Dependency on marijuana damages intelligence, shows study

August 28th, 2012 - 2:51 pm ICT by IANS  

Washington, Aug 28 (IANS) Dependency on marijuana before 18 years of age may cause lasting damage to the addict’s intelligence, attention and memory, according to an international research.

A long-range study of more than 1,000 New Zealanders, individuals who started using cannabis in adolescence and used it for years afterward, showed an average decline in IQ of eight points when their age 13 and age 38 IQ tests were compared.

Quitting pot did not appear to reverse the loss either, said Madeline Meier, post-doctoral researcher at Duke University and study co-author, the journal Proceedings of the National Academy of Science reports.

The key variable in this is the age of onset for marijuana use and the brain’s development, Meier said. Study subjects who didn’t take up pot until they were adults with fully-formed brains did not show similar mental declines, according to a Duke statement.

Before 18 years of age, however, the brain is still being organised and remodelled to become more efficient, she said, and may be more vulnerable to damage from drugs.

“Marijuana is not harmless, particularly for adolescents,” said Meier, who produced this finding from the long term Dunedin Multidisciplinary Health and Development Study.

The study has followed a group of 1,037 children born in 1972-73 in Dunedin, New Zealand, from birth to age 38 and is led by Terrie Moffitt and Avshalom Caspi, psychologists who hold dual appointments at Duke and the Institute of Psychiatry at King’s College London.

At the age of 38 years, all the study participants were given a battery of psychological tests to assess memory, processing speed, reasoning and visual processing. The people who used pot persistently as teens scored significantly worse on most of the tests.

Friends and relatives routinely interviewed as part of the study were more likely to report that the persistent cannabis users had attention and memory problems such as losing focus and forgetting to do tasks.

The decline in IQ among persistent cannabis users could not be explained by alcohol or other drug use or by having less education, Moffitt said.

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