Project Summary In response to the opioid epidemic, states are increasingly passing legislation to influence how opioids are prescribed. As an R15 proposal, this study involves undergraduate students’ mentored investigation of whether a particularly comprehensive opioid prescribing policy was able to increase access to guideline-concordant pain care in primary care among adult Medicaid patients. The students would make major contributions to the study of changes in prescribing practices and other aspects of pain care associated with a newly implemented Nevada law, Assembly Bill 474. This law closely aligns with some CDC guidelines for pain care in primary care, but there are also guidelines recommended by the CDC that are not explicitly mentioned in the law. This study will look at both changes in guideline-concordant practices that are mentioned by the law and changes in related guideline-concordant practices that are not. This will generate new knowledge about whether the law was associated with broader guideline dissemination. This study will further address potential differences in the effects of the law in urban areas and rural/frontier areas, where Nevada’s opioid epidemic is particularly hard-hitting. Studying the Medicaid population brings focused attention to a population that is at higher risk for fatal opioid overdoses than other populations. It also increases the policy relevance of this problem as state Medicaid programs often cover mediation-assisted treatment therapies used to treat patients with opioid use disorders. Nevada is a well-suited laboratory for this study due to AB474 alignment with many of the 2016 Centers for Disease Control and Prevention recommendations for pain care in primary care. This work innovates in its use of clinical guidelines as outcomes, which increases the clinical relevance and interpretability of the findings. The results will have policy relevance for other states considering legislation to increase adoption of clinical guidelines for opioid prescribing and pain care. The study will be conducted using measures constructed from Medicaid outpatient and prescription drug claims data (January 2017-December 2019) using CPT and ICD10 codes. It will employ an interrupted time series design with a comparison group (Colorado) which is a strong design. It controls for both secular trends and historical events occurring during the study period (July 2017- December 2018) that might also be associated with changes in the outcomes.