Urgent warning over cannabis as UK's top psychiatrist warns it isn't safe for young brains still developing
By Xantha Leatham
Daily <ail
Oct 26, 2025
Many parents still think cannabis is relatively safe for their children to have, Dr Lade Smith warned, and called on the government to raise awareness of the potential harms
It may seem like a relatively harmless right of passage.
But cannabis isn't safe for young brains still developing, the UK's top psychiatrist has warned.
An aggressive cannabis lobby is making parents complacent about the risks the drug poses to teenagers' mental health, Dr Lade Smith, president of the Royal College of Psychiatrists, said.
And taking up the habit could damage the brain or even trigger psychotic episodes later in life, she cautioned.
'When you start smoking with your mates at 14 or 15 you are literally growing your brain in a cannabis soup,' Dr Smith told The Sunday Times.
'There's no doubt at all. Cannabis is a cause of psychosis.'
This health condition is a serious mental illness where a person loses touch with reality, often involving symptoms like hallucinations and delusions which can cause them to pose a danger to themselves or others.
Figures show cannabis is consistently the most consumed illegal drug in England and Wales, with 2.3 million people estimated to have used it in the year to March 2024.
Research, published last year, shows adolescents who used it were 11 times more likely to have a psychotic episode as an adult.
However, many parents still see it as relatively safe, Dr Smith warned, calling on the government to do more to educate parents and young people.
'We've not got the public health message right,' she said. 'We know that cannabis is not a safe option.'
She explained that – as well as psychosis – smoking cannabis is also linked to a higher risk of anxiety and depression.
Children from any walk of life, including from well–to–do families, have developed psychotic illnesses, carried out dangerous stunts or fallen foul of the police due to their cannabis use, she warned.
A study published in the journal JAMA Psychiatry found that rates of first episode psychosis are higher in southeast London, where she works, than anywhere else in Europe.
A staggering 97 per cent of patients in her service had a substance abuse problem, with high–strength cannabis the main drug of choice.
The cannabis that has been available in the last 10–15 years in the UK is high–strength, meaning is contains high levels of the active compound tetrahydrocannabinol (THC) which affects the brain.
It can interfere with the release of dopamine in the brain's reward centre, reduce the amount of grey matter in the brain, lower inhibitions and cause chronic bronchitis symptoms.
Smoking cannabis 'regularly' is the equivalent of just one spliff per week, Dr Smith explained, adding that having a problem with the drug 'could completely ruin your life'.
Seven years ago the law was changed to allow the prescriptions of cannabis–based medicines that include cannabidiol (CBD), which does not give the same high but can still alter consciousness and the perception of pain.
Dr Smith said she believes the use of cannabis as a medicine should face further scrutiny. Sir Chris Whitty, the chief medical officer, also warned against 'cannabis exceptionalism' in 2019.
Separate studies have also indicated that cannabis use can negatively impact female fertility and lead to increased levels of paranoia.
Speaking previously about the effects of cannabis on mental health Dr Emily Finch, chair of the Royal College of Psychiatrists' Addiction Faculty, said: 'Society must be more aware of the substantial evidence on cannabis harms, and correct the widespread misapprehension that cannabis is not an addictive substance.
'Cannabis is the most widely used illicit substance in the UK, and around a third of people who use cannabis develop a problem with the drug at some point during their lives. This is similar to the proportion of people who will develop a problem with alcohol.
'The use of both natural and 'synthetic' cannabinoids over the long–term risks addiction and severe co–occurring mental illness harms.'
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.
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