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Study suggests marijuana changes brain structure

Heavy marijuana users had different brain shapes and lower IQs than nonsmokers in a newly published study, suggesting a danger to young people who abuse the drug.

Heavy marijuana users had different brain shapes and lower IQs than nonsmokers in a newly published study, suggesting a danger to young people who abuse the drug.

The research in the Proceedings of the National Academy of Sciences used magnetic resonance imaging to measure people who used marijuana three times a day on average. They 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 started using earlier.

The study adds to a growing collection of evidence that marijuana alters the young brain, just as more areas 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 pot use before then, said Francesca Filbey, who co-authored the study.

The data included 48 heavy marijuana users, 28 years old on average, plus 62 non-users of the same genders and ages. The research, which controlled for alcohol and tobacco use, suggested people who used often had increased connectivity in their brains - possibly compensating for the effects of drug use, Filbey said.

After about five years of drug use, the increased connectivity dropped off, which could mean the brain was no longer able to make up for the negative effects of the marijuana. The earlier someone started, the worse the result. - Bloomberg News