Antihypertensive medication co-pay and adherence among Veterans receiving care within the Veterans Health Administration

Abstract: Background: Despite safe, effective, and relatively affordable antihypertensive therapies, blood pressure (BP) control remains suboptimal. One potential contributor is poor medication adherence. We determined if $0 in out-of-pocket costs for antihypertensive medication is associated with greater antihypertensive medication adherence among Veterans receiving healthcare within the Veterans Health Administration (VA). Methods: We performed a retrospective cohort study of Veterans receiving care at the VA from 2000 through 2022. We included Veterans with an incident hypertension diagnosis, new initiation of antihypertensive medication, and >12-months of follow-up for antihypertensive medication fills. Our exposure was co-pay status, which was indicated by each VETerans Priority Group and is determined by considering service-related disability. Veterans in Priority Group 1 (PG1) have $0 co-pay while those in Priority Group 2 (PG2) have small co-pays. Our outcomes were low medication adherence, defined as having a proportion of days covered (PDC) <80%, and medication discontinuation defined as having no fills for antihypertensive medication for the final 90 days of the 365 days after initiation. We utilized a Quasi-Poisson model with inverse probability weighting to estimate risk ratios (RR) and 95% confidence intervals (CI) for the relationship between co-pay status and medication adherence and discontinuation. Results: Among 540,642 Veterans (mean age 57.2 years, 8.3% female, 71.4% non-Hispanic White), 72.0% had no co-pay (PG1; n=389,515). Most Veterans had low adherence rates overall (PDC >80%): 31.5% in PG1 and 29.5% in PG2. After adjusting for covariates, adherence was higher among Veterans without a copay (RR 1.03, 95% CI 1.02-1.04), while discontinuation rates were lower (13.9% vs. 16.9%; RR 0.85, 95% CI 0.83-0.86). Conclusion: Veterans with no medication co-pay had higher adherence and lower discontinuation rates one year after starting antihypertensive medication. Small co-pays may affect medication adherence and discontinuation rates, suggesting that out-of-pocket costs, even modest ones, can be a barrier to proper antihypertensive medication use.