Trajectories of polysubstance use: Are past-year internalizing and externalizing problems associated with trajectories of polysubstance use over time?

Objective: Polysubstance use among adults has been a public health concern in the U.S. and is associated with adverse consequences. This study aimed to identify the longitudinal trajectory of polysubstance use and test whether internalizing and externalizing problems predict it. Methods: Data of adults aged 18 and older (N = 15076) were extracted from the Waves 1-5 Population Assessment of Tobacco and Health Study (2013-2019). Group-Based Trajectory Modeling was performed to identify the trajectory of polysubstance use. Examined substances included use of cigarettes, e-cigarettes, excessive alcohol, cannabis, painkillers, and cocaine in past 30 days from all waves. Weighted multinomial logistic regressions were conducted to investigate the associations between internalizing and externalizing problems and the trajectory of polysubstance use, controlling for demographic variables. Results: Five trajectory groups were identified: (1) No to minimal polysubstance use risk (45.6 %); (2) Polysubstance use-low risk (10.7 %); (3) Cigarette-leading polysubstance use-high risk (23.5 %); (4) Cigarettecannabis co-leading polysubstance use-high risk (12.3 %); and (5) Cannabis-leading polysubstance use-high risk (7.8 %). Compared with Group 1, higher internalizing problems predicted the membership of Group 3 [Relative risk ratio (RRR) range: 1.07-1.17] and Group 4 (RRR range: 1.04-1.21). Compared with Group 1, higher externalizing problems predicted the membership of Group 5 (RRR range: 1.01-1.10). Conclusions: Prevention efforts should consider internalizing problems and associated trajectories of high-risk polysubstance use (e.g., cigarette-leading and cigarette-cannabis co-leading) as well as externalizing problems and associated trajectories of high-risk polysubstance use (e.g., cannabis-leading), when designing interventions to prevent polysubstance use.