Degenhardt L, et al. - In this investigation involving 90,027 participants from the World Mental Health Surveys, researchers sought to use cross-national data to analyze time-space variation in cohort-level drug use to evaluate its connections with onset and transitions across stages of drug use, abuse, dependence, and remission. Of these participants, at some stage in their lifetime, 1 in 4 revealed either illicit drug use or extra-medical use of prescription drugs, but with significant time-space variability in this incidence. Findings suggested an association of birth cohort substance use with drug use involvement beyond the outcomes of individual histories of alcohol and other drug use. For understanding pathways into and out of problematic drug use, this has significant implications.