All participants received urine toxicology to confirm self-report and parent report of adolescent's abstinence from marijuana and other drugs, and Breathalyzers (Intoximeter, St. Louis, MO) to confirm abstinence from alcohol. BG+MJ teens were abstinent from marijuana at least 23 days (range 23−61) on the day of brain imaging. Histories of marijuana use were reported by six BG (no more than 9 episodes) and three CON (no more than 5 episodes) participants, with 30 to 1076 days since last use. Abstinence from alcohol was an average of 26 days (range 3−45 days) for BG+MJ teens, 30 days (range 13−52 days) for BG teens, and ranged from 90 to 998 days for CON, who had an average of 4 lifetime drinking episodes. Total lifetime drinking episodes in BG and BG+MJ groups ranged from 12 to 405 (see Table 1).
