Combined Effect of Income and Medication Adherence on Mortality in Newly Treated Hypertension: Nationwide Study of 16 Million Person‐Years

Background Low socioeconomic status and poor medication adherence are known to be associated with increased morbidity and mortality among patients with hypertension, but their combined effects have not been studied. We therefore evaluated the joint association of household income and medication adherence with death and cardiovascular disease in patients newly treated for hypertension. Methods and Results This was a nationwide cohort study using the Korean National Health Insurance database. We included 1 651 564 individuals, aged 30 to 80 years, with newly treated hypertension and no prior cardiovascular disease and followed them for 10 years. Main exposures were household income in quintiles and adherence to antihypertensive medication, estimated by medication possession ratio: good (≥0.8), moderate (0.5 to <0.8), or poor (<0.5). The primary outcomes were all-cause and cardiovascular deaths. Higher mortality risk was observed in patients with low income (adjusted hazard ratio=1.50, 99% CI=1.46-1.53; lowest versus highest quintile) and poor medication adherence (adjusted hazard ratio=1.66, 99% CI=1.63-1.68; poor versus good adherence). When compared with the highest-income and good-adherence group, adjusted hazard ratio (99% CI) of death was 1.56 (1.52-1.61) for highest-income poor-adherers, 1.46 (1.41-1.51) for lowest-income good-adherers, and 2.46 (2.38-2.54) for lowest-income poor-adherers (P for interaction <0.001). Conclusions Low socioeconomic status and poor adherence to antihypertensive medication are associated with increased mortality and cardiovascular disease risks, but patients with low income are subject to larger excess risks by nonadherence. This highlights the potential importance of promoting medication adherence for risk reduction, especially in low-income patients with hypertension.