Zellers, Stephanie2024-07-242024-07-242022-05https://hdl.handle.net/11299/264379University of Minnesota Ph.D. dissertation. May 2022. Major: Psychology. Advisor: Scott Vrieze. 1 computer file (PDF); vi, 149 pages.Alcohol, tobacco, and cannabis are three of the most commonly consumed substances in the United States. The development of substance use is influenced by genes, the familial environment, and unique environmental exposures. One such exposure is legal policy surrounding the purchase and consumption of these substances, and cannabis policies in particular are changing dramatically across the United States, raising concerns about the potential for public health consequences associated with substance use. In the present work, we focus on the development of substance use in a normative community sample, as well as perturbations to substance use development and substance related outcomes as a consequence of recreational legalization using causally informative genetic longitudinal designs. Study 1 explores normative developmental trends of cannabis use in recreationally illegal environments and its relationship to development of alcohol and tobacco consumption from adolescence through mid-adulthood. Study 1 also investigates the genetic and environmental influences underlying all three substances and influences unique to each substance over time. Study 2 evaluates the causal impact of recreational legalization on cannabis frequency with a co-twin control model, as well as the changes to the magnitude genetic and environmental influences on cannabis use in a longitudinal gene-environment interaction model. Study 3 expands on this to evaluate the impact of recreational legalization on a broad range of psychiatric and psychosocial outcomes associated with cannabis use, and further examines whether vulnerable individuals are at exacerbated risk for negative outcomes due to legalization. Together, these studies use rigorous designs to expand on the existing literature and provide evidence consistent with a causal impact of cannabis legalization on cannabis use. Furthermore, our results suggest that cannabis legalization may perturb normative adult decreases in substance intake, but this is not coupled with negative psychosocial outcomes in adulthood.encausal inferencediscordant twingene-environment interactiontwin studyThesis or Dissertation