Why higher copayments for opioids did not reduce use among Medicare beneficiaries
研究医疗保险D部分计划提高阿片类药物共付额的效果，发现患者转向现金支付，总使用量未显著下降，因低成本仿制药和反回扣条款削弱了成本分摊的抑制作用。
To examine whether higher cost-sharing deterred prescription opioid use. Medicare Part D claims from 2007 to 2016 for a 20% random sample of Medicare enrollees. We obtain estimates of the effect of cost-sharing on prescription opioid use using ordinary least squares and instrumental variables methods. In both, we exploit the variation (change) in cost-sharing within plans over time for a sample of beneficiaries who remain in the same plan. Focusing on changes in cost-sharing within a plan for a constant sample of beneficiaries mitigates potential bias from plan selection and using a constant set of weights derived from use in year (t) eliminates changes in the cost-sharing indexes due to (endogenous) consumer choice in year (t+1). Part D plans adopted benefit changes designed to reduce opioid use, including moving opioids to higher cost-sharing tiers. Increasing plan copayments for hydrocodone or oxycodone was associated with reductions in plan-paid claims and offsetting increases in cash claims. Widespread availability of low-cost generics combined with the anti-clawback provision in Part D mediated the effect of higher cost sharing to curb opioid use. As plans moved generic opioids to higher cost-sharing tiers, beneficiaries simply paid cash prices and aggregate use remained largely unchanged. The anti-clawback provision in Part D, intended to protect beneficiaries from price gouging, limited plans' ability to constrain opioid use through typical demand-side measures such as increased cost-sharing.