Does Decriminalization Prevent Overdose? Long-run Evidence and Methodological Examination of Measure 110

• In Event: Drugs and Alcohol

Abstract

In February 2021, Oregon implemented Measure 110 (M110), the first statewide policy in the U.S. to decriminalize possession of small quantities of illicit drugs. This paper replicates and extends existing evaluations of M110’s effect on overdose mortality, all of which rely on variants of the Synthetic Control Method (SCM). We show that short-run estimates vary primarily due to differences in the definition of overdose mortality—specifically, unintentional versus all-cause overdose deaths—rather than implementation or data discrepancies.

Extending the analysis through 2023, we find consistent evidence of a statistically significant increase in overdose mortality in Oregon. Monthly average treatment effects range from 0.60 to 0.77 additional deaths per 100,000 population—representing a 30–37% increase relative to the pre-policy baseline. We also reexamine the claims made in Zoorob et al. (2024), which attempt to control for synthetic opioid saturation in the illicit drug market. We outline the assumptions required for their approach and test the robustness of their findings across alternative pre-treatment periods and more direct proxies for fentanyl supply, including per-capita seizure rates. 

Our analysis includes a comprehensive battery of robustness checks: alternative inference procedures, leave-one-out tests, donor weight perturbations, pre-COVID matching, and multiple SCM variants including augmented synthetic control, synthetic difference-in-differences, and two-way fixed effects. While we find credible evidence of adverse mortality outcomes,  our analysis is necessarily limited to the unique context of Oregon’s implementation of decriminalization, including its imperfections. Our results reflect the policy as it was enacted in Oregon, rather than decriminalization in the abstract. We underscore the limitations of what this study can credibly identify in terms of causal inference, and emphasize the need for future work examining other dimensions of the policy to fully assess its broader impacts and overall benefit.

Authors

• David Michael Hall, University of Oregon
  Presenting Author

• Kyutaro Matsuzawa, San Diego State University
  Non-Presenting Co-Author

• Benjamin Hansen, University of Oregon
  Non-Presenting Co-Author