Skunk increases psychosis risk seven-fold, says study

A stronger form of cannabis which is common on British streets is almost seven times more likely to trigger psychosis than ordinary cannabis, according to a new study.

Scientists made the discovery after studying admissions to hospital for psychotic illnesses such as schizophrenia and paranoia.

The study was carried out by the Institute of Psychiatry at King’s College London.

Dr Marta Di Forti, who led the research team, said: “Our most striking finding is that patients with a first episode of psychosis preferentially used high-potency cannabis preparations of the skunk variety.”

The research results come after Prof David Nutt’s sacking as chairman of the Government’s Advisory Council on the Misuse of Drugs (ACMD) over his controversial views on cannabis.

Mr Nutt has criticised the Government for reclassifying cannabis to Class B, a decision it made partly because of concerns about the mental health effects of the drug.

Dr Di Forti and her team collected information from 280 people attending South London and Maudsley NHS Foundation Trust who were suffering their first symptoms of psychosis.

They found the patients were twice as likely to have used cannabis for more than five years, and six times more likely to use it everyday than a control group of healthy individuals.

Among those who had used cannabis, patients with psychosis were almost seven times more likely to use skunk.

Dr Di Forti said: “Psychosis was associated with more frequent and longer use of cannabis.”

She also said: “Our study is the first to demonstrate that the risk of psychosis is much greater among people who are frequent cannabis users, especially among those using skunk, rather than occasional users of traditional hash”.

Dr Di Forti added: “Unfortunately, skunk is displacing traditional cannabis preparations in many countries, and the availability of skunk on the UK ‘street market’ has steadily increased over the past six years.

“Public education about the risks of heavy use of high potency cannabis is vital.”

Marjorie Wallace, Chief Executive of the mental health charity SANE, said: “Those of us on the front line, including psychiatrists, police and families, know that skunk cannabis can be particularly dangerous for the significant minority of people vulnerable to mental illness.

“We need to give out an uncompromising warning about the specific links between skunk and mental illness.”

The strong links between all forms of cannabis use and severe mental health problems have been widely acknowledged.

Between 1997 and 2006 cannabis-related admissions to hospitals on mental health grounds rose by 85 per cent, according to Government figures.

There are now more than 22,000 people a year, almost half under the age of 18, being treated for cannabis addiction. In 1997 the number was 1,600.

Another study lasting 27 years and involving 50,000 people showed that smoking cannabis trebles the risk of a young person developing schizophrenia.

After cannabis was downgraded to class C in 2004, judges, police, parents and mental health experts called for the move to be reversed because of the damage it causes.

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