Impact of a Pharmacy Copayment Increase on Medication Use in the Military Health System.

Background: We analyzed the impact of a copayment increase instituted February 1, 2018 for persons covered by the retail or mail order Military Health System (MHS) pharmacy benefit.

Methods: We compared medication use in 2 cohorts in the 12 months before and after the copayment increase: MHS beneficiaries between 18 and 64 years old (MHS cohort), and MHS beneficiaries older than or equal to 65 years old with Medicare (Medicare cohort). Subjects with diabetes, hypertension and hypercholesterolemia were eligible. Using propensity score matching, we compared the control group of those who obtained medications at military pharmacies ($0 copay) to those who experienced a copay increase. The outcome variable was any use of condition-specific medication.

Results: In the MHS cohort there were 30,753, 46,965, and 59,783 non-unique persons with diabetes, hyperlipidemia, and hypertension, respectively, in the intervention and control groups. In the Medicare cohort there were 45,977, 205,363, and 365,628 non-unique persons, respectively. The post-period mPDC differences for the MHS cohort were 0.02 (95% CI: 0.01, 0.03), 0.03 (95% CI: 0.02, 0.03), and 0.03 (95% CI: 0.01, 0.03) for the diabetes, hyperlipidemia, and hypertension cohorts, respectively. The post-period mPDC differences for the Medicare cohort were 0.01 (95% CI: 0.01, 0.02), 0.03 (95% CI: 0.03, 0.04), and 0.01 (95% CI: 0.01, 0.02), respectively.

Conclusions: The small (1-3 percentage point) copayment increases are unlikely to have had adverse clinical effects. Insurers and policy-makers should understand that even small copayment increases can impact the use of clinically important medications and should carefully consider the tradeoffs.