Birth Cohorts Analysis of Adolescent Cigarette Smoking and Subsequent Marijuana and Cocaine Use.

Objectives: To examine whether the drug behavior of adults from different birth cohorts is shaped by adolescent drug experiences and whether adult prevalence of marijuana and cocaine use depends on adolescent cigarette or alcohol use prevalence.
Methods: We analyzed 18 birth cohorts comprising 8th, 10th, and 12th graders, sampled from 1991 to 2008, from Monitoring the Future, an annual nationally representative cross-sectional survey of high school students in the United States (n = 864 443).
Results: Within cohorts, lifetime rates of 8th and 10th grade cigarette use were significantly associated with subsequent lifetime rates of marijuana and cocaine use, controlling for trends in use and social norms toward drug use. Each percent increase (or decrease) in 8th and 10th grade smoking was associated with an 8% increase (or decrease) in prevalence of later marijuana use and 14% to 23% increase (or decrease) in prevalence of later cocaine use. Relationships were consistent by gender and race/ethnicity.
Conclusions: Prevalences of smoking in 8th and 10th grade and of marijuana and cocaine use in 12th grade are associated. Public health campaigns should focus on early stages of adolescence, when drug use habits are forming.