Medication and Acute Care Use in Young Adults With Opioid Use Subject to Medicaid Prescription Caps.

Importance: State Medicaid prescription cap policies (ie, limiting the monthly number of covered prescriptions) may impede access to medications for opioid use disorder (OUD) and other chronic conditions. Yet, these policies remain understudied among those who become subject to caps at age 21 years. Objective: To evaluate the association of prescription cap policies with medication and acute care use among young adults with OUD. Design, Setting, and Participants: This study identified a cohort of young adults diagnosed with OUD using T-MSIS Analytic Files from January 1, 2016, to December 31, 2021. Data analysis was conducted from July 2025 to December 2025. The study compared outcomes between prescription cap and noncap states using a difference-in-differences analysis where a 2-month policy phase-in window was applied before and after age 21 years and effects estimated across the full follow-up period and the early (months 3-6), mid (months 7-9), and late (months 10-12) periods since the 21st birthday. Exposures: Becoming exposed to prescription caps at age 21 years. Main Outcomes and Measures: Monthly use (any and count) of buprenorphine, overall prescriptions, inpatient hospitalizations, and emergency department (ED) visits 12 months before vs after participant reached the age of 21. Results: This study analyzed 15 526 individuals from 26 non-prescription cap states and 1769 from 8 states with prescription cap policies. Most individuals were female (noncap states, 8156 [52.5%]; cap states, 1033 [58.4%]) and White (noncap states, 9512 [61.3%]; cap states, 705 [39.9%]). The baseline monthly prevalence for noncap and cap states was 39.3% vs 40.2% for any prescription receipt, 7.5% vs 3.1% for buprenorphine receipt, 3.2% vs 4.8% for hospitalizations, and 14.1% vs 18.7% for ED visits. After adjustment, cap policies were associated with a 4.7% (95% confidence limit [CL], -9.9% to -0.2%) lower prevalence of any prescription receipt and 12.7% (95% CL, -18.7%, -6.7%) fewer total monthly prescriptions 10 to 12 months after participants reached the age of 21. Cap states had more hospitalizations during postperiod months 10 to 12 (6.0%; 95% CL, 0.3%-10.0%) and more ED visits in postperiod months 3 to 6 (4.7%; 95% CL, 1.0%-10.0%) and months 7 to 9 (8.3%; 95% CL, 3.3%-13.3%). Buprenorphine use did not significantly change after cap implementation. Conclusions and Relevance: In this cohort study, Medicaid prescription caps were associated with lower overall use of prescription medications and greater frequency of acute care use among young adults with OUD.