A large, long-term study led by researchers from Britain and the United States found that persistent and dependent use of cannabis by teens prior to turning 18 may cause lasting damage to their memory, intelligence and attention. The study involved more than 1,000 people who were followed for over 40 years. The data came from 1,037 New Zealanders – of which 96% remained in the study which was conducted from 1972 through this year.  At the age of 38, the participants underwent a series of psychological tests to check their memory, processing speed, visual processing and reasoning.  The persistent adolescent pot smokers scored significantly poorer in almost all of the tests.  The research also found that the participants who had smoked pot persistently as teens, and continued for years beyond adolescence showed an average decline in Intelligence Quotient (IQ) test scores of 8 points between the ages of 13 and 38.  Terrie Moffitt, a psychology and neuroscience professor at King’s College Institute of Psychiatry and researcher in the study said the IQ decline was directly linked to the age when people began to smoke pot, rather than other variables such as alcohol or other drug usage, or less education.  Moffitt said that prior to turning 18, the brain is still being “organized and remodeled” to become more efficient – causing it to be more vulnerable to injury from drugs.”

“It is of course part of folk-lore among young people that some heavy users of cannabis seem to gradually lose their abilities and end up achieving much less than one would have anticipated.  This study provides one explanation as to why this might be the case,” said Robin Murray a professor of psychiatric research at King’s Institute of Psychiatry.  Murray, who was not part of this study said the findings should be taken “very seriously.”  The researchers also concluded that heavy pot use begun after 18 seems to be less harmful to the brain.  “Study subjects who didn’t take up pot until they were adults with fully-formed brains did not show similar mental declines,” Moffitt said.       ChicagoTribune.com     8/28/12

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