Pot smoking changes teens' brains, study shows

By Elizabeth Lopatto
Bloomberg News Service
11/16/2010

Smoking marijuana regularly before the age of 16 causes changes in the brain that can impair a young person's ability to focus, learn from mistakes and think abstractly, according to a Harvard study.

On brain scans, the youngest pot smokers showed activation in regions of the brain that was not seen in those who started smoking after age 16, suggesting early exposure to marijuana causes neural changes, researchers at Harvard-affiliated McLean Hospital found. Early and habitual users performed more poorly on tests of cognitive functions, including mental flexibility.

Research on how marijuana changes a developing brain is important because marijuana is the most frequently used illegal drug in the U.S., said study author Staci Gruber, director of the cognitive and clinical neuroimaging core at McLean Hospital in Belmont, Mass. Almost 16 percent of eighth-graders have tried marijuana, and that number rises to 42 percent by 12th grade, a 2009 study from the National Institute on Drug Abuse found. the rest