Preventive Drug Lists Reduce Income-Related Disparities in Medication Adherence Over 2 Years: A Natural Experiment for Translation in Diabetes (NEXT-D) Study.

Background: Employers add Preventive Drug Lists (PDLs) to commercial insurance plans to reduce out-of-pocket payments for medicines that treat important chronic illnesses.

Objective: This study examined the impact of PDLs among patients with pre-existing diabetes.

Research design: Interrupted time series design with difference-in-difference analysis.

Subjects: We identified 5575 patients aged 12-64 with diabetes whose employers adopted PDL coverage for 2 years after a baseline year without; an equivalent number of matched and weighted controls were selected from employers that did not offer PDL plans.

Measures: Utilization, out-of-pocket payments, and medication adherence overall, among lower-income patients, and for those paying full cost for medicines under high-deductible plans.

Results: Compared with controls, patients with PDL coverage experienced large, statistically significant 35%-55% relative reductions in OOP payments. The PDL group experienced significant relative increases in 30-day fills in follow-up year 1 for noninsulin antidiabetics (+9.5) and a nonsignificant increase for insulin (+6.2%); these were matched by similar increases in percentage of days in which medicines were available. Increases were all substantially greater in the second follow-up year, larger among lower-income patients, and greatest by year 2 for lower-income patients in high-deductible plans with health savings accounts.

Conclusions: PDL coverage was associated with substantial reductions in OOP payments for medications to manage diabetes and cardiovascular risk. Patients on antidiabetic medications, especially those with lower incomes, experienced improvements in adherence, which grew over time.