Abstract
<jats:p>In February 2021, Oregon became the first US state to decriminalize possession of small amounts of all commonly used illicit drugs (Measure 110); twenty-four days later, Washington's Supreme Court Blake ruling produced a weaker, shorter-lived decriminalization. Evaluations of these policy periods have focused on overdose deaths, with contested results; their association with the mental health of the general population is unknown. Using surveillance data on 6.3 million adult interviews (2011-2024) and synthetic control methods with permutation inference, we find frequent mental distress an estimated 2.15 percentage points higher in Oregon than in its synthetic counterfactual (largest positive gap among 45 jurisdictions; two-sided rank 2/45, p = 0.044, though not significant under the alternative fit-normalized statistic), with directionally consistent estimates in Washington and a joint test on the pair at p = 0.015. The increase concentrates in self-reported distress, among women and young adults, and is not mirrored in diagnoses, police-recorded partner violence or suicide.</jats:p>