People who start smoking marijuana before they turn 16 may damage their brains more than people who start later, according to a small study from McLean Hospital released yesterday. Early-onset users also smoke more marijuana and more often over the course of a week than later-onset users, the researchers found…

Staci Gruber, director of the Cognitive and Clinical Neuroimaging Core at McLean in Belmont and assistant professor of psychiatry at Harvard Medical School, led a team that tested mental focus and flexibility among 33 young marijuana users and 26 non-users recruited from Greater Boston…

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