‘Adolescent-onset cannabis users showed significant I.Q. declines, and more persistent use was associated with greater declines,’ said the lead author, Madeline H. Meier, a postdoctoral researcher at Duke University.

The study participants who used marijuana heavily from high school through age 38 scored 8 points lower on an I.Q. test than they had when originally tested, as 13-year-olds. I.Q. scores are usually very stable, and those who did not use marijuana or started as adults showed no real change, averaging about 100.

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Bad news for everyone I know?

http://well.blogs.nytimes.com/2012/08/27/early-marijuana-use-linked-to-to-i-q-loss/?ref=health