THE number of schoolchildren using cannabis has increased more than 10 times since 1987, according to a study of 350,000 teenagers to be published this week.

The research also shows that some 7% of 12 to 13-year-old boys and 6% of girls have taken the drug.

The soaring rise in the use of cannabis by children will fuel calls for a change in the legal status of the drug after it was downgraded from class B to class C last year when David Blunkett was home secretary.

In March, Charles Clarke, Blunkett’s successor, asked the Advisory Council on the Misuse of Drugs (ACMD) to re- examine the harmfulness of the drug after a report from Maastricht University concluded that the use of cannabis “moderately increases” the risk of psychotic symptoms in young people.

The new study by the Schools Health Education Unit, entitled Young People and Illegal Drugs, shows that the proportion of 14 to 15-year-old boys reporting that they have taken cannabis increased from 2% in 1987 to 26% last year. For girls the figure rose from 2% to 27%.

In the same period, the proportion of 12 to 13-year-old boys taking the drug went up from 1% to 7%, while for girls the figure went from zero to 6%.

The increased cannabis consumption is in marked contrast to other drugs, according to the research, with large falls in the use of recreational drugs such as amphetamines and ecstasy since the mid-1990s.

David Regis, author of the survey, said the increased availability of cannabis had contributed to the rise. “Over the last 20 years there has been a huge rise in youngsters’ encounters with cannabis,” he said.

“But we have also seen improvements in awareness of the dangers of drugs such as amphetamines which is partly to do with better education about the dangers.”

Mental health campaigners have voiced growing concerns about the decision to downgrade cannabis, pointing to growing evidence that suggests it is more damaging to mental health than previously thought.

A study published earlier this year by King’s College London found that one in four people carried genes that increased vulnerability to psychotic illnesses if they smoked cannabis as a teenager. It identified a genetic profile that makes cannabis five times more likely to trigger schizophrenia.

Last month researchers at Aberdeen University found the drug could increase bone loss, leading to osteoporosis.

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