Smoking cannabis in your teenage years could raise the risk of depression and suicide in later life, a study has found.
Despite calls for it to be legalised and rules relaxed, anti- drug campaigners have long warned about the dangers of cannabis and depression.
Now, researchers of the largest study of its kind have revealed the drug could impair a child’s brain to the extent of triggering mental health disorders later in life.
Over half a million adults in the UK and US could be saved from mental health disorders by avoiding the drug as a teenager.
The researchers have warned that the drug, legal in several US states and used by millions of young people, poses a significant public health risk.
The findings echo previous research evidence findings links between cannabis use and psychosis.
Smoking cannabis in your teenage years could raise the risk of depression and suicide in later life, the largest study of its kind has found
‘It’s a big public health and mental health problem, we think,’ co-author Professor Andrea Cipriani, from the University of Oxford, said.
‘The number of people who are exposed to cannabis, especially in this vulnerable age, is very high and I think this should be a priority for public health and the mental health sector.’
The researchers, at McGill University and the University of Oxford, analysed data from 11 studies involving more than 23,000 individuals.
The study, described as the largest meta-analysis to date in this field, included teenagers who had used cannabis at least once before the age of 18.
About seven per cent of cases of adult depression may possibly not occur if teenagers stopped smoking cannabis, according to the study published in journal JAMA Psychiatry.
This means at any one time up to 60,000 cases among 18 to 34-year-olds in the UK and 400,000 in the US could be attributable to use of the drug during adolescence, they suggest.
However, a link was not found between cannabis exposure and anxiety in adulthood.
While the risk of depression is modest, the researchers said the common use of cannabis among teenagers makes it a concern.
They said it highlighted the importance of educating teenagers about the risks of using cannabis.
Professor Cipriani said: ‘Although the size of the negative effects of cannabis can vary between individual adolescents and it is not possible to predict the exact risk for each teenager, the widespread use of cannabis among young generations makes it an important public health issue.
‘Regular use during adolescence is associated with lower achievement at school, addiction psychosis and neuropsychological decline, increased risk of motor vehicle crashes, as well as the respiratory problems that are associated with smoking.’
The study did not distinguish between the frequency of use in participants.
Ian Hamilton, a lecturer in mental health and addiction at the University of York, told MailOnline: ‘It is difficult to know how much cannabis you would need to use before you develop a problem like depression, what we do know that dose and frequency of cannabis use increase the risk.
‘Researchers usually define regular use as more than fifty times using cannabis or more than once in the last month. But it is possible that the increasing strength of cannabis will increase the risk of developing a problem.’
Cannabis is the most commonly-used drug in the UK, with 6.5 per cent of people aged between 16 and 59 taking it in the past year, which makes up around 2.1million individuals.
In England, about four per cent of adolescents aged 11 to 15 years old in England are estimated to have used the drug within the last month.
In the US, 44 percent of those aged 12 or over have used cannabis at some point in their lives.
Mr Hamilton said although some schools provide drugs education, it often has undesirable effects.
He said: ‘When this has been investigated by researchers it has been shown to backfire, in that this type of well intended education raises interest in cannabis that wouldn’t have happened if the education session hadn’t taken place.’
Recreational use of the class B drug can make a user feel relaxed, and even alleviate depression, anxiety and stress, according to scientific studies.
But its use has been linked to disorders including bipolar, schizophrenia, depression, anxiety, and a negative outlook of social interactions.
WHAT EVIDENCE IS THERE THAT SMOKING 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.