Adolescent Brain Particularly Susceptible to Decline in IQ from Marijuana Use

April 16, 2013 · Posted in Risk Factors 

Teen smoking marijuanaA decades-long study in New Zealand suggests that people who use marijuana persistently during adolescence lose 8 IQ points by adulthood compared to their peers who never use marijuana. Quitting or reducing cannabis use after adolescence did not restore the intellectual abilities in those who used it persistently in their youth. This is the first study of its kind that controlled for differences in functioning that existed before adolescence.

Participants took part in neuropsychological testing at the age of 13, prior to any cannabis use, and then were periodically interviewed about their use of the drug (at the ages of 18, 21, 26, 32, and 38). At age 38 they underwent IQ testing again.

Although persistent cannabis users tended to have fewer years of education, the lack of education was not responsible for the difference in adult IQ.

Those participants who only began using cannabis persistently in adulthood did not see a decline in IQ, suggesting that the adolescent brain is particularly susceptible to damage from cannabis use.

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