CANNABIS RISKS MUST NOT BE UNDERPLAYED

Professor David Nutt Is Wrong. We Cannot Compare Smoking The Drug With
Using Cigarettes Or Alcohol

The ill-tempered argument over cannabis use is an ideological dispute
between those who regard it as an entirely safe herb and those who
regard it as a devilish drug likely to drive one mad after a few
puffs. Sadly, there is rarely an honest and open discussion on why
people enjoy it, what level of consumption is safe, if adolescents are
especially at risk and whether certain types of cannabis pose greater
dangers.

Professor David Nutt, who was sacked as the Government's drugs
adviser, claims that cannabis is no more dangerous than alcohol or
cigarettes. But is it sensible to equate even these two? There are no
health benefits in smoking cigarettes, which is simply a manifestation
of nicotine addiction. Most adults in Britain, however, drink alcohol
in moderation, and suffer few adverse consequences. Yet most know that
drinking a bottle of vodka a day is likely to harm their health, and
few favour daily drinking from the age of 14.

There is a lot of evidence that smoking several joints a day impairs
memory. Using brain imaging, cannabis can be seen to impair the
function of the hippocampus, a structure essential to memory. If we
drink heavily for an evening, we may remember little the next day. But
alcohol is washed out of the system in 24 hours; cannabis can be
detected a month later. No wonder the academic performance of school
children who smoke it daily deteriorates; they have a chronic
low-grade intoxication.

It remains disputed whether memory returns totally to normal after
consumption ceases. In those who have smoked only for a few months or
years, there is every hope of a return to normality in months. But
whether a "stoner" addled by decades of consumption can regain all his
faculties remains uncertain.

People with schizophrenia use more cannabis than the general
population; that is undisputed. The critical question is whether
cannabis use has helped to cause it. Evidence has been mounting
steadily over the past six years that initially healthy people who use
cannabis daily are more likely to develop paranoia and psychosis.
Those with a family history of mental illness, with a suspicious or
psychosis-prone personality and those who start cannabis use in early
adolescence appear at greater risk.

It is not surprising that the link between cannabis and schizophrenia
remains controversial. It took several decades for society to accept
that smoking tobacco increases the risk for lung cancer. Now it is
generally accepted. In his lecture last week Professor Nutt contrasted
a 2.6-fold increase in the risk of psychosis from using cannabis with
a twentyfold increase in the risk of lung cancer if one smokes
cigarettes. Unfortunately he was not comparing like with like here.
The twentyfold increased risk does not come just by being a smoker but
by being a long-term heavy smoker. For cannabis, the risk of
schizophrenia rises about sixfold if one is a long-term heavy user.

Nevertheless, 90 per cent of daily users will not develop
schizophrenia, just as most daily smokers will not die of lung cancer.
But even among those who never come near a psychiatrist, daily
cannabis users are more likely to be unsuccessful in their careers, to
have broken marriages and to suffer minor psychological problems such
as anxiety and depression. For teenagers and their families the
consequences of cannabis smoking may never register in medical
statistics, yet be devastating in their impact on family life.

In 2007 the Advisory Council on Misuse of Drugs concluded that street
cannabis was getting more potent, a view confirmed by two large
surveys. These showed that the concentration of THC, its main active
ingredient, had increased from about 4 per cent in 1970s resin to
14-18 per cent in present day skunk.

Giving THC to normal volunteers in a laboratory setting induces
psychotic symptoms to a varying extent, depending on the dose.
Cannabis is a complex substance and THC is not the only
constituent.

Another is cannabidiol (CBD), which does not induce psychosis in
studies; if anything it relieves anxiety, and may even have
antipsychotic effects. Traditional cannabis resin contains equal
amounts of THC and CBD, so some pro-psychotic effects of THC may be
counterbalanced by the CBD. In skunk, not only has the concentration
of THC greatly increased but the CBD has virtually disappeared, so it
may carry a double whammy. Skunk's ever-larger share of the street
market is worrying.

There is little evidence that altering the legal classification of
cannabis affects consumption. When the law was liberalised in 2004
cannabis consumption was falling in most of Western Europe, and the UK
has followed the general trend.

Two Western European countries with markedly different policies have
less of a problem than the UK. The Swedes adopt a prohibitionist line
and only about 8 per cent of adolescents have smoked cannabis. The
Dutch have a very liberal policy and 28 per cent of adolescents use
cannabis. Both have lower consumption than the UK where 38 per cent of
16-year-olds have used it. Teenagers starting to use cannabis do not
debate its exact classification; many do not even think it is a drug
and few have any knowledge of its hazards. What does appear to have an
effect is knowledge about the risks of heavy consumption.

Rather than arguing whether cannabis should be a Class B or C drug,
politicians would be better to support a big educational campaign on
the properties and constituents of different types of cannabis and the
risks associated with heavy use.

Robin Murray is Professor of Psychiatric Research at the Institute of
Psychiatry, King's College London