The impact of multimorbidity and sociodemographic factors on cost-related medication nonadherence

BACKGROUND Access to prescription medications is a key determinant of chronic disease management and outcomes, yet cost can be a major barrier. OBJECTIVE The purpose of this study was to quantify cost-related medication non-adherence (CRMNA) and determine how CRMNA varied by sociodemographic and health factors. METHODS The 2021, 2022, and 2023 adult samples of the National Health Interview Survey (NHIS) were used. CRMNA was self-reported and defined at three intensity levels: high, some and low. Sociodemographic and health factors included age, race, education, income, multimorbidity, and geography. Chi-square tests assessed CRMNA differences by key sociodemographic and health factors, and a cumulative logit model evaluated associations between sociodemographic and health factors and CRMNA levels. RESULTS From 2021 to 2023, the prevalence of any CRMNA increased from 9.62% to 10.76%. In multivariable models, each additional chronic disease medication was associated with 36% higher odds of experiencing a greater level of CRMNA (aOR=1.36, 95% CI: 1.30-1.42; p=<.0001). Adults of two or more races had higher odds of CRMNA compared to Non-Hispanic White adults (aOR=1.59, 95% CI: 1.22-2.08; p=0.0007). Compared to adults aged 18-24, adults aged 25-34 had the highest odds of CRMNA (aOR: 1.76, 95% CI:1.37-2.28, p<.0001), while adults ≥65 had the lowest (aOR:0.53, 95% CI: 0.41-0.67, p<.0001). Compared to privately insured individuals, those with public insurance had 21% lower odds of CRMNA (aOR=0.79, 95% CI: 0.70-0.90, p=0.0004), while uninsured individuals had more than twice the odds (aOR=2.58, 95% CI: 2.16-3.09, p<0.0001). CONCLUSION This study highlights the disproportionate burden of CRMNA among racial minorities, and multi-morbid privately insured young adults. These groups are most vulnerable to the cumulative costs of chronic disease medications and may thus require clinical and policy strategies to minimize cost burden and improve adherence.