Pubdate: Sat, 08 Jul 2006
Source: Times, The (UK)
Copyright: 2006 Times Newspapers Ltd
Author: Mark Henderson
Note: Mark Henderson is Science Editor of The Times
Bookmark: (Cannabis - United Kingdom)
Bookmark: (Decrim/Legalization)


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.
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