The Association Between Patient Out-of-Pocket Medical Costs and Medication Adherence

Interventions to reduce cost-related medication nonadherence have focused on reducing out-of-pocket (OOP) prescription drug costs. However, little is known about the impact of OOP medical costs on adherence. This study examines the relationship between patient all-cause OOP medical costs and medication adherence.

A retrospective study was conducted using July 2017 to December 2018 Medicare Advantage data from the Optum Clinformatics Data Mart deidentified database. Inclusion criteria were adapted from the specifications of 3 medication adherence measures used in the Medicare Part D Star Ratings program: diabetes, renin-angiotensin system antagonists (RASAs), and statins.

Multivariable logistic regression models were used to assess the relationship between OOP medical costs and medication adherence across 4 mutually exclusive cohorts-diabetes only, RASA only, statins only, and diabetes-RASA-statins-after adjusting for covariates.

A total of 47,091, 443,831, 510,394, and 284,137 individuals were included in the diabetes-only, RASA-only, statins-only, and diabetes-RASA-statins cohorts, respectively. OOP medical costs were associated with a significant decrease in medication adherence across all cohorts. A $1000 increase in patient all-cause OOP medical costs reduced the odds of adherence by 7.3% (OR, 0.927; 95% CI, 0.919-0.935; P  < .001) for statins, 7.4% (OR, 0.926; 95% CI, 0.903-0.949; P  < .001) for diabetes medications, and 11.6% (OR, 0.884; 95% CI, 0.876-0.892; P  < .001) for RASAs. The negative impact of OOP medical costs on adherence was greatest in the diabetes-RASA-statins cohort.

Interventions aimed at improving medication adherence should focus on patient OOP prescription drug costs but should also consider the potential impact on adherence of total patient OOP costs incurred for all medical services.