David Baxter PhD
Late Founder
Mental health warning for cannabis users
December 2, 2004
By Nic Fleming, The Telegraph
Young people with a family history of mental illness were warned yesterday that smoking cannabis substantially increases their chances of developing psychiatric problems.
Those who are genetically vulnerable to psychosis double the risks of hallucinations, paranoia and serious conditions such as schizophrenia by using the drug.
The study, to be presented at an Institute of Psychiatry conference in London today, confirmed previous findings that for an average person taking cannabis once or twice a week the risk of suffering psychotic symptoms roughly doubles in later life.
Prof Jim van Os, a psychiatrist at Maastricht University in the Netherlands, said: "There have been a number of studies that have shown that cannabis use roughly doubles the risk of psychiatric illness such as schizophrenia among young people.
"There have been suggestions that cannabis can interact with pre-existing, possibly genetic, vulnerability to psychotic symptoms.
"Our results show that in the group with no pre-existing vulnerability to psychosis, cannabis use increased the chances of the onset of psychosis by a small amount.
"However for those who had shown evidence of being predisposed, the increased risks of developing problems were four times greater than for those not considered vulnerable."
The new research, published by bmj.com, opens the way to the possibility of a genetic test that would tell people if they were at greater risk from cannabis use and of better targeting of public health advice.
Prof van Os's team interviewed 2,437 Germans aged 14 to 24 to assess their drug use and vulnerability to psychosis by asking questions designed to reveal traits such as paranoia, suspicion and delusions.
Ten per cent were viewed as potentially vulnerable to psychotic symptoms, ranging from hallucinations and delusions to serious conditions requiring hospital treatment.
The group was assessed four years later. Of those found not to be predisposed to psychosis, 15 per cent of those who did not use the drug and 21 per cent of those who did experienced some symptoms.
Among the volunteers identified as genetically vulnerable to psychosis, 51 per cent of cannabis users had symptoms compared with 26 per cent of those who did not use the drug.
Across the whole group, cannabis use, defined as at least five times, was found to increase the risk of psychosis by two thirds. Using the drug on average between once and twice a week increased the chances of symptoms by 95 per cent.
Prof van Os said: "The public health message is that if people have a family history of mental instability then they should know there are high risks associated with cannabis use."
Other researchers said the risks of mental illness were also increased by the trend in recent years of increasing amounts of THC "the active ingredient in cannabis" in the drug, and young people starting to use it earlier.
A report released last week showed that schoolchildren in England were using more cannabis than in any other country in Europe. The European Monitoring Centre for Drugs and Drug Addiction disclosed that among 15-year-olds, 42 per cent of boys and 38 per cent of girls had tried cannabis, compared with less than 10 per cent in Greece, Malta, Sweden and Norway. More than one in 10 15-year-olds in England reported heavy cannabis use "defined as 40 or more occasions a year" compared with the next biggest groups of seven per cent in Spain and Belgium.
Marjorie Wallace, the chief executive of the mental health charity Sane, said: "The evidence is mounting that cannabis can be the trigger to lifelong mental illness. We need to make these risks known, clamp down on drug dealing in such places as playgrounds and hospital wards, and change perceptions of cannabis from being a recreational relaxant to a dangerous substance for those who are vulnerable."
December 2, 2004
By Nic Fleming, The Telegraph
Young people with a family history of mental illness were warned yesterday that smoking cannabis substantially increases their chances of developing psychiatric problems.
Those who are genetically vulnerable to psychosis double the risks of hallucinations, paranoia and serious conditions such as schizophrenia by using the drug.
The study, to be presented at an Institute of Psychiatry conference in London today, confirmed previous findings that for an average person taking cannabis once or twice a week the risk of suffering psychotic symptoms roughly doubles in later life.
Prof Jim van Os, a psychiatrist at Maastricht University in the Netherlands, said: "There have been a number of studies that have shown that cannabis use roughly doubles the risk of psychiatric illness such as schizophrenia among young people.
"There have been suggestions that cannabis can interact with pre-existing, possibly genetic, vulnerability to psychotic symptoms.
"Our results show that in the group with no pre-existing vulnerability to psychosis, cannabis use increased the chances of the onset of psychosis by a small amount.
"However for those who had shown evidence of being predisposed, the increased risks of developing problems were four times greater than for those not considered vulnerable."
The new research, published by bmj.com, opens the way to the possibility of a genetic test that would tell people if they were at greater risk from cannabis use and of better targeting of public health advice.
Prof van Os's team interviewed 2,437 Germans aged 14 to 24 to assess their drug use and vulnerability to psychosis by asking questions designed to reveal traits such as paranoia, suspicion and delusions.
Ten per cent were viewed as potentially vulnerable to psychotic symptoms, ranging from hallucinations and delusions to serious conditions requiring hospital treatment.
The group was assessed four years later. Of those found not to be predisposed to psychosis, 15 per cent of those who did not use the drug and 21 per cent of those who did experienced some symptoms.
Among the volunteers identified as genetically vulnerable to psychosis, 51 per cent of cannabis users had symptoms compared with 26 per cent of those who did not use the drug.
Across the whole group, cannabis use, defined as at least five times, was found to increase the risk of psychosis by two thirds. Using the drug on average between once and twice a week increased the chances of symptoms by 95 per cent.
Prof van Os said: "The public health message is that if people have a family history of mental instability then they should know there are high risks associated with cannabis use."
Other researchers said the risks of mental illness were also increased by the trend in recent years of increasing amounts of THC "the active ingredient in cannabis" in the drug, and young people starting to use it earlier.
A report released last week showed that schoolchildren in England were using more cannabis than in any other country in Europe. The European Monitoring Centre for Drugs and Drug Addiction disclosed that among 15-year-olds, 42 per cent of boys and 38 per cent of girls had tried cannabis, compared with less than 10 per cent in Greece, Malta, Sweden and Norway. More than one in 10 15-year-olds in England reported heavy cannabis use "defined as 40 or more occasions a year" compared with the next biggest groups of seven per cent in Spain and Belgium.
Marjorie Wallace, the chief executive of the mental health charity Sane, said: "The evidence is mounting that cannabis can be the trigger to lifelong mental illness. We need to make these risks known, clamp down on drug dealing in such places as playgrounds and hospital wards, and change perceptions of cannabis from being a recreational relaxant to a dangerous substance for those who are vulnerable."
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