Research has shown that cannabis use
by young teenagers can lower their intelligence and may cause permanent mental
impairment.
Researchers
from Britain and the US found that persistent and dependent use of cannabis
before the age of 18 may have a so-called neurotoxic effect, but heavy use
after 18 appears to be less damaging to the brain.
The
most persistent users suffer an average eight-point decline in IQ between
adolescence and adulthood, according to the study of more than 1,000
participants.
Scientists
believe smoking cannabis from the age of puberty may disrupt developing and
vulnerable brain circuits.
The
study, which was published in the Proceedings of the National Academy of
Sciences, revealed that users experienced significantly more attention and
memory problems than non-users.
Quitting
or cutting down on cannabis use later in life did not fully reverse the impact
on those who started taking the drug in their early teens.
The
study found no evidence of similar problems affecting people who only took up
cannabis as adults.
Professor
Terrie Moffitt at King's College London's Institute of Psychiatry said the
scope and length of the study gave its findings added weight.
Prof
Moffitt worked with Madeline Meier, a post-doctoral researcher at Duke
University, to analyse data on 1,037 New Zealanders who took part in the study.
About
96% of the original participants stuck with the study from 1972 to today, she
said.
At
age 38, all participants were given a battery of psychological tests to assess
their memory, processing speed, reasoning and visual processing.
Those
who had used cannabis persistently as teens scored significantly worse in most
of the tests.
Friends
and relatives regularly interviewed as part of the study were more likely to
report that the heavy cannabis users had attention and memory problems such as
losing focus and forgetting to do tasks.
Previous
research on cannabis use has also pointed to potential long-term psychiatric
effects.
A
study published in March last year found that people who use it a lot in their
youth dramatically increase their risk of psychotic symptoms, and that
continued use of the drug can increase the risk of developing a psychotic
disorder.
SOURCE: http://www.rte.ie/news/2012/0828/research-cannabis-teenagers.html
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