Importance: In the US, the COVID-19 pandemic led to a significant rise in unemployment and economic loss that disproportionately impacted low-income individuals. It is unknown how health care and prescription medication affordability changed among low-income adults during the COVID-19 pandemic overall and compared with their higher-income counterparts., Objective: To evaluate changes in health care affordability and prescription medication affordability during the COVID-19 pandemic (2021 and 2022) compared with pre-COVID-19 pandemic levels (2019) and whether income-based inequities changed., Design, Setting, and Participants: This retrospective cross-sectional study included adults 18 years and older participating in the National Health Interview Survey (NHIS) in 2019, 2021, and 2022. Low-income adults were defined as having a household income of 200% or less of the federal poverty level (FPL); middle-income adults, 201% to 400% of the FPL; and high-income adults, more than 400% of the FPL. Data were analyzed from June to November 2023., Main Outcomes and Measures: Measures of health care affordability and prescription medication affordability., Results: The study population included 89 130 US adults. Among the weighted population, 51.6% (95% CI, 51.2-52.0) were female, and the mean (SD) age was 48.0 (0.12) years. Compared with prepandemic levels, during the COVID-19 pandemic, low-income adults were less likely to delay medical care (2022: 11.2%; 95% CI, 10.3-12.1; 2019: 15.4%; 95% CI, 14.3-16.4; adjusted relative risk [aRR], 0.73; 95% CI, 0.66-0.81) or avoid care (2022: 10.7%; 95% CI, 9.7-11.6; 2019: 14.9%; 95% CI, 13.8-15.9; aRR, 0.72; 95% CI, 0.64-0.80) due to cost, while high-income adults experienced no change, resulting in a significant improvement in income-based disparities. Low-income and high-income adults were less likely to experience problems paying medical bills but experienced no change in worrying about medical bills during the COVID-19 pandemic compared with prepandemic levels. Across measures of prescