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Early Marijuana Use May Impair Brain Function06:38
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An MRI of a human brain (Reigh LeBlanc/Flickr)
An MRI of a human brain (Reigh LeBlanc/Flickr)

A study released Monday by McLean Hospital in Belmont shows that individuals who start using marijuana before the age of 16 are more impaired when it comes to so-called executive function — such as planning, flexibility and abstract thinking — than those who start smoking pot at a later age.

Lead researcher Staci Gruber also says that early onset users smoke three times as much as those who start smoking marijuana later.

"We have to be clear about getting the message out that marijuana isn't really a benign substance," Gruber said. "The earlier you begin using it, and the more you use of it, the more significant that effect."

Compared to control subjects, marijuana smokers show increased activation in the front area of the brain, a key region for inhibition, attention and error processing.  Additionally, the study found that those who started smoking earlier activated a different part of the brain than those who started smoking after the age of 16; this suggests there may be a neural change in response to marijuana use at an early age.

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This segment aired on November 15, 2010.

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