Decreased Gabapentin Prescription Fills Among Medicaid Enrollees Following State-Level Schedule V Controlled Substance Classification in Kentucky and West Virginia

BACKGROUND: Driven by concerns of gabapentin misuse and other harms, Kentucky (KY) and West Virginia (WV) became the first states to classify gabapentin as a schedule V controlled substance in July 2017 and June 2018, respectively. This study examined the association of these policies with gabapentin utilization among Medicaid beneficiaries. METHODS: Using a controlled interrupted time series design, we modeled a segmented generalized least squares regression and calculated the immediate and trend changes of gabapentin prescriptions among Medicaid enrollees in 2 states (KY, WV), separately. North Carolina (NC) was used as a control to account for secular changes; there was no controlled substance designation for gabapentin in NC during the study period. Total outpatient prescriptions per quarter (Q) were calculated from Medicaid's publicly available State Drug Utilization Data, and rates were established using state-specific combined Medicaid and CHIP average enrollment for the period 2016 to 2019. Multiple sensitivity analyses were performed, including a phase-in period model and internal negative control model, to assess robustness of results. RESULTS: Overall, utilization rates of gabapentin were higher in KY and WV relative to NC throughout the study period. The gabapentin controlled substance classification in KY was associated with a sustained decrease in trend (-10.6 prescriptions per 1000 enrollees per quarter; 95% CI: -13.6, -7.6) relative to NC. An immediate decrease in prescription rate (-18.9 prescriptions per 1000 enrollees; 95% CI: -32.7, -5.1) and a sustained decrease in trend (-3.8 prescriptions per 1000 enrollees per quarter; 95% CI: -7.1, -0.5) was observed in WV relative to NC. CONCLUSIONS: Our results show an association between decreased gabapentin utilization among Medicaid enrollees and classifying gabapentin as a schedule V controlled substance in KY and WV. Future research should focus on fully understanding the policy's impact on other populations and potential unintended or downstream effects.