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Early Marijuana Use Leads to Later Brain Problems

Adults Who Started Smoking Marijuana Before Age 16 Performed Worse on Tests Than People Who Started Smoking Later

Early Marijuana Use: Perspective

The new research adds to previous studies finding other harmful brain effects, says Frances Jensen, MD, a professor of neurology at Harvard Medical School who moderated the news conference detailing Gruber's findings.

She speculates that the marijuana exposure ''is somehow modifying the way that part of the brain [the prefrontal cortex, involved in executive function tasks] is developing," she tells WebMD. "That area is one of the last parts of the brain to develop fully, she says, so the teen brain is especially vulnerable.

''Currently, it looks irreversible," she says of the damage incurred by early-onset smoking of marijuana.

This study was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.


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