As public support for the decriminalisation of cannabis grows, Linsey Wynton speaks to one mother who says the drug can ruin lives.

Matthew Lancaster was a bright young man with a promising future as a computer technician ahead of him.

But by the time he was 25, his mother Lynda Lancaster barely recognised him after he became so addicted to cannabis he turned into a schizophrenic who suffered psychotic tendencies and hallucinations.

Mrs Lancaster, who now lives with her 31-year-old son in Albion Street, in Portslade, recalls Matthew telling her that he thought the television was talking to him, that the IRA and some Columbian drug barons were after him, and that she was trying to poison him.

She has memories of him losing his job, going to prison and spending his days either in bed or walking around glued to his personal stereo. She also remembers bumping into him in the supermarket where he swore at her and another shopper told her her son must be sick.

Worst of all, she cannot forget trying to wake Matthew up from a trance that he would not come out of.

Mrs Lancaster said: "Matthew's life has been ruined because of cannabis. His personality is completely different from what it was. I have been assured by doctors and psychiatrists that his condition is down to him overdosing on cannabis."

After a Mori poll showing 58 per cent of the British public believe that cannabis for personal use should be decriminalised, Mrs Lancaster felt compelled to warn them just how damaging the drug can be.

Matthew, who has agreed that his mother tells his story, smoked about one ounce of cannabis, about £90 worth, a week for about ten years from the time he was 18.

Because his parents were divorced and he was not living with her, Mrs Lancaster did not realise how serious his condition was until 1994 when he moved back in.

She said: "I would see him once or twice a week when he lived with his Dad and I remember he would giggle and talk almost in riddle.

"I didn't understand why and I even went to my own doctor to see if there was something wrong with me.

"I suppose I realised he was taking cannabis. But I had the idea in my mind that, because so many people take cannabis, it was not harmful.

"It seemed almost accepted and I just did not know what the side-effects were. I suppose I thought it was better that Matthew was taking cannabis than getting into any sort of trouble."

Nine years ago, Matthew ended up in prison for two months after being charged with affray on New Year's Eve when he was "out of it" on cannabis.

Eight years ago, he lost his job as a computer hardware technician at Ewbank Preece in Hove because he could not get up in the mornings.

By the time, he went to live with his mother he was out a lot at night and during the day he would be in bed.

He had to be sectioned and placed in hospitals for the mentally ill three times.

The last time he was sectioned was in August 1998 after Mrs Lancaster found him unconscious and took him to casualty.

Matthew was later referred to the Mill View Hospital, in Nevill Avenue, Hove, which deals with mentally ill patients.

It was there that Mrs Lancaster discovered that his cannabis habit was the root of her son's problems.

Since he came out of Mill View in November 1998, Matthew has been free of cannabis.

He now receives an injection of anti-psychotic drugs once a fortnight, which keeps him stable and he makes regular visits to the hospital.

Mrs Lancaster said: "I feel incensed that there is not enough being said about the effects of cannabis. I did not realise what a terrible effect cannabis could have.

"I am not saying that everyone will be affected in the same way, but some people like Matthew have a dreadful reaction to it.

"It is similar to the way that some smokers will get lung cancer and some people who drink will become alcoholics.

"If cigarettes and alcohol were new now they would be illegal so I totally disagree with all the public who are calling for cannabis to be decriminalised. I believe there should be more information about the very damaging effects it can have on people like Matthew.

"I just want other parents to know that they should really watch what their children are doing. People whose parents don't know what they are up to can end up on the streets.

"Sometimes I used to wish that Matthew was anywhere else but with me, but I have decided to see it through with him.

"I would not want anyone else to have to go through the heart ache that I have been through."

Consultant psychiatrist Dr Michael Rosenberg, medical director of South Downs Health NHS Trust, said: "As a psychiatrist I see people who are vulnerable to the effects of drugs and alcohol.

"The ones we see who have been affected by the use of cannabis have been affected in the following possible ways: acute parapsychosis, mimicking the effects of schizophrenia and behaving in unusual and abnormal ways.

"Cannabis can be a precipitant to the first episodes of schizophrenia in people who have a genetic predisposition to it. It can also trigger manic depressive illness.

"If somebody who suffers from mental illness brought on by the use of cannabis stopped taking cannabis they can get better but in some cases if they returned to taking cannabis their mental illness can return."

"You don't necessarily need to take cannabis on a daily basis and in strong doses to accelerate mental illness, but many of the people I see use cannabis on a daily basis.

"Some less serious mental health problems that cannabis brings on can be anxiety, depression, mild degrees of paranoia, irritability, poor concentration and lethargy.

"Many people who become mentally ill through using cannabis don't see a psychiatrist, only ten per cent of mentally ill patients actually see psychiatrists.

"Cannabis can be extremely dangerous and it's important that people know as much of the facts about it as possible.

"There is evidence that it can be addictive and it is certainly habit forming."

l A third of Britain's top bosses have tried cannabis, according to a survey in Accountancy Age magazine today.

Out of 250 financial directors, 33 per cent said they had tried cannabis and 61 per cent said they had not. The remaining six per cent declined to answer.