Powerful ‘skunk’ cannabis flooding the streets of Britain increases the risk of psychosis five-fold, a major study has found.
The problem is so widespread that an astonishing 30 per cent of all cases of psychosis in London are caused by the drug, researchers found.
They warned that 94 per cent of all cannabis available on the streets of the UK capital is now of the skunk form.
It is cultivated to have super-high levels of psychoactive THC – making it up to 10 times more powerful than the ‘weed’ and ‘hashish’ more common 20 or 30 years ago.
As much as 94 per cent of all cannabis available from drug dealers in the UK is now skunk, according to the researchers. This form of the drug tends to have higher amounts of THC, the chemical which makes people ‘high’ (stock image)
The King’s College London researchers studied more than 2,100 people in 11 cities in Europe and South America, in the biggest study of its kind ever undertaken.
They found that the link with psychotic disorders such as schizophrenia and paranoid delusion was strongest in London and Amsterdam – the two cities where high-potency cannabis is most commonly available.
Voices for legalisation of cannabis have been growing in recent months, buoyed by the Government’s decision to permit limited use for medical treatment.
The researchers warned against following the lead of Canada and the US states of Colorado and California, where legalisation has seen the potency of cannabis increase even further.
And they said that even medicinal cannabis oil – which is available in the UK for a very limited number of people – should come with a warning of psychosis as a possible side effect.
Professor Sir Robin Murray, one of the researchers on the paper, said: ‘If you are going to legalise – unless you want to pay for a lot more psychiatric beds and a lot more psychiatrists – then you need to devise a system in a way that will not increase the consumption and will not increase the potency.
‘Because that is what has happened in the US states where there has been legalisation for recreational use.’
He added: ‘The critical question is whether medicinal use remains medicinal.
‘The problem in California and Canada was that medicinal use became a synonym for recreational use.
THE DIFFERENCES BETWEEN THC AND CBD
Tetrahydrocannabinol (THC) and cannabidiol (CBD) are both derived from the cannabis plant.
Together, they are part of the cannabinoid group of compounds found in hashish, hash oil, and most strains of marijuana.
THC is the psychoactive compound responsible for the euphoric, ‘high’ feeling often associated with marijuana.
THC interacts with CB1 receptors in the central nervous system and brain and creates the sensations of euphoria and anxiety.
CBD does not fit these receptors well, and actually decreases the effects of THC, and is not psychoactive.
CBD is thought to help reduce anxiety and inflammation.
‘You could go on the internet and tell a doctor “I have headaches, I have back pain, I feel better if I have cannabis.”
‘The main reason they legalised it was to try and control the amount of so-called medicinal use that is being used there, hoping that there would be a decrease in the use.’
He said there was not a risk of that in the UK ‘at present’ because cannabis oil is so strictly controlled.
But be said politicians here should be very cautious and closely monitor the situation on the other side of the Atlantic.
‘Studying animals is very expensive – you have to give them cannabis, you have to feed them, you have to have cages for them,’ Sir Robin joked.
‘But North Americans come free.’
The research team, whose work is published in the Lancet Psychiatry journal, found that skunk – which they defined as having a THC level of more than 10 per cent – increased the odds of psychosis 4.8-fold if smoked every day, compared to someone who never used the drug.
Using it more than once a week was less dangerous, but still increased the risk 1.6-fold.
Low-strength cannabis – that which has a THC level of less than 10 per cent – increased the odds of psychosis 2.2 times if used daily and 1.4 times if used more than once a week.
Study leader Dr Marta Di Forti said the effect of skunk on mental health is so high that in cities where it is widely available it has a huge impact on numbers of people diagnosed with psychotic disorders.
She said if skunk was taken off the streets of London new cases of psychosis would drop 30 per cent, from 46 to 32 cases per 100,000 people.
DOES CANNABIS INCREASE THE RISK OF PSYCHOSIS?
Going from being an occasional marijuana user to indulging every day increases the risk of psychosis by up to 159 percent, research revealed in July 2017.
Marijuana is thought to cause psychosis-like experiences by increasing a user’s risk of depression, a study found. The two mental health conditions have previously been linked.
Frequently abusing the substance also significantly reduces a user’s ability to resist socially unacceptable behavior when provoked, the research adds.
Study author Josiane Bourque from the University of Montreal, said: ‘Our findings confirm that becoming a more regular marijuana user during adolescence is, indeed, associated with a risk of psychotic symptoms.
‘[Psychosis symptoms] may be infrequent and thus not problematic for the adolescent, when these experiences are reported continuously, year after year, then there’s an increased risk of a first psychotic episode or another psychiatric condition.’
