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One of the key conclusions of the research is that people who start smoking cannabis as <br />adolescents are at the greatest risk of later developing mental health problems. Another <br />team calculates that eliminating cannabis use in the UK population could reduce cases of <br />schizophrenia by l 3 per cent. Until now, say Rey and Tennant, there was "a dearth of <br />reliable evidence" to support the idea that cannabis use could cause schizoplu-enia or <br />depression. That lack of good evidence "has handicapped the development of rational <br />public health policies," according to one of the research groups, led by George Patton at <br />the Murdoch Children's Research Institute in Melbourne, Australia. The works also <br />highlights potential risks associated with using cannabis as a medicine to ease the <br />symptoms of muscular sclerosis, for example. Patton's team followed over 1600 <br />Australian school pupils aged l 4 to 15 for seven years. Daily cannabis use was associated <br />with a rve-fold increased. risk of depression at the age of 20. Weekly use was linked to a <br />two-fold increase. The regular users wexe no more likely to have suffered from <br />depression or anxiety at the start of the study. The reason for the link is unclear. Social <br />consequences of frequent cannabis use include educational failure and unemployment, <br />which could increase the risk of depression. "However, because the risk seems confined <br />largely to daily users, the question about a direct pharmacological effect remains," says <br />Patton. In separate research, a team led. by Stanley Zammit at the University of Cardiff, <br />UK, evaluated data. on over 50,000 men who had been Swedish military conscripts in <br />1.969 and1970. This group represents 97 per cent of men aged 18 to 20 in the population <br />at that time. The new analysis revealed adore-dependant relationship between the <br />frequency of cannabis use aid schizophrenia. This held true in men with no psychotic <br />symptoms before they started using cannabis, suggesting they were not self-medicating. <br />Finally, researchers led by Terrie Moffitt at King's College London, UK, analyzed <br />comprehensive data on over 1.000 people born in Dunedin, New Zealand in 1972 and <br />1973. They found that people who used cannabis by age 15 were four tinier as likely to <br />have a diagnosis of schizophreniform disorder (a milder version of schizophrenia} at age <br />26 than non-users. But when the number ofpsychotic symptoms at age 11 was controlled <br />for, this increased risk dropped to become non-significant. Tlus suggests that people <br />already at greater risk of later developing mental. health. problems are also more likely to <br />smoke cannabis. The total number of high. quality studies on cannabis use and mental <br />health disorders remains small, stress Rey and Tennant. And it is still. not clear whether <br />cannabis can cause these conditions in people not predisposed by genetic factors, for <br />example, to develop them. "The overall weight of evidence is that occasional use of <br />cannabis has few harmful. effects overall," Zammit's team writes. "Nevertheless, our <br />results indicate a potentially serious risk to the mental health of people who use cannabis. <br />Such risks need to be considered in the current move to liberalise and possibty legalise <br />the use of catuiabis in the UK and other countries." <br />Journal references: British Medical Journal (vo1325, p1195, p1199, p1212, p1 l83) <br />Source: http://www.newscientist.com/article/dn3098-cannabis-link-to-mental-illness-strengthened.html <br />1.8 <br />75A-92 <br />