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  1. #1
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    New evidence of marijuana's damaging effect on brain

    New findings back evidence of marijuana's damaging effect on brain
    Associated Press - April 30, 2007

    LONDON - New findings on marijuana's damaging effect on the brain show the drug triggers temporary psychotic symptoms in some people, including hallucinations and paranoid delusions, doctors say.

    British doctors took brain scans of 15 healthy volunteers given small doses of two of the active ingredients of cannabis, as well as a placebo.

    One compound, cannabidiol, or CBD, made people more relaxed. But even small doses of another component, tetrahydrocannabinol, or THC, produced temporary psychotic symptoms in people, including hallucinations and paranoid delusions, doctors said.

    The results, to be presented at an international mental health conference in London on Tuesday and Wednesday, provides physical evidence of the drug's damaging influence on the human brain.

    "We've long suspected that cannabis is linked to psychoses, but we have never before had scans to show how the mechanism works," said Dr. Philip McGuire, a professor of psychiatry at King's College, London.

    In analyzing MRI scans of the study's subjects, McGuire and his colleagues found that THC interfered with activity in the inferior frontal cortex, a region of the brain associated with paranoia.

    "THC is switching off that regulator," McGuire said, effectively unleashing the paranoia usually kept under control by the frontal cortex.

    In another study being presented at the conference, a two-day gathering of mental health experts discussing the connections between cannabis and mental health, scientists found that marijuana worsens psychotic symptoms of schizophrenics.

    Doctors at Yale University in the U.S. tested the impact of THC on 150 healthy volunteers and 13 people with stable schizophrenia. Nearly half of the healthy subjects experienced psychotic symptoms when given the drug.

    While the doctors expected to see marijuana improve the conditions of their schizophrenic subjects - since their patients reported that the drug calmed them - they found that the reverse was true.

    "I was surprised by the results," said Dr. Deepak Cyril D'Souza, an associate professor of psychiatry at Yale University's School of Medicine. "In practice, we found that cannabis is very bad for people with schizophrenia," he said.

    While D'Souza had intended to study marijuana's impact on schizophrenics in more patients, the study was stopped prematurely because the impact was so pronounced that it would have been unethical to test it on more people with schizophrenia.

    "One of the great puzzles is why people with schizophrenia keep taking the stuff when it makes the paranoia worse," said Dr. Robin Murray, a professor of psychiatry at King's College.

    Experts theorized that schizophrenics may mistakenly judge the drug's pleasurable effects to outweigh any negatives.

    Understanding how marijuana affects the brain may ultimately lead experts to a better understanding of mental health in general.

    "We don't know the basis of paranoia or anxiety," said McGuire.

    "It is possible that we could use cannabis in controlled studies to understand psychoses better," he said. McGuire theorized that could one day lead to specific drugs targeting the responsible regions of the brain.

  2. #2
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    Scans show how cannabis affects brain

    Scans show how cannabis affects brain
    April 30, 2007

    Compound may trigger psychosis in some heavy users, scientists say

    LONDON - Brain scans showing how cannabis affects brain function may help explain why heavy consumption of the drug triggers psychosis and schizophrenia in a small number of people, scientists said on Monday.

    Psychiatrists are increasingly concerned about the mental health impact of smoking large amounts of modern super-strength marijuana, or skunk, particularly among young people.

    Until now, the mechanism by which cannabis works on the brain has been a mystery but modern scanning techniques mean experts can now detect its impact on brain activity.

    Professor Philip McGuire and Zerrin Atakan of London?s Institute of Psychiatry said their work using magnetic resonance imaging, or MRI, showed patients given the active cannabis compound tetrahydrocannabinol (THC) had reduced function in the inferior frontal cortex brain region.

    This area is associated with controlling inappropriate emotional and behavioral responses to situations.

    ?What THC seems to be doing is switching off that part of the brain, and that was associated with how paranoid people became,? McGuire told reporters.

    Their research will be presented at a two-day International Cannabis and Mental Health Conference at the Institute of Psychiatry this week.

    Similar findings from other teams also highlight the link between THC dose and the risk of schizophrenia-like symptoms, conference organizer Professor Robin Murray said.

    ?It?s no longer a contentious issue. The expert community, by and large, accepts that cannabis contributes to the onset of psychotic symptoms in general and the severe form of psychosis, schizophrenia,? he said.

    Double-strength joints
    One reason for the growing problem is thought to be the increasing strength of modern strains of cannabis, which are cultivated to produce the maximum amount of THC.

    In recent years, the average THC content of marijuana sold in Britain has doubled to 12 percent from around 6 percent, while in the Netherlands it is about 18 percent, Murray said.

    Most users of cannabis still do not have a problem with the drug but a minority, possibly because of genetic factors, are vulnerable to long-term damage from modern skunk -- which Murray says is to old-fashioned dope what whisky is to lager.

    The rise in THC content is linked with a decline in another active ingredient called cannabidiol (CBD), since the two products compete biochemically inside the cannabis plant.

    CBD, which reduces anxiety but does not produce the euphoric high of THC, may help offset some of the paranoid feelings.

    Markus Leweke of Cologne University said a clinical trial involving 42 patients showed CBD was as effective as the established medicine amisulpride, sold as Solian by Sanofi-Aventis, in treating patients with psychosis.

    ?It seems there are good guys and bad guys within cannabis,? Leweke said.

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