The researchers, from the University of Montreal, analyzed around 4,000 13-year-olds from 31 high schools in the surrounding area.
Every year for four years, the study’s participants completed questionnaires about any substance abuse and psychotic experiences.
Psychotic symptoms included perceptual aberration – for example feeling that something external is part of their body – and thinking they have been unjustly badly treated.
The participants also completed cognitive tasks that allowed the researchers to assess their IQ, memory and stimuli response.
This was second only to Amsterdam, where the eradication of skunk would cut psychosis 50 per cent, from 38 to 19 cases per 100,000.
In Cambridge – the only other British city to take part in the study – 8 per cent of psychosis cases were attributed to strong cannabis.
Dr Di Forti said even cannabis oil used for epilepsy and MS – which has very low levels of THC – should come with a warning of possible mental health effects until it is proven that there is no risk.
‘There is no such thing as a medicine which doesn’t come with a side effect,’ she said.
‘That doesn’t stop me prescribing them.
‘But… we should include risk of psychosis in the side-effect profile, both so people that prescribe it can monitor it effectively, and so that people who take it know what to look out for.’
The research comes after another major Lancet study last month concluded that cannabis is responsible for 60,000 cases of depression among young people in Britain.
Psychosis is a much rarer condition than depression – so the numbers affected will be far smaller – but the consequences are generally far more serious.
Voices are growing in Britain for legalisation.
Sir Nick Clegg, the former deputy prime minister, has repeatedly claimed making mild forms of the drug legally available would stop people using skunk.
The All-Party Parliamentary Group on Drug Policy Reform – led by Baroness Molly Meacher – wants sick people to be allowed to grow their own cannabis under licence.
And even the Royal College of Psychiatrists – which for years has warned against legalisation – is currently reviewing its position to take into account the view that decriminalisation would give the government power to both regulate its strength and generate tax from its sale.
Dr Adrian James, registrar of the Royal College of Psychiatrists, said last night: ‘Cannabis carries severe health risks and users have a higher chance of developing psychosis.’
But he added: ‘Because of these risks, a good drugs strategy should focus on preventing and reducing harm, not on diverting people to the criminal justice system.’
Despite agreeing to the limited prescription of medicinal cannabis last year, Theresa May and the Government remain opposed to legalisation.
WHAT EVIDENCE IS THERE THAT CANNABIS INCREASES RISK OF MENTAL HEALTH ILLNESS?
- Schizophrenia: Researchers questioned more than 6,500 teenagers aged 15 and 16 on their cannabis use. They were monitored until the age of 30. Smoking cannabis just five times as a teenager can triple the risk of psychotic symptoms alongside major depression and schizophrenia in later life, according to the study at The Academy of Finland, published in the British Journal of Psychiatry in March 2018.
- Socially unacceptable behaviour: Researchers from the University of Montreal analysed around 4,000 13-year-olds from 31 high schools in the surrounding area for four years. Going from being an occasional marijuana user to indulging every day increases the risk of psychosis by up to 159 percent. Frequently abusing the substance also significantly reduces a user’s ability to resist socially unacceptable behavior when provoked. The research was published in the Journal of Child Psychology and Psychiatry in July 2017.
- Negative emotions: Scientists at the National Institute on Alcoholism and Alcohol Abuse in Bethesda analysed 60 people, half of which were cannabis dependent. The study’s participants completed a questionnaire that asked them about their feelings of stress, aggression, reactivity and alienation. Cannabis users are more likely to experience negative emotions, particularly feeling alienated from others. People who use marijuana are significantly more likely to feel that others wish them harm or are deceiving them. The research was published in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging in January 2018.
- Panic attack reaction: Researchers from the University of Vermont scanned the brains of teenagers in Europe and found just one or two joints is enough to change the structure of a teenager’s brain. It could cause changes affecting how likely they are to suffer from anxiety or panic. Researchers found 14-year-old girls and boys exposed to THC had a greater volume of grey matter in their brains. This means the tissue in certain areas is thicker – the opposite of what usually happens during puberty, when teenagers’ brain matter gets thinner and more refined. The study was published in The Journal of Neuroscience in January 2019.
- Bipolar: Researchers at Warwick Medical School analysed 3,370 women’s cannabis use at 17 years old. At 22-to-23 years old, the participants completed a questionnaire. People who used cannabis at least two-to-three times a week at 17 years old are more likely to experience hypomania in their earlier 20s. Hypomania is defined as elevated mood alongside irritability or an inflated ego, an unrealistic sense of superiority, a reduced need for sleep and frenzied speech. Such symptoms frequently occur in bipolar disorder sufferers. The research was published in Schizophrenia Bulletin in December 2017.