Teenagers who regularly smoke cannabis risk permanently damaging their intelligence, attention span and memory. Stopping or reducing cannabis use fails to fully restore the lost IQ.

Source: Teenage cannabis smoking ‘permanently damages IQ’ @ ITV News

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  • Young cannabis smokers run risk of lower IQ, report claims @ BBC News

    Excerpt: Young people who smoke cannabis for years run the risk of a significant and irreversible reduction in their IQ, research suggests. An international team found those who started using cannabis below the age of 18 – while their brains were still developing – suffered a drop in IQ. A UK expert said the research might explain why people who use the drug often seem to under-achieve.

  • Persistent cannabis users show neuropsychological decline from childhood to midlife @ Proceedings of the National Academy of Sciences of the United States of America

    Excerpt: Persistent cannabis use was associated with neuropsychological decline broadly across domains of functioning, even after controlling for years of education. Informants also reported noticing more cognitive problems for persistent cannabis users. Impairment was concentrated among adolescent-onset cannabis users, with more persistent use associated with greater decline. Further, cessation of cannabis use did not fully restore neuropsychological functioning among adolescent-onset cannabis users. Findings are suggestive of a neurotoxic effect of cannabis on the adolescent brain and highlight the importance of prevention and policy efforts targeting adolescents.