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What do health experts, criminal justice practitioners and political thinkers say is the best way forward on cannabis? Do any of the legalisation models we have reported on so far in our investigation into cannabis reform — Canada, Colorado, California or Uruguay — convince them? The Evening Standard asked if the supply and consumption of cannabis should be legalised, decriminalised or left as it is? All backed either decriminalisation or legalisation, with support for the latter subject to control over the strength of intoxicating THC and its ratio to non-intoxicating CBD.

‘Cannabis makes depressed people even more depressed’

Morris Zwi

Consultant adolescent psychotherapist, formerly with Whittington Health NHS Trust

I worked for 33 years in the NHS, mostly with teenagers suffering from depression, anxiety and challenging behaviour, and I saw that teenagers who use cannabis to self-medicate for depression usually become more depressed. I like the way they decriminalised cannabis in Portugal because it allows dependent users to seek medical help. Legalisation would bring advantages because cannabis would be labelled and people would know what strength they’re taking, and with that information I could wean them off. My worry is whether full legalisation would lead to a rise in use among young people, though reassuringly that hasn’t happened so far in Colorado or Canada. We probably need more time to assess the impact in Canada. On the other hand, keeping cannabis illegal keeps it in the hands of criminals, the least safe option. For these reasons I feel divided.

Verdict: Decriminalise and seek more evidence on legalisation in Canada

‘Rise of concentrates with 80% THC potency was unexpected in US’

Tom Freeman

Psychopharmacologist, University of Bath

Legalisation could make cannabis use safer by replacing high THC/low CBD cannabis that currently dominate illicit markets with safer low THC/high CBD forms of cannabis. However, in parts of the US where they have legalised, there has been a rise in cannabis with higher THC concentrations (15-20 per cent) that could carry greater risks. What’s more, about 20 per cent of cannabis sales are newer products called concentrates, which can have over 80 per cent THC. This outcome was not anticipated in the US. To make cannabis use safer, products could be taxed according to THC content. Additionally, guidelines based on THC and CBD consumption could help people use cannabis more safely, in the same way that alcohol units can help people minimise the harms of drinking.

Verdict: Legalisation and regulation of THC and CBD content is preferred

‘Cannabis is less harmful than alcohol but not without risks’

Wayne Hall

Professor at Centre for Youth Substance Abuse Research, University of Queensland and visiting professor at National Addiction Centre, King’s College London

The current system seeks to reduce cannabis consumption by criminalising use and is hard to defend as effective or fair. Legalising it would reap clear economic advantages because we could bring it into the regular economy and tax it. The downside is that once you create a legal industry, its interests lie in increasing daily use and that could mean rising mental health harms and more young people becoming dependent. That hasn’t happened in Canada or the US so far, which is reassuring. I think there’s a real chance legalisation will happen in the UK in the next 10 years. Cannabis is not as harmful as alcohol, but it is not without its risks.

Verdict: Qualified support for legalisation

‘Criminalisation has not worked and is a waste of police resources’

Ron Hogg

Durham Police and Crime Commissioner

In my 40 years experience in the force, three things have changed radically: the harm of cannabis has increased, revenue going to organised crime groups has never been higher (over £2.5 billion) and violence around drugs has risen. The War on Drugs has failed and unless we want to arrest three million people, we need a new approach.

I have written to the Home Secretary Sajid Javid calling for a thorough debate on cannabis strategy and for government to arrange fact-finding missions to Colorado, Uruguay and Canada. Each has a different system: free market in Colorado; state control in Uruguay; public health in Canada.

In Durham, we no longer pursue people for possessing or smoking cannabis. We’re on the right side of history, but history, it seems, still has a way to go.

Verdict: Legalisation coupled with regulation will reduce harm

‘10 hours on my police shift: how do people want me to spend it?’

Simon Kempton

Operational policing lead, Police Federation (represents rank and file officers)

We changed our policy as a federation 12 months ago to say prohibition has not worked.

The question I put to the public is this: if I’ve got 10 hours on my shift, how do you want me to spend it? Chasing serious criminals or people who smoke cannabis? The question I ask myself is: what action would make my daughter at university safer? Prohibition has made her less safe because it’s more difficult to have an honest discussion around drugs.

Prohibition gives us black markets and black markets give us skunk and contaminated drugs and sadly people die from that. We reduced the number of people who smoke cigarettes, not by making them illegal, but by education and letting people make their own judgment. We need a fresh public debate. We should start by looking to how Canada has prioritised education and public health to make cannabis legal but less harmful.

Verdict: Criminalisation has failed and discussion on legalisation is overdue

‘Only way to get rid of skunk, make cannabis safer is to legalise’

Baroness Meacher

Crossbench peer and co-chairwoman of all-party parliamentary group on drug policy reform

The latest 2019 research by Marta Di Forti at King’s College London concluded that low-potency cannabis has no increased likelihood of psychotic episodes compared to those who never used cannabis. There is also a growing body of research challenging the causal link between cannabis and psychosis. A 2018 study says the causal effect is the other way and a Swedish study says it’s familial risk and not cannabis that causes schizophrenia.

Criminalisation has been a disaster for young people, giving them criminal records and driving up use of ever stronger cannabis known as skunk. The only way to get skunk off our streets and make cannabis safer is to legalise and regulate cannabis to limit potency, specifying a maximum ratio of THC to CBD. The whole motivation of the law should be to create a safer world for young people.

Verdict: Legalise and regulate potency

‘Let’s decriminalise and see what happens’

Daniel Hannan

Conservative MEP, a founder of Vote Leave, and editor-in-chief of The Conservative, a journal of centre-Right political thought

We should decriminalise cannabis for a two-year trial period and then, having seen the evidence, hold a vote in Parliament on whether to make that change permanent. A bit like when we experimentally changed British Summer Time. Only then should we think about legalising as decriminalisation still leaves drug supply in the hands of criminals.

Verdict: Decriminalise