USA – Marijuana may hurt the developing teen brain

In childhood our brain is larger, says Krista Lisdahl, director of the brain imaging and neuropsychology lab at University of Wisconsin, Milwaukee. During the teenage years, our brain is getting rid of those connections that weren’t really used, and it prunes back. Researchers from Duke University analysed data gathered over many years from people living in New Zealand. They compared IQs in childhood through age 38 among marijuana users and nonusers. “We found that people who began using marijuana in their teenage years and continued to use marijuana for many years lost about eight IQ points from childhood to adulthood”, says study author Madeline Meier, now a professor at Arizona State University, “whereas those who never used marijuana never lost IQ points.” ]]>