Leigh Dayton, Science writer
November 05, 2005
generation once turned a blind eye to cannabis use,
believing that although the drug was illegal it was also
harmless. The depth of this misconception is hitting home
as evidence mounts that marijuana can - and does - lead to
significant mental health problems.
As reported last week in The Australian, the nation's
crumbling mental health services have exposed a disturbing
link between cannabis use and a host of behavioural and
psychological problems. These range from criminality to
psychiatric conditions such as depression and psychosis, a
group of disorders including schizophrenia that feature
loss of contact with the real world. Think hallucinations,
delusions, paranoia and strange shifting moods.
One expert, Paul
Dillon - information manager of the National Drug and
Alcohol Research Centre at the University of New South Wales
- went so far as damning cannabis use as a "time-bomb"
threatening today's generation of young users.
Dillon is not
alone in pointing a finger at cannabis. Epidemiologist Wayne
Hall - a professor of public health policy at the University
of Queensland - says there is "consistent evidence" that
regular cannabis users double their risk of psychosis from
roughly one in 100, to one in 50.
New and solid
support for an increased risk comes from the Christchurch
Health and Development study. New Zealanders David Fergusson
and his colleagues at the Christchurch School of Medicine
are conducting a long-term, or "longitudinal", study of 1265
New Zealand children. As part of their research, they
gathered data on the frequency of cannabis use and psychotic
symptoms from 1055 of the participants at ages 18, 21 and
In an interim
report published this year in the journal Addiction, the
researchers concluded: "The results of the present study add
to a growing body of evidence suggesting that regular
cannabis use may increase risks of psychosis." They ruled
out the possibility that other unknown factors caused the
worrying association they found.
Fergusson's group also excluded the idea - supported by some
researchers - that people who develop psychotic symptoms
turn to cannabis to relieve their distress, what experts
"The direction of
causality is from cannabis use to psychotic symptoms," they
troubling are other recent findings which suggest that young
users are at particular risk of eventually suffering
psychosis and other mental health problems, claims Hall,
co-author of a comprehensive review of the health and
psychological effects of cannabis use - conducted for the
National Drug Strategy in 2000 - as well as the 2004 update
of the review published in the journal Drug and Alcohol
And users, states
Hall, are starting earlier and earlier: "Over the last 30
years in Australia the age of starting has dropped. Now the
age of initiation is 15 or 16. There's been a big drop in
precocity in a range of behaviours, including alcohol and
Part of the
difficulty facing adolescent users is that today's cannabis
is more potent than yesterday's marijuana. That's so,
according to Dillon, because people are smoking stronger
parts of the plant and doing so in a riskier manner - such
as by bong, or waterpipe.
though, research shows clearly that young brains are at
greater risk than mature ones. Although they've attained 90
per cent of their adult size, adolescent brains are still
growing. They're "plastic", subject to extensive internal
change, explains Murat Yucel, neuropsychologist at the
Melbourne Neuropsychology Centre at the University of
Melbourne. "A lot of wiring and rewiring is occurring," he
says. "The brain is being continuously modelled and is
maturing right through to the early 20s, especially in the
way it is connected." Yucel adds that areas of the brain
integral to regulating emotion and managing memory, along
with thinking, are among those still being shaped during
preliminary findings from brain imaging work that Yucel
conducted with colleagues at the Orygen Research Centre - a
Melbourne University-based mental health service for people
aged 15 to 25 - early cannabis and, to a lesser extent,
alcohol use disrupts "wiring" in parts of the brain vital to
those key functions. The frontal cortex, hippocampus and
amygdala are particularly affected.
It's far from
clear just how dope smoking may impair the formation of
healthy wiring. It may be the abundance of receptors - sites
on brain cells that respond to connection-busting
stimulation by the most active chemical in cannabis,
tetrahydrocannabinol, or THC - in the frontal cortex,
hippocampus and amygdala.
may be that problems emerge because the protective sheaths
that surround brain cells like surgical gloves are not laid
down until the early 20s. "When you introduce cannabis in
moderate to high levels (in adolescence) the connections
(between brain cells) can be damaged," Yucel suggests.
But along with
Hall and other experts, Yucel argues for a multiplicity of
causes, yet to be fully understood. After all, not all young
cannabis users are at equal risk of smoking their way to
poor brain wiring or psychotic illness. Other variables,
from stress to genes, must be cranking up the harm imposed
by heavy and early drug use. Right now, that's precisely
what experts worldwide are trying to sort out.
Yucel and co-workers at Orygen have begun a series of
longitudinal studies involving roughly 400 Melbourne
students now about 14 years old. They've gathered details on
the youngsters' personality, family life and circumstances,
and brain biochemistry, with genetic information to come
"As they start
using substances and developing various disorders - if they
do - we'll know what kind of (factors) are there and how the
onset of mental illness and substance abuse interacted,"
scientific attention is focused on a gene called COMT.
That's so because six years ago international collaborators
- led by psychiatrist Kieren Murphy, of Ireland's Dublin
Molecular Medicine Centre - discovered that a variation of
the gene was associated with psychosis. Tantalisingly, the
gene is involved with a brain chemical called dopamine
which, in turn, influences how a maturing brain is wired.
symptoms, gene, young brain.
Avshalom Caspi, of the Institute of Psychiatry at King's
College, London, teamed with David Fergusson and researchers
at New Zealand's University of Otago in Dunedin to unravel
the clues. Specifically, they wanted to know if COMT is
implicated in the development of psychosis among cannabis
Zealanders were central to the quest. This time the 803
young people studied were part of a group of 1037 children
whose parents had enlisted them as three-year-olds in the
Dunedin Multidisciplinary Health and Development Study, back
in the early 1970s. And again, the scientific sleuths
collected a suite of physical, genetic and social data, and
have followed up the children over the years.
Their verdict on
COMT: guilty as charged.
When they looked
at the well-being of the participants at age 26, Caspi's
group found that if the young people had begun smoking
cannabis in early adolescence, and had the suspect version
of COMT, they were 10 times more likely to have experienced
psychotic illnesses than people who never smoked. That was
even if they had the troublesome version of the gene.
use played a role in the onset of mental disorder, at least
for the Dunedin smokers. But as Caspi's group noted in
Biological Psychiatry in April (2005;57:1117-27), "the vast
majority of young people who use cannabis do not develop
psychosis". They argue that the whole story remains untold.
Part of the story
undoubtedly includes less dramatic elements, ones that are
getting lost in the high-profile discussion of genes,
psychosis and their ilk. "The serious risk that's
underplayed is the risk of dependence, of getting stuck and
finding it hard to quit," says Hall.
"We have people
coming for treatment in their early 30s who've been smoking
for 12 to 15 years who haven't seen it as a problem - until
they try to stop. It's pretty much like alcohol in that
regard," he claims Hall.
Troubling? Indeed. As psychiatrist Ian Hickie argues in
Weekend Health today (see above), it's time to rethink
social attitudes and policy surrounding cannabis use. So
what to do? Hall replies: "Certainly the clearest
implication (of recent findings) is we should be telling
people about risk. No question at all."
But there's been
so much "disinformation" about and "hypocrisy" regarding
cannabis use over the years that young people, in
particular, are turned off by shock-horror health warnings
and heavy-handed tactics, says Hall. "Getting tough and
increasing penalties is likely to be counter-productive."
Getting it right,
putting it in perspective and acknowledging the
inconsistency of prevailing attitudes towards all drugs -
from cannabis to coffee - may be a useful starting point.
As Ian Hickie
suggests, more than one generation should reconsider the
realities of reefer madness.