Heavy cannabis use can cause lasting cognitive problems in young

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Persistent cannabis use is associated with ‘neuropsychological decline’ among those whose use began in adolescence, says a new study. 

The findings are ‘suggestive of a neurotoxic effect of cannabis on the adolescent brain’ and highlight the importance of ‘prevention and policy efforts targeting adolescents’, concludes Persistent cannabis users show neuropsychological decline from childhood to midlife.

Researchers followed more than 1,000 people in Dunedin, New Zealand, from birth until the age of 38, with participants undergoing memory, intelligence, problem-solving and other neuro­psychological testing at age 13, before cannabis use had begun, and again at 38, ‘after a pattern of persistent cannabis use had developed’.

The IQ of those who had been regular cannabis users in their youth was found to have dropped by an average of eight points, a finding not replicated in those whose use began after the age of 18. The study also found that stopping use of the drug ‘did not fully restore neuropsychological functioning among adolescent-onset cannabis users’. 

Study published in the Proceedings of the National Academy of Sciences of the United States of America www.pnas.org