Just one joint could harm mental health

People who try cannabis just once can show signs of behaviour linked to schizophrenia, according to a new study.

The tests from the Institute of Psychiatry at King’s College, London, are the first to investigate the impact of exact doses of cannabis.

Researchers injected 22 healthy students and academics with Delta-9-tetrahydrocannabinol (THC), the main active ingredient of the drug. The results revealed that half the subjects showed an “acute psychotic reaction”.

The study identified a series of similarities to symptoms of schizophrenia in the responses of the individuals, including hallucinations and delusions.

The fact that the researchers found signs of psychosis in healthy people undermines previous arguments that only those with existing problems are at risk.

Dr Paul Morrison, who led the research team, concluded: “These findings confirm that THC can induce a transient acute psychological reaction in psychiatrically well individuals.”

The report, published in the Psychological Medicine journal, revealed the most common effects experienced by the subjects.

These included “people seem to be dropping hints about you or saying things with a double meaning” and “you hear your own thoughts being echoed back to you”.

They found that after the THC injections, the subjects showed “marked deficits in working memory and executive functioning and a trend towards impaired episodic memory”. All three are associated with schizophrenia.

Mary Brett, vice president of Europe Against Drugs, said: “This shows that anyone who is healthy can become psychotic by smoking cannabis. They don’t already have to have a mental illness. Healthy people can become psychotic.”

A Home Office spokesman said: “We have always said that cannabis is a harmful drug.”

But police chiefs, doctors and campaigners blame the Government for a surge in cannabis use after they weakened the law on the drug in 2004 by downgrading it to class C.

In April, a report revealed that the number of cannabis addicts receiving NHS treatment doubled in the three years after the law was relaxed.

The drug was restored to the stricter ‘B’ category of illegal drugs last year.

Almost half of 15 and 16-year-olds admit to using cannabis, according to a United Nations report, making UK teenagers the worst in Europe for cannabis use.

Last month it was revealed that a record number of young people were treated for drug or alcohol problems in England last year.

The figures, obtained from the National Treatment Agency (NTA) by the BBC showed that numbers treated with an ACCE (alcohol plus cocaine, cannabis and ecstasy) problem increased from 21,744 in 2005/06 to 31,401 in 2007/08, a rise of 44 per cent.

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