Study: Heavy marijuana use lowers IQ, alters shape of brains

November 12, 2014 7:18 PM

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The research in this week’s Proceedings of the National Academy of Sciences used magnetic resonance imaging to measure people who used marijuana three times a day on average. The users had smaller amounts of gray matter and increased connectivity in the orbitofrontal cortex — a section associated with decision-making and response to rewards — and the changes were more pronounced in people who had started using earlier.

The study adds to a growing collection of evidence that marijuana alters the young brain, just as more parts of the U.S. are decriminalizing the drug and more young people are using it. Current research indicates the brain doesn’t reach maturity until age 25 or 30, and people should hold off heavy p...

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