In an analysis of studies on cannabis, the scientists said these
long-term health and life effects were important since several
countries are planning to relax legislation on it.
Cannabis is the most widely used illicit drug worldwide, despite a
trend towards decriminalizing it in some countries.
"Our findings are particularly timely given that several U.S. states
and countries in Latin America have made moves to decriminalize or
legalize cannabis, raising the possibility the drug might become
more accessible to young people," said Richard Mattick, a professor
at Australia's National Drug and Alcohol Research Centre at the
University of New South Wales, who co-led the study.
Using data from three large and long-running studies, the
researchers found that people who smoke cannabis daily before the
age of 17 are more than 60 percent less likely to complete high
school or obtain a university degree.
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The meta-analysis also indicated that daily users of cannabis during
adolescence are seven times more likely to attempt suicide, have an
18 times greater chance of cannabis dependence, and are eight times
as likely to use other illicit drugs in later life.
"Policymakers need to be aware that early use of cannabis is
associated with a range of negative outcomes for young adults that
affect their health, wellbeing, and also their achievements," said
Edmund Silins, also of the National Drug and Alcohol Research
Centre, who presented the findings in a media teleconference.
CLEAR AND CONSISTENT LINKS
Recent data show that young people in some countries are starting to
use cannabis at a younger age than before and that more adolescents
are using cannabis heavily.
In the United States, some seven percent of high-school seniors are
daily or near-daily cannabis users, while in England, four percent
of 11 to 15-year-olds report cannabis use in the past month.
In Australia, around one percent of 14 to 19 year olds are daily
users of the drug, while four percent use it weekly.
Silins said any changes to cannabis legislation should be carefully
assessed to ensure they will help reduce adolescent cannabis use and
prevent its potentially adverse effects.
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The study, published in The Lancet Psychiatry journal, analyzed data
on up to 3765 participating cannabis users in terms of seven
developmental outcomes up to the age of 30 years.
Those factors were completing high school, obtaining a university
degree, cannabis dependence, use of other illicit drugs, suicide
attempts, depression and welfare dependence.
It found clear and consistent associations between frequency of
cannabis use during adolescence and most young adult outcomes
investigated, even after controlling for potential confounding
factors including age, sex, ethnicity, socioeconomic status, use of
other drugs and mental illness.
Importantly, they also noted that risks increased relative to dose,
with daily users showing the strongest effects.
Experts not involved in the research said its findings were
particularly worrying given trends suggesting rising cannabis
consumption.
"This new study ties in well with previous research into the mental
health effects of heavy cannabis smoking during adolescence, a
period where the mind and brain are still developing," said Michael
Bloomfield, a psychiatrist at University College London.
Robin Murray, a professor of psychiatric Research, King's College
London's Institute of Psychiatry said the study "reminds us that it
is important to discourage cannabis use among teenagers, and that
educational campaigns outlining the risks of heavy cannabis use are
warranted whatever (its) legal status.
(Editing by Tom Heneghan)
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