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Most research on brain changes associated with marijuana use has been done in dependent, heavy users. In this magnetic resonance imaging study, the 20 young adult marijuana users (age range, 18–25; 11 females) did not meet criteria for dependence; on average they smoked almost 4 days and 11 joints per week. The 20 control subjects, who were matched for age, sex, handedness, race, and years of education (mean, 13 years), had smoked marijuana fewer than five times in their lifetime and not at all in the past year. Marijuana users consumed nonsignificantly more alcohol per week than controls (5.0 vs. 2.6 drinks) and scored higher on a measure of alcohol abuse (P=0.05).
Analyses were adjusted for age, sex, and alcohol and cigarette use. Whole-br…