Previous research has neglected to examine the influence of the age of initiating marijuana use in the context of current or recent levels of use. It has been hypothesized that youth who initiate use at an earlier age are likely to use more heavily by late high school and young adulthood. This study examined the influence of age of marijuana initiation on physical and mental health, as well as on two drug-related outcomes at age 18, experiencing marijuana-use related consequences and using illicit drugs other than marijuana. Data were obtained from adolescents who participated in the original field trial for Project ALERT, a drug prevention program for middle school students. Baseline survey data were collected in 1984 at grade 7 and follow-up surveys were conducted at grades 8, 9, 10, and 12 (N = 2,079). After controlling for demographic, social, and behavioral factors, findings indicate that age of initiation predicts subsequent substance-use and health-related outcomes primarily because it influences frequency of marijuana use in late adolescence. References