Psychiatrist warns parents of cannabis psychosis link

A leading psychiatrist is warning parents of the clear link between smoking cannabis and psychosis.

Sir Robin Murray, a professor at King’s College London, is concerned that ‘liberal-minded’ parents are so uninformed of the Class B drug’s dangers they grossly underestimate the hazard it poses to mental health.

The most common form of the drug today is skunk, which research has shown was responsible for 94 per cent of the cannabis confiscated by police in five areas of England in 2018 – compared to just over half in 2005.


Sir Robin, who has also worked at the first NHS clinic in England specifically dedicated to cannabis smokers with psychosis, said skunk causes around a third of the psychosis cases he sees, with many of the patients – mostly young people – suffering hallucinations and paranoia.

We’re now 100 per cent sure that cannabis is one of the causes of a schizophrenia-like psychosis

He said: “I think we’re now 100 per cent sure that cannabis is one of the causes of a schizophrenia-like psychosis. If we could abolish the consumption of skunk we would have 30 per cent less patients [in south London] and we might make a better job of looking after the patients we have.”

In 2019, Sir Robin led a research team which found that south London had the highest incidence of psychosis in Europe, and cannabis use was determined to be the largest contributing factor.

Legalisation has failed

The average amount of THC – the chemical compound that gives users a ‘high’ – in cannabis has risen dramatically across Europe and North America, from three per cent in the 1960s to 10-15 per cent today.

legalisation in other jurisdictions such as Colorado has thus far failed to lower the potency of cannabis but makes it more readily available

Despite the evidence, activists are pushing for cannabis to be legalised in the UK.

But Sir Robin pointed to other jurisdictions, such as Colorado, where legalisation has thus far failed to lower the potency of cannabis and makes it more readily available.

De facto decriminalisation

The Times newspaper’s editorial said that the weight of evidence linking serious mental health problems to cannabis “should certainly give pause to those advocating its decriminalisation in Britain”, but pointed out that de facto decriminalisation is already happening by stealth in large parts of the country.

the government must continue to resist pressure to go down the path of legalisation

“Almost a quarter of police forces in England and Wales are allowing drug offenders to escape prosecution, including dealers and users caught with cocaine and heroin, if they sign up to a rehabilitation course.”

It added that it is “essential” that councils “track not only any increase in psychiatric problems associated with cannabis but also any rise in any other drug-related social problems, including road-traffic accidents, street violence and visits to A&E”.

“Meanwhile the government must continue to resist pressure to go down the path of legalisation. One common argument in favour of that approach is it would allow the state to control the quality and strength of cannabis on the market. Yet the experience of Colorado shows the more likely result is that THC levels will soar, with disastrous consequences for young people’s long-term mental health.”

‘Full-blown delusion’

Horatio Clare, a former cannabis user, explained how casual use as a youngster primed him for a psychotic episode as an adult.

“My psyche went off like a bomb. Over the course of two months I rose through hypomania to mania to full-blown delusion. I held wildly fantastical beliefs about conspiracies, world peace, aliens and my crucial role in bringing about a universal evolution of consciousness. After running my car off the road and picking holes in my ceiling I was sectioned and detained in an excellent NHS psychiatric hospital in West Yorkshire.”

every time you catch that reek of skunk, you are smelling life chances burning

Horatio made a recovery and now warns others of the dangers cannabis poses: “According to parents who contact me, it makes special prey of the imaginative, the sensitive and the artistic. You do not know the chamber is loaded for your child until they pull the trigger.”

He added that, though new treatments for psychosis and schizophrenia can be effective, “every time you catch that reek of skunk, you are smelling life chances burning. Of all the mistakes I have ever made, smoking cannabis when I knew it would hurt me was the stupidest.”

Damaged genes

In a letter to The Times, Professor Stuart Reece, of the University of Western Australia, warned that the health risks of cannabis use go well beyond mental health issues, including “damage to both the genes and the complex system that regulates and controls genes”.

He explained that cannabis use can result in “elevated rates of many cancers (testicular, breast, pancreas, thyroid and liver cancers), dozens of birth defects (thalidomide-like affecting the cardiovascular, nervous, chromosomal, digestive and kidney systems) and accelerated ageing of human cells and organisms”.

The professor added: “All of this accelerates exponentially at the higher doses which inevitably accompany cannabis legalisation. Our findings have been confirmed in Colorado, Canada, Australia, Hawaii, the USA and most recently in Europe and can be found via Google Scholar. There is much more to come.”