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Comment: Exaggerated claims are no basis for policy

Gordon Brown has made his position on cannabis crystal clear but, if the reports are right, the Advisory Council on the Misuse of Drugs is not minded to take the hint. Nor should it.

This is a political row fuelled by the Prime Minister's anxiety to pacify Middle England. There is a widespread, but mistaken, belief that the country is in the grip of an epidemic of cannabis-induced psychosis. This is based on the conviction that the cannabis sold on the streets is a lot stronger than it was a generation ago and is tipping some people into schizophrenia.

The council's review of the scientific evidence underpinning the classification of cannabis is the second in two years. Mr Brown ordered it as a means of distancing himself from his predecessor and has said he would like to see the decision to downgrade the drug to class C reversed.

That decision, taken by David Blunkett in 2004 when he was Home Secretary, was meant to free up police time squandered on prosecuting users. Mr Brown believes it sent the wrong message to young people. Yet use of the drug has fallen since it was downgraded.

Fears about the drug have been fuelled by reports that some of the "skunk" on sale is up to 30 times stronger than ordinary cannabis. Skunk actually contains 10 to 14 per cent of tetrahydrocannabinol (THC) compared with 2 to 4 per cent in herbal cannabis.

Claims about the dangers of cannabis are also exaggerated. An estimated 80 per cent of people with schizophrenia smoke cannabis. Many mental patients self-medicate with cannabis, which can aggravate their symptoms. But this is different from saying cannabis causes schizophrenia. In its last review in early 2006, the advisory council concluded: "The evidence suggests, at worst, that using cannabis increases the lifetime risk of developing schizophrenia by less than 1 per cent."

Some scientists, notably Professor Robin Murray of the Institute of Psychiatry, have argued this underplays the risks to a small minority who are prone to paranoid thoughts. But according to reports, research from Keele University found that rising cannabis use over the past 30 years had not been accompanied by a rise in schizophrenia.

That suggests there is no scientific basis for altering the council's 2006 conclusion that cannabis is "substantially" less harmful than the Class B drugs amphetamines and barbiturates. If the classification system is to retain its proportionality, it follows that cannabis should remain in Class C.

Drug and mental health charities say the law is too blunt an instrument to deliver the public health warnings about the risks of cannabis that young people need to hear. The council is right to resist ministerial pressure. It should stick to its guns.