PROJECT SUMMARY/ABSTRACT Our study will contribute to the evidence about effects of drug decriminalization policy, by assessing implementation and outcomes from Oregon’s November 2020 ballot initiative Measure 110: Drug Addiction Treatment and Recovery Act (M-110). This measure decriminalizes possession of small amounts of drugs and reduces criminal penalties for greater offenses. Possession of small amounts of drugs would no longer be a crime, but instead result in a civil penalty, with a $100 fine that can be waived by participating in a health assessment provided through M-110-established regional Addiction Recovery Centers (ARCs). This is the first such policy to be passed in the United States. The aims of this proposed administrative supplement would build on the parent study’s data and approaches to assess implementation of substance use policies and associated outcomes, and how variability in local policies is associated with different outcomes, including in rural and urban community settings and among different population groups. The first aim will provide a systematic description of trends in behavioral health system capacity following implementation of M-110 provisions, including time-varying local-level funding for behavioral health, availability of treatment services, and health assessments delivered. The second aim will assess trends in delivery of public-paid substance use dependence treatment services. The third aim will assess trends in drug- related hospitalizations and emergency department (ED) visits. Aims 2 and 3 will describe Oregon trends, assess whether there are differences in trends for different community types (e.g., urban/rural) or for different groups of individuals (e.g., by race/ethnicity, age, gender, and income), and whether variability is explained by differences in community-level behavioral health capacity. We will address these aims using quasi-experimental methods developed in our parent study, which exploit within-state and across-time variation in local policies. Public health surveillance data for the study are in-hand from the parent grant, including hospitalization and ED data and public-paid treatment (Medicaid charge) data. Findings from this study will be critical for understanding the effects of drug decriminalization policy, and potential contribution to health equity.