Stronger Form Of Drug Can Be Trigger For Mental illness

Although political attitudes to cannabis use have softened over the past decade, more and more evidence has emerged linking the drug to serious mental illnesses.

Many psychiatrists now believe abuse of cannabis increases susceptibility to schizophrenia, particularly in the young, while it is feared that the increasing strength of cannabis on sale in Britain could be making the problem worse.

Cannabis is thought to heighten problems with psychosis because it increases the release into the brain of a chemical called dopamine, which causes the hallucinations experienced by those suffering from schizophrenia.

One study of 50,000 conscripts into the Swedish Army found that those who smoked cannabis as teenagers were six times more likely to be diagnosed with schizophrenia than those who did not take the drug.

Robin Murray, professor of psychiatry at London’s Institute of Psychiatry, was one of the first to investigate the effects of cannabis on mental health after realising that many patients who suffered relapses also smoked the drug.

He has said: “There are now seven studies showing that if you are a heavy cannabis user in your adolescence, you increase your risk two- to threefold of going psychotic later on.”

It is believed that a particular type of gene makes some people much more likely to develop schizophrenia if they abuse cannabis while young.

Prof Murray said: “A vulnerable minority, about 25 per cent of the population, is prone to psychotic reactions if they take regular cannabis.”

Research has also shown that the incidence of schizophrenia doubled in South London between 1964 and 1999.

Prof Murray said: “Our evidence is that drug abuse contributes to that.”

In December last year the children’s mental health charity YoungMinds carried out a survey which found half of respondents who smoked cannabis – most before they were 18 – had suffered paranoia, vomiting and blackouts.

Barbara Herts, chief executive of YoungMinds, said: “We know that if young people use cannabis regularly or heavily they are at least twice as likely to develop a psychosis by young adulthood than those who don’t smoke.”

Some reports have claimed that modern cannabis, sometimes known as “skunk” because of its smell, is as much as 20 times stronger than strains of the drug available in the 1970s because of the advanced indoor cultivation techniques of British cannabis growers.

Last year police in Nottingham found cannabis plants with a Tetrahydrocannabinol (THC) content of 29 per cent, much higher than the average of 6-8 per cent content.

Marjorie Wallace, chief executive of the mental health charity Sane, added: “Cannabis, particularly in the more potent form of skunk, can increase a young person’s chances of developing schizophrenia or a similar illness by four times. The only way to prevent the risk is to give out a clear message that cannabis is still illegal.”

Gulf War veteran David Bradley, who last month admitted shooting dead four members of his family, was a daily smoker of cannabis and this is feared to have made worse his many mental health problems.

Toby Hedworth QC said: “He may have been suffering from all three [post-traumatic stress disorder, a psychotic disorder and schizophrenia] and his use of cannabis may have compounded them.”