Seventy-two adolescents ranging in age from 16 through 19 years participated; 36 were heavy MJ+ALC users (180-1844 lifetime occurrences of marijuana use and 25-736 lifetime alcoholic drinks), and 36 were demographically similar non-using controls (see Table 1). Participants were recruited from local high schools with comparable numbers of each group recruited from each participating school as part of an ongoing adolescent brain imaging project (e.g., Tapert et al., 2007). Participants and their parents/legal guardians were screened with separate, private interviews to ascertain eligibility. Exclusionary criteria were: DSM-IV Axis I disorder other than alcohol or marijuana use disorder; nicotine dependence (Fagerstrom Test for Nicotine Dependence (FTND) score ≥ 3), use of psychoactive medications; history of neurological disorder, head trauma with loss of consciousness >2 minutes, learning disability, chronic health problem, or complicated/premature birth (<33 weeks gestation); parental history of bipolar I or psychotic disorder; any evidence of maternal drinking (>7 drinks in a week or >4 drinks in a day) or illicit drug use during pregnancy; left handedness; MRI contraindications; and clinically abnormal brain anatomy. Participants abstained from substance use for
