Cannabis danger exposed

Cannabis use is now the biggest single cause of serious mental disorders in the UK, a leading expert warned yesterday.

Up to 80 per cent of new patients at many units have a history of smoking the drug, said consultant psychiatrist Professor Robin Murray.

The stark message comes just three weeks before the Government officially downgrades cannabis to Class C, putting it on the same level as growth hormones and prescription painkillers.

Doctors fear that the change will wrongly lead young people to believe the drug is harmless and that more people will try it as they are unlikely to be prosecuted.

Professor Murray, head of psychiatry at the Institute of Psychiatry, said the vast majority of psychotic patients - those who lose contact with reality and are unable to function in their daily lives - have used cannabis.

He said the Government had a duty to warn people of the 'possible downside' after pressing ahead with plans to downgrade the drug despite widespread concern.

'There is a terrible drain on resources,' he said. 'Not only are there people suffering from psychosis who would not be in in-patient beds if they were not using cannabis, but the drug also drastically reduces recovery - people who improve go out on the street, meet their dealer, use the drug again and relapse.

'I would say this is now the number one problem facing mental health services in inner cities.

'In South London the incidence of psychosis has doubled since 1964.'

About 3.2million people in the UK use cannabis regularly and a third of all 15-year-olds have tried the drug, according to official figures.

Professor Murray, a consultant psychiatrist at the Maudsley Hospital in South London, said there were no experts in psychosis on the committee that advised the Government on cannabis classification.

He added: ' Since then, there have been at least four studies that show the use of cannabis, particularly in young people, can significantly increase the likelihood of the onset of psychosis.'

Professor Murray himself led a study last year which showed that cannabis users are seven times more at risk of developing mental illness than the population in general.

Experts believe the figures reflect the fact that cannabis typically contains ten times as much tetrahydrocannabinol (THC) - the crucial ingredient which induces the feeling of being 'high' - today as it did in the 1960s and 1970s.

THC disrupts the chemical balance in the brain. This may result in memory loss and anxiety and cause excess levels of dopamine, a symptom associated with schizophrenia.

Cannabis also causes cancer and lung disease and doctors say it could be responsible for 30,000 deaths a year in the UK.

It will be downgraded from January 29, after which those caught in possession for personal use can expect the police simply to confiscate the drug and issue a routine warning.

A Home Office spokesman said: 'The point of the reclassification is to allow police to target class A drugs like heroin and crack cocaine, which cause the most harm to families and the community.

'The view of the medical experts on the advisory council that advised on the reclassification remains unchanged.'