NORTH-WEST health experts are convinced there is a link between cannabis and psychiatric illness.

They say there is mounting evidence that the drug can worsen or even bring on conditions such as schizophrenia.

British, Dutch, Swedish and New Zealand-based projects have all concluded there is a definite association between the drug and mental illness.

No researcher has ever said that cannabis is the root cause of a long-term psychotic condition, but the general consensus is that people with a family history of psychiatric problems should avoid it.

Bolton, Salford and Trafford Mental Health Trust medical director psychiatrist Dr Steve Colgan said: "There should be specific warnings for people vulnerable to psychosis, anxiety or depression. There's no doubt that there has been an increase in patients presenting with major psychotic disturbances and this has been related to drugs and alcohol. It's difficult to attribute it to one particular drug but cannabis is certainly the most commonly available.

"In an inner city area like this when you get young men coming in with schizophrenia, cannabis is frequently a feature and we counsel them about the dangers."

He said what was needed was a major study looking at people at various stages in their lives to see whether they smoked cannabis to ease their mental illness or if the drug had helped bring their problems on.

Until now, the measure of how pre-disposed someone was to psychosis involved looking for history of the condition in their immediate family.

Psychosis

But a British study to be published in the journal Biological Psychiatry claims to have located a genetic profile for those particularly at risk after smoking the drug.

The researchers conclude that as many as one in four people possessed a particular gene which made them more than 10 times as likely to develop psychosis following cannabis use.

Mark Holland is a consultant nurse for Manchester Mental Health and Social Care Trust.

He specialises in treating people with mental health and drug problems - a condition medics call dual diagnosis. He is interviewing drug users in the area who suffer from conditions from depression to schizophrenia.

He says in the Manchester area they have seen a marked increase in cannabis use and dual diagnosis over the last eight to 10 years.

He said: "Some people with schizophrenia smoke a joint because it makes them feel better in the short-term but we try and encourage them to stop because the evidence points to it making their condition worse.

"There's not enough evidence to prove that cannabis is a trigger, but there's enough to say that if you are pre-disposed to it then it can play a part in bringing on psychosis."

Mental health campaigners say the number of people who use drugs and have mental health problems has soared by 60 per cent in the last five years. Charity Rethink has called for swift action by the government.

North west regional manager Grainne Currie said downgrading the drug from Class B to Class C had caused confusion among younger users particularly.

"It seems young people are thinking; `if the police aren't going to arrest me then it must be ok, so why worry about it'."

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