Abstract
BACKGROUND: There is considerable evidence that medication non-adherence is associated with higher healthcare costs. Payers and providers often target adherence quality measures for intervention, but the impact may depend on the medication. This study sought to assess differences in the relationship between medication adherence and medical (i.e., non-pharmacy) costs across three quality measures in a Medicare Advantage sample. METHODS: An observational study was conducted among cohorts of Medicare Advantage beneficiaries using the 2018-19 Optum’s de-identified Clinformatics(®) Data Mart Database. Cohort assignment was based on inclusion in one or all three of the Pharmacy Quality Alliance’s adherence measures for (1) renin-angiotensin-system antagonists, (2) statin, and (3) diabetes medications. Medication adherence was measured in year 1 and payer medical costs were measured in year 2. Generalized linear modeling (Gamma distribution and a log link) with interaction terms and coefficient contrasts were used to assess the relationship between adherence and subsequent payer medical costs, and to evaluate differences in this relationship across the three measures. Analyses were adjusted for sociodemographic, clinical, prescription-related, and insurance-related variables. RESULTS: The single-measure cohort included 1,001,316 beneficiaries, and the three-measure cohort consisted of 284,137 beneficiaries. There were negative relationships (p < 0.0001) between adherence and payer medical costs for all medication classes. These associations were stronger for diabetes medications (0.9808; p < 0.0001), followed by renin-angiotensin-system antagonists (0.9874; p < 0.0001) and statin medications (0.9919; p < 0.0001) in the single-measure cohort. The findings were similar among beneficiaries using all three medication classes. CONCLUSIONS: Better adherence was associated with lower payer medical costs across several therapeutic areas, providing additional evidence of the importance of adherence in managing health care costs. The relationship between adherence and subsequent year medical costs appears stronger for diabetes medications relative to renin-angiotensin-system antagonists or statins. Further research may explore interventions to increase adherence to diabetes medications to improve diabetes management. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12913-025-13331-2.