Chan G, Connor J, and Hall W, et al. - Among young Australians, population-level classes of polysubstance use between 2004 and 2016 were investigated, as were changes over the same period in these classes in terms of class prevalence and probabilities of substance use within each class and demographic and health-related correlates of polysubstance. Repeated cross-sectional nationally representative household surveys from all Australian states/territories from the National Drug Strategy Household Surveys of young adults aged 18-30 years (58% females; n = 20,350) were analyzed. The identified polysubstance use classed were minimal users (MU, ~60%), mainly tobacco, alcohol and cannabis users (TAC, ~30%) and extended range polysubstance users (POLY, ~10%). Only the first two classes showed a reduction in harmful alcohol use, while All classes displayed a decrease in smoking. Over the study period, similar factors were associated with TAC and POLY, including being male, having an English-speaking background, a high level of psychological distress, suboptimal health, and high personal income. Researchers observed a link between living in an affluent area with lowerlikelihood of being TAC, but with a higherlikelihood of being POLY.