Teenagers who frequently smoke cannabis tend to do worse in exams, a large study of British schoolchildren has found.
Adolescents
who have smoked cannabis 50 times by the age of 15 show ‘impaired’
educational abilities, according to a study by University College
London.
The
impact of lighter cannabis use is hard to discern, the researchers
found, because it is difficult to isolate the different influences of
rebellious teenage behaviour such as drinking, smoking and other drug
use.
Teenagers who have smoked cannabis 50
times by the age of 15 show 'impaired' educational abilities and do
worse in their GCSE exams, researchers found
The
findings, presented at a science conference in Berlin, add to a growing
weight of evidence that suggests cannabis is more harmful than
legalisation campaigners would have us believe.
Last
week a review of 20 years of cannabis research, published by a
professor at King’s College London, revealed that one in six teenagers
who use cannabis become dependent on the drug, as do one in ten adults.
The King’s College review also suggested that cannabis may cause mental health problems and can open the door to hard drugs.
The
risk of developing psychotic disorders including schizophrenia doubles
with heavy cannabis use in the teenage years, it found.
The new study focuses on the educational attainment of teenagers who smoke cannabis.
Researchers analysed data from 2,235 children from Bristol.
The
information, taken from the Avon Longitudinal Study of Parents and
Children project, follows the health of children born in 1991 and 1992.
The
participants each had their IQ tested at age 8 and again at 15, when
they also completed a study on cannabis use and other lifestyle factors.
The IQ results were correlated with their GCSE results a year later to see what impact the drug had on exams.
The
researchers could find no link between light cannabis use and their
exam results, mainly because there was no way to pull apart the various
impacts on exam scores.
Negative
behaviour such as drinking, smoking and other drug use each had an
impact on exams, so there was no method of isolating the impact of light
cannabis use.
But
they found that the impact of heavy cannabis use was so significant
that they were able to pick it out despite the other factors.
Those
who had smoked cannabis more than 50 times before they were 15 did
distinctly worse in their GCSEs - with an average 3 per cent results
drop - even after adjusting for previous educational performance,
alcohol, cigarette and other drug use.
Drinking, smoking and other drug use
each had an impact on exams, but there was no way of isolating the
effects of light cannabis use. Heavy cannabis use was so significant
that researchers were able to pick it out despite the other factors
Lead
researcher Claire Mokrysz, who presented her results at the congress of
the European College of Neuropsychopharmacology in Berlin, said:
‘Adolescent cannabis use often goes hand in hand with other drug use,
such as alcohol and cigarette smoking, as well as other risky lifestyle
choices.
‘It’s
hard to know what causes what - do kids do badly at school because they
are smoking weed, or do they smoke weed because they’re doing badly?
This study suggests it is not as simple as saying cannabis is the
problem.’
But
she added: ‘The finding that heavier cannabis use is linked to
marginally worse educational performance is important to note,
warranting further investigation.’
The
chair of the congress, Prof Guy Goodwin of the University of Oxford,
said: ‘This is a potentially important study because it suggests that
the current focus on the alleged harms of cannabis may be obscuring the
fact that its use is often correlated with that of other even more
freely available drugs and possibly lifestyle factors.
‘These may be as or more important than cannabis itself.’
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