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Smoking just one cannabis joint raises danger of mental illness by 40%
By FIONA MACRAE and EMILY ANDREWS
A single joint of cannabis raises the risk of schizophrenia by more than
40
per cent, a disturbing study warns.
The Government-commissioned re****t has also found that taking the drug
regularly more than doubles the risk of serious mental illness.
Overall, cannabis could be to blame for one in seven cases of
schizophrenia
and other life-shattering mental illness, the Lancet re****ts.
The grim statistics - the latest to link teenage cannabis use with mental
illness in later life - come only days after Gordon Brown ordered a review
of the decision to downgrade cannabis to class C, the least serious
category.
The Prime Minister is said to have a 'personal instinct' that the change
should be reversed, with more arrests and stiffer penalties for users.
Cannabis has been implicated in a string of vicious killings, including
the
recent stabbing of fa****on designer Lucy Braham.
The authors of the latest study, the most comprehensive of its kind and
commissioned by the Department of Health, said: 'Policymakers need to
provide the public with advice about this widely-used drug.
'We believe there is now enough evidence to inform people that using
cannabis could increase their risk of developing a psychotic illness later
in life.'
The analysis does not look at the age at which schizophrenia is likely to
develop. However, previous studies have shown that smoking the drug as a
teenager raises the risk of developing schizophrenia in one's twenties or
thirties.
The researchers, from four British universities, analysed the results of
35
studies into cannabis use from around the world. This suggested that
trying
cannabis only once was enough to raise the risk of schizophrenia by 41 per
cent.
At greatest risk, however, were heavy users, with those who took cannabis
over 100 times having more than double the risk of those who never touched
the drug.
With up to 40 per cent of teenagers and young adults in the UK believed to
have tried cannabis, the researchers estimate that the drug could be
behind
14 per cent of cases of schizophrenia and other psychotic illnesses.
'Although individual lifetime risk of chronic psychotic disorders such as
schizophrenia, even in people who use cannabis regularly, is likely to be
low - less than three per cent - cannabis use can be expected to have a
substantial effect on psychotic disorders at a population level because
exposure to this drug is so common.'
Cardiff University researcher Dr Stanley Zammit added: 'Even if cannabis
does cause an increased risk of developing psychosis, most people who use
cannabis will not develop such an illness.
'Nevertheless, we would still advise people to avoid or limit their use of
this drug, especially if they start to develop any mental health symptoms,
or if they have relatives with psychotic illnesses.'
In an accompanying editorial in the Lancet, Dutch psychiatrists said the
focus on heroin, cocaine and other Class A drugs meant the dangers of
cannabis had been overlooked.
'In the public debate, cannabis has been considered a more or less
harmless
drug compared with alcohol, central stimulants and opioids.
'However, the potential long-term hazardous effects of cannabis with
regard
to psychosis seem to have been overlooked, and there is a need to warn the
public of these dangers, as well as to establish a treatment to help young
frequent cannabis users.'
Previous studies have shown a clear link between cannabis use in the
teenage
years and mental illness in later life.
Research completed by leading psychiatrist Professor Robin Murray in 2005
showed that those who smoked the drug regularly at 18 were 1.6 times more
likely to suffer serious psychiatric problems, including schizophrenia, by
their mid-20s.
For those who were regular users at 15, the stakes were even higher, with
their risk of mental illness by the age of 26 being 4.5 times greater than
normal.
It is thought that, used during teenage years, the drug can cause
permanent
damage to the developing brain.
Professor Robin Murray, of the Institute of Psychiatry in London, warned
yesterday that the risks were likely to be heightened by the increasing
use
of powerful skunk cannabis.
'My own experience suggest to me that the risk with skunk is higher.
Therefore their estimate that 14 per cent of cases of schizophrenia in the
UK are due to cannabis is now probably an understatement.'
Marjorie Wallace, chief executive of the mental health charity SANE, said:
'This analysis should act as a serious warning of the dangers of regular
or
heavy cannabis use, doubling the risk of developing schizophrenia - a
condition in which a person may hear voices and experience strange
thoughts
and paranoid delusions.
'The debate about classification should not founder on statistics but take
into account the potential damage to hundreds of people who without
cannabis
would not develop mental illness.
'While the majority can take the drug with no mind-altering effects, it is
estimated that 10 per cent are at risk.
'You only need to see one person whose mind has been altered and life
irreparably damaged, or talk to their family, to realise that the
headlines
are not scaremongering but reflect a daily, and preventable, tragedy.'
However, others questioned the link, pointing out there has been little
change in rates of schizophrenia in recent years despite the rise in
cannabis use and the increasing strength of the drug.
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