Browsing by Author "Zellers, Stephanie"

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    Adolescent Behavioral Disinhibition And Its Relationship To Marijuana Use Development
    (2019-03) Zellers, Stephanie
    Behavioral disinhibition is a highly heritable risk factor for drug use, yet how it relates to marijuana use development is under-studied. We addressed this using independent twin samples from Colorado (N=2608) and Minnesota (N=3630), assessed from adolescence to early adulthood. We fit a biometric latent growth model of marijuana use using data from up to four waves of assessment between ages 14-24, to examine change in marijuana use and its relationship with a factor model of behavioral disinhibition. The factor structure of behavioral disinhibition, as well as its association with early marijuana use (r~.8) and increase in use (r~.3), was similar in both states. Early use was moderately heritable in both states. Increase in use was highly heritable in Minnesota (h2 =.81) but not Colorado (h2 =.14), and shared environmental effects were larger in Colorado (c2=.53) than Minnesota (c2=0). State differences in variance components could reflect state differences in culture or legal landscape. We found significant genetic correlations between disinhibition and early use in both states, as well as between disinhibition and increase in use in Minnesota (rg=.37). Lastly, exploratory analyses in Minnesota indicate that marijuana use decreases across the late 20s. This decline is strongly heritable (h2=.79) and moderately, negatively correlated with adolescent disinhibition (r=-.54). We conclude that adolescent behavioral disinhibition is positively related to early marijuana use and increase in use and negatively related to decrease in use in adulthood. This study broadens our understanding of adolescent risk and later marijuana use.
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    Impacts of Recreational Cannabis Legalization: Substance Use Development, Pre-Existing Vulnerability, and Psychosocial Outcomes
    (2022-05) Zellers, Stephanie
    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.