JUNK MEDICINE: CANNABIS

Science Is No Czar

Fashionable opinion has long held that cannabis is a soft drug with
few risks to health. Its use has become so commonplace that even
those who have not tried it usually have friends and relatives who
have done so without ill effects. Such widespread personal experience
did much to drive the successful campaign to downgrade it from a
class B drug to class C.

There is, however, significant scientific evidence that cannabis is
not always benign. A study from the Karolinska Institute in Sweden
this week found that when rats were exposed to THC -- its main
psychoactive ingredient -- during the equivalent of adolescence,
their brains became more sensitive to heroin. In subsequent
experiments, animals with experience of THC took much more heroin.

The findings lend biological support to the "gateway theory" of drug
abuse, that early cannabis use makes people more susceptible to
heroin addiction later in life. Social factors, and perhaps a genetic
propensity to risk-taking, probably also explain why most heroin
users have experimented with cannabis first. But the notion that
neurological changes in the brain are also important cannot be dismissed.

This is far from the only way in which cannabis can be harmful. It is
estimated that smoking three joints a day carries the same risk of
cancer as 20 cigarettes. More serious still is a link to mental
illness: schizophrenia, bipolar disorder and psychosis.

Scientists have built a compelling case that cannabis can trigger or
worsen these psychiatric disorders. While most people's mental health
will be unaffected by the drug, for some it can have catastrophic
consequences. Robin Murray, of the Institute of Psychiatry, estimates
that as many as 10 per cent of schizophrenia diagnoses can be
attributed to cannabis. The risk may be partly genetic; research by
Avashalom Caspi, a colleague of Murray's, has found that a gene
variant carried by one person in four multiplies the risk of
cannabis- induced psychosis fivefold.

It is no longer possible to contend that cannabis is a safe or mild
drug. Critics of the Government's liberal stance are increasingly
claiming that the science is on their side and they are right that it
gives cause for concern. It does not necessarily follow, though, that
ministers were wrong to reclassify cannabis. Science can offer
valuable guidance, which should always set the baseline for policy
decisions. But though it has a critical place in any sensible debate,
it can contribute only so much.

Science has no view on the most appropriate use of police time and
resources, the chief reason that was advanced for reclassification.
Medical evidence also reveals nothing about the legal strategies that
best dissuade young people from taking cannabis. As Murray says, few
teenagers know whether the drug is classified as class B or C, and
fewer care. And there is a reasonable if unproven argument that
legalisation for adults might be a better way of keeping the drug out
of young hands than giving criminals a monopoly on its sale.

Such a policy might make cannabis less attractive to dealers who
would sell to teenagers, or send a dangerous message that it is safe,
but medical research cannot say which. Evidence suggests that the
young, with still developing brains, are most at risk. That, however,
could support two different approaches: tough age restrictions and
education campaigns about its dangers, or a blanket ban designed to
keep it off the streets.

The choice is ultimately a matter of politics. It is essential that
rigorous, up-to-date research be taken into account when formulating
drug policy, so that risks are considered appropriately. Risks,
however, do not automatically require regulation: they must be
weighed against the costs and benefits of the measures proposed to
control them. Science can inform, but it cannot always decide.