THE number of children treated for mental disorders caused by smoking cannabis has quadrupled since the government downgraded the legal status of the drug, according to a leading drug charity.

Since April last year, three months after police stopped arresting anyone found in possession of small amounts of the drug, the overall number of users treated for such conditions rose 42%, according to data from Addaction.

But it is the figure for children that will cause the greatest alarm. Addaction treated 1,575 cannabis users for psychotic problems between April 2004 and April 2005, of whom 181 were aged 15 or below — a rise of 136 on the previous year.

Many experts blame the relaxation of the law and the wider use of skunk, a high-strength variant of cannabis.

“A minority of people who take it repeatedly and over a long period, particularly people who take it as adolescents, will suffer psychotic episodes. They may ultimately suffer schizophrenia,” said Robin Murray, professor of psychiatry at King’s College London.

Addaction’s findings are backed up by recent government figures that reveal a 22% leap in hospital admissions attributed directly to cannabis. They show that 710 people were sent to hospital with mental illness caused by cannabis in the 12 months to April 2004, up from 580 in the two previous years.

The Advisory Council on the Misuse of Drugs is meeting next weekend to decide whether there should be a full review of the working of the cannabis law. It was set up by Charles Clarke, the home secretary, after research released earlier this year suggested cannabis may cause mental illness.

A New Zealand research project involving 1,000 people born in 1977 found that cannabis could double the risk of mental illnesses such as schizophrenia. A Dutch study by Professor Jim van Os also discovered that frequent cannabis use during adolescence increased the risk of psychotic symptoms later in life, especially among those genetically vulnerable to mental illness.

A member of the committee said this weekend, however, that the panel was unlikely to recommend any revision of the law because there was still insufficient evidence to show any increased risk. One option it is considering is upgrading skunk but leaving “ordinary” cannabis as a class C drug.

Jonathan McDonnell, project manager for the Buckinghamshire branch of Young Addaction, said that last year 250 cannabis users under 19 were referred to his unit for treatment; 85% of those were skunk users.

He said that the higher street price of skunk — £20 for an eighth of an ounce rather than £12 for normal cannabis — meant that many users were now involved in “junkie crimes” such as burglary and robbery, traditionally the preserve of hard-drug users.

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