Effect of cost sharing on prescription drug use by Medicare beneficiaries prior to the Medicare Drug Benefit and potential adverse selection in the benefit

Objectives: To (1) describe prescription drug cost sharing and benefit structures faced by seniors before implementation of the Medicare drug benefit, (2) examine the relationship between prescription drug benefit structure and prescription drug use by seniors prior to Medicare drug benefit, and (3) examine factors predicting intention to enroll in the Medicare drug benefit. Design: Cross-sectional study. Setting: Internet-based survey administered on behalf of the researchers by Harris Interactive in October 2005. Participants: Harris Interactive maintains a panel of individuals who have opted to participate in online surveys. Individuals from this panel who were English speaking, 65 years of age or older, U. S. residents, and enrolled in Medicare were invited to participate. Intervention: The survey collected information on prescription coverage, prescription use, intention to enroll in the Medicare drug benefit, health status, and demographics. Main outcome measures: Number of prescriptions used by a beneficiary in the month before the survey and the intention of the beneficiary to enroll in the Medicare drug benefit. Results: Beneficiaries were enrolled in plans with a wide variety of benefit structures and cost-sharing amounts. Prescription drug use fell with higher copayment ranks and average coinsurance but not at the P < 0.05 level. Among poorer individuals, the relationship between copayment rank and use was significant. Individuals reporting worse health status and a higher number of prescriptions indicated greater intention to enroll in the Medicare drug benefit, suggesting possible adverse selection. Conclusion: Prescription use decreased as cost sharing increased with mixed significance. There was evidence of potential adverse selection in the Medicare drug benefit.