Abstract
IMPORTANCE: The adverse effects of prescription drug costs on medication adherence and health have been well described for individuals. Because many families share financial resources, high medication costs for one could lead to cost-related nonadherence in another; however, these family-level spillover effects have not been explored. OBJECTIVE: To evaluate whether the cost of a child's newly initiated medication was associated with changes in their parent's adherence to their own medications and whether that differed by likely duration of treatment. DESIGN, SETTING, AND PARTICIPANTS: This cohort study used interrupted time-series analysis with a propensity score-matched control group from a large national US health insurer database (2010-2020) and included children initiating medication and their linked presumed parents using long-term medications. EXPOSURE: The cost of the child's initiated medication. Child medication cost was classified based on highest (≥90th) or lowest (<10th) decile from out-of-pocket medication spending, stratified by whether the medication was intended for short- or long-term use. Children initiating high-cost medications (based on the highest decile) were propensity-score matched with children initiating low-cost medications. MAIN OUTCOME AND MEASURES: The child's parent's adherence to long-term medication assessed by the widely used proportion of days covered metric in 30-day increments before and after the child's first fill date. Parent demographic characteristics, baseline adherence, and length of treatment, and family unit size and out-of-pocket medication spending were key subgroups. RESULTS: Across 47 154 included pairs, the parents' mean (SD) age was 42.8 (7.7) years. Compared with a low-cost medication, initiating a high-cost, long-term medication was associated with an immediate 1.9% (95% CI, -3.8% to -0.9%) reduction in parental adherence sustained over time (0.2%; 95% CI, -0.1% to 0.4%). Similar results were observed for short-term medications (0.6% immediate change; 95% CI, -1.3% to -0.01%). Previously adherent parents, parents using treatment for longer periods, and families who spent more out-of-pocket on medications were more sensitive to high costs, with immediate adherence reductions of 2.8% (95% CI, -4.9% to -0.6%), 2.7% (95% CI, -4.7% to -0.7%), and -3.8% (95% CI, -7.2% to -0.5%), respectively, after long-term medication initiation. CONCLUSIONS AND RELEVANCE: In this cohort study small reductions in adherence across parents with higher child drug costs were observed. Health care systems should consider child-level or even household-level spending in adherence interventions or prescription policy design.