have formed a bizarre de facto alliance with liberals and progressives, who are appalled by the disastrous mess created by government drug policy. The so-called “war on drugs” has demonstrably inflicted more misery in the US, certainly on the black community, than real military conflicts.

But an overreaction to government failure, provoking a dash in the opposite direction, has equal dangers. Those in favour of greater tolerance towards drugs are almost invariably thinking of cannabis as much less nasty than heroin and cocaine. But I have met psychiatrists, with long experience of dealing with drug victims of all sorts, who believe that cannabis is more dangerous than the other drugs because it has the potential to damage many more people.

About 3 million people take illicit drugs in England and Wales, of whom about 2.5 million consume cannabis, some 10 per cent on a daily basis in 2017-18, according to the review of drugs report by Dame Carol Black. Much of the cannabis is produced in the UK, sometimes by Vietnamese organised crime groups using slave labour. Most of the violence provoked by drugs is between the gangs who control the heroin and crack cocaine markets, which are worth about £5bn a year. Decriminalising drugs, notably cannabis, will not affect this sort of battle for territory and market share. Supply lines are very different between the different drug markets, with the heroin from Afghanistan wholesaled by Turkish and Pakistani gangs, and cocaine from Latin America controlled by Albanians.

The legalisation of cannabis will do nothing to hurt organised crime groups, but it will make the drug much more widely available. The idea by proponents of legalisation that the government will tightly regulate its quality and sale is naive. If the authorities cannot control it when it is illegal, they will be even less able to do so when it is legal. But legalisation – and even limited decriminalisation – will send a message that taking cannabis is a benign activity and does not do you or anybody else much harm. The deterrent effect of illegality will evaporate and the drug becomes no different than alcohol and tobacco.

Once commercially available, all the old persuasive tools formerly used by the cigarette industry swing into action as is happening unstoppably in the US. Celebrities like Justin Bieber will “destigmatise” the drug and give it the gloss of youth and fashion. Once, the victims of the tobacco companies coughed up their lungs unnoticed by the wider community, and this time round the victims of cannabis will disappear into mental hospitals without anybody taking much notice.