Effects of two-tier prescription drug copayments on prescription drug use and expenditures among health maintenance organization commercial enrollees with diabetes

Background. There is limited information about how patient out-of-pocket costs might affect drug use and expenditures over time.;Methods. In a natural experiment (2001-2005), this study examined changes in mean annual drug expenditures for all drugs and four major essential drug therapies (oral antidiabetic, insulin, antihypertensive and antidyslipidemia drugs), and out-of-pocket drug expenditures. Drug expenditures included drug purchase cost and dispensing cost, and were standardized to adjust for drug price changes over time. This study also examined changes in mean annual days supplied of the major essential drug therapies. All 8224 subjects were commercially insured Health Maintenance Organization (HMO) enrollees with diabetes in January 2001, age 18+ years. Starting in 2002, 66% of subjects paid ;Results. This study reported difference-in-difference estimates (two-tier vs. one-tier for each post-treatment year relative to the baseline year, 2001) based on model results and mean values of covariates. For mean annual total drug expenditures, they were -;Conclusions. Two-tier copayments were associated with persistent decreases in both total drug expenditures and oral antidiabetic drug expenditures among patients with diabetes during the first four years with two-tier copayments. Two-tier copayments seemed to have decreased drug expenditures without significantly affecting days supplied of the major essential drug therapies. Additional research need to better understand underlying mechanisms of decreases in oral antidiabetic drug expenditures and clinical implications related to two-tier copayments.