Zellers, Stephanie2020-08-252020-08-252019-03https://hdl.handle.net/11299/215046University of Minnesota M.A. thesis.March 2019. Major: Psychology. Advisors: Scott Vrieze, Matt McGue. 1 computer file (PDF); vi, 43 pages.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.enbehavioral disinhibitionexternalizingheritabilitylatent growth modelmarijuanastructural equations modelThesis or Dissertation