age 24 (.85) was 98% of the initiation probability by age 36 (.87). The percentage of cannabis abstainers in both cohorts differed by only 8.2% (Cohort II: abstention rate=40.4%, Cohort III: rate=32.2%), and the percentage of tobacco abstainers differed by only 1.1% (Cohort II: abstention rate=11.5% Cohort III: rate=12.6%). Further, the median age of first tobacco use was 14 among both men and women, and the median age of first cannabis use was 18 among both men and women. By contrast, the median age at interview among abstainers from tobacco was 30 for men and 31 for women, and the median age among abstainers from cannabis was 30 for men and 31 for women. Taken together, these data suggest that most abstainers had passed through their period of risk and are likely to remain abstainers.
