People who regularly smoke cannabis 'are nearly three times more likely to be violent', study finds
By Stephen Adams
The Mail On Sunday
June 7, 2020
People who regularly smoke cannabis are
almost three times more likely to commit a violent offence as those who
abstain from the drug, new research has found.
Scientists
involved in a landmark study of almost 300,000 teenagers and young
adults believe that over time, prolonged cannabis use profoundly alters
the brain, making the user less able to control their temper.
In
addition, the research found addicts may also suffer from withdrawal
symptoms, making them irritable and prone to lashing out.
Psychiatrist
Professor Sir Robin Murray, a world-leading expert on the neurological
impact of the drug, said the link between cannabis use and violence was a
‘neglected area’.
Commenting on the study’s findings, he
said: ‘This is not a surprise for those of us who follow the scientific
literature or see patients who heavily use cannabis.
‘However, it may be a surprise to the many who think cannabis is a chill-out, anti-violence drug.’
Britain has been plagued by a succession of brutal killings linked to cannabis in recent years.
In
some of the cases, lawyers have argued the perpetrators should not be
found guilty of murder because they were suffering from psychosis, a
mental condition now understood to be exacerbated by smoking strong
cannabis.
Among the killers was student
Femi Nandap, who, in December 2015, stabbed public health expert Jeroen
Ensink to death outside his home in North London.
Mr Ensink, 41, had popped out to post cards announcing that his wife Nadja had given birth to their daughter.
Forensic
psychiatrist Dr Samrat Sengupta, of Broadmoor Hospital, told the Old
Bailey that the student’s heavy cannabis habit had triggered a genetic
psychotic illness.
Nandap, then 23, was given an indefinite
hospital order after admitting manslaughter on the grounds of diminished
responsibility.
The researchers
decided to examine 30 individual studies examining the link between
cannabis use and violence because ‘the [scientific] literature has shown
that cannabis use may lead to violent behaviours and aggression;
however, this association has been inconsistent’ – with some studies
showing a relationship and others not.
The
team from Montreal University in Canada discovered 26 of the 30 studies
showed a tendency towards higher levels of violence among cannabis
users.
When they pooled the results –
meaning they were looking at a combined group of 296,815 teens and
adults under 30 – they found users were more than twice as likely (2.15
times) to have committed a violent offence as non-users.
Among ‘persistent heavy users’, the risk of violence was 2.81 times higher.
Writing in the American Journal Of
Psychiatry, they said: ‘This study suggests that cannabis use appears to
be a contributing factor in the perpetration of violence.’
Even
when accounting for different life circumstances which might mean
cannabis users were more likely to grow up in violent surroundings, they
concluded that ‘the effect remained significant’.
Citing
neurological research, they said cannabis use during adolescence ‘may
cause deterioration of neural structures associated with inhibition and
sensation-seeking’, adding: ‘Such neural deficits are expected to limit
one’s ability to suppress the urge to act out violently and heighten the
risk of developing antisocial behaviours in adulthood.’
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