Developing explanatory models for life course shifts in the burden of substance use to inform future policy and practice.

Past approaches to policy and practice for substance use have focused heavily on young people, but recent trends indicate this approach may not be where the future lies. The crises with escalating overdose mortality in several countries, particularly overdoses related to opioids, have drawn attention to life course shifts in the burdens of substance use. Overdose mortality rates for individuals in midlife have considerably outpaced those of adolescents and individuals in early adulthood. These diverging life course trends are occurring not only in the United States, but in other countries with growing overdose problems as well. The future of effective policy and practice depend upon evidence and analyses that adapt to emerging data on shifting life course trends in drug related mortality. Within this manuscript, we consider a range of theoretical possibilities on the divergence of midlife drug mortality trends from those of young people for the purpose of outlining an agenda for future research and practice. Specifically, we consider the following theoretical approaches to move research forward in this area: Changes in Medical Context hypothesis; Emergent Comorbidities hypothesis; Cohort hypothesis; Generational Forgetting hypothesis; Legal Regulation hypothesis; Strength of Life Course Bonds hypothesis; Deepening Inequality hypothesis; Measurement Reliability hypothesis. These theoretical frameworks attend specifically to the overdose crisis but extend to other aspects of substance use. Beyond setting an agenda for research by providing empirically verifiable hypotheses, this manuscript also identifies future directions in policy and practice that are attentive to life course trends.