AN EPIDEMIC OF CANNABIS USE?

Dr Raj Persaud Warns Against the Dangers of an Epidemic of Cannabis
Use - Which He Argues Could Have Explosive Effects on the Nation's
Mental Health

An enigma which frequently clouds the cannabis debate is - if it's as
dangerous as doctors and scientists claim - how come despite being
possibly the most used illicit drug worldwide, the ill effects appear
to affect so few?

For example surveys suggest that as many as one in four of those aged
from the late teens to the early twenties in the UK admit to having
smoked cannabis recently -- yet the rate of schizophrenia remains
relatively but stubbornly low in comparison -- roughly one in a hundred.

Previously the debate over the dangers of cannabis had focused on
other controversial areas such as how dependency inducing it was and
what was the physical damage, but now psychiatrists in particular are
concerned at the accumulating evidence cannabis produces devastating
effects on mental health in the form of psychosis.

As far back as 2002 a large-scale study of more than 50,000 men
conscripted into the Swedish army between 1969 and 1970 suggested
that those who had used cannabis more than 50 times before the age of
18 years had an almost sevenfold increased risk of developing
schizophrenia in later life. In a New Zealand study published at the
same time, those who started cannabis use by age 15 years (but not
those who started later) showed a fourfold increase in the risk of
developing schizophrenia-like illness by age 26 years.

So one possible answer to the enigma of widespread use combined with
apparently low incidence of mental health effects is that it could be
the age at which you start smoking that is a crucial mediating factor.

We know the adolescent brain is developing rapidly and could be
particularly vulnerable to damage if psychoactive substances are
imbibed during a 'critical period' or 'window' of brain development.

Another possible answer is that smoking cannabis if you are
genetically predisposed to psychosis produces a very different mental
health outcome compared to if you have a contrasting genetic template.

The genes load the gun but it's the cannabis which pulls the trigger.
Given you don't know your own genetic endowment (the blood test is
only available at some specialist research centres including the
Institute of Psychiatry in London), smoking cannabis is lot closer to
playing Russian Roulette than many realise.

To summarise a wealth of data from all over the world: cannabis use,
whatever your age of smoking, is associated with a general twofold
increase in later schizophrenia, but adolescent-onset cannabis use is
associated with a much higher risk.

Professor Robin Murray, from the Institute of Psychiatry, has
recently attempted to simplify the statistics. In the most recent
comprehensive review of the research he estimates that the
elimination of cannabis use in the UK would reduce the incidence of
schizophrenia by approximately 8 per cent.

That figure might dramatically change if cannabis use goes up, even
more strikingly if it increases in the young. Ominously the number of
cannabis users seeking treatment has doubled in the past 10 years in the UK.

Trends of cannabis use among adolescents indicate that use under the
age of 16 years is a fairly new phenomenon that has appeared only
since the early 1990s. One would therefore predict an increase in
rates of schizophrenia in the general population over the next 10 years.

Indeed, there is already some evidence that the incidence of
schizophrenia is currently increasing in some areas of London,
especially among young people, argues Professor Murray in his recent review.

But in a sense all the statistics or data in the world may make
little difference to the cannabis debate for one key psychological
reason -- we have a natural human tendency to be poor at assessing
risk when its presented to us in the form of numbers or data. Our
brains are wired up much more to making decisions over risk in actual
real world situations -- we make assessments from our direct experience.

Few will directly experience psychosis either in themselves or others.

Even those we are in daily contact with, friends and relatives, if
they develop severe mental illness they may not advertise it. Part of
the direct purpose of mental health services is to offer privacy and
efficient treatment away from prying eyes -- so the taboo surrounding
the area conspires to ensure we are only dimly aware of the true
mental health of our neighbours or colleagues.

The actual hazards of cannabis are therefore become difficult to
engage with if we are using our direct experience particularly if
that is of several acquaintances using the drug apparently without
ill effect. Another intriguing social psychological effect comes into
play here and that is our tendency to select our friends and
acquaintances so that they in turn may assist us with choices we are
already predisposed to take.

For example it was previously thought that peer pressure played a
considerable role in determining which adolescents ended up taking
drugs and which desisted successfully. Falling in with a 'bad crowd'
could be fatal in this respect.

Yet the latest research now suggests that actually the mechanism by
which a drug abuse pathway in life is followed is more complicated
than that. It turns out we appear to select our friends in a way that
reflects our personality. So, for example, risk takers tend to choose
other risk takers as friends, and it's this interaction between them
and our own predisposed personality, which results in the drug taking
behaviour, amongst other outcomes.

So its not that we fall in with the wrong crowd -- more that we
choose the wrong crowd because at some level their choices appeal to us.

This has an important lesson for us -- when we assess risk -- as in
say the cannabis debate -- perhaps we should assess our social
environment as well as its this direct experience -- not the
statistics -- which will most influence us. Have we chosen to be
surrounded by those whose own choices will merely reinforce our own?

Sometimes the best way to improve our decision-making is to actively
seek out and experience those aspects of the debate we may tend to
avoid because it may be inconvenient to our own accepted outlook.

For this reason I just wish it was possible for more to experience my
own ward at the Bethlem Royal and Maudsley NHS Hospitals Trust where
cannabis abuse appears an epidemic and has lit a fuse the explosion
from which, in the form of possibly dramatic higher rates of
schizophrenia in the near future, could have massive fall out --
affecting us all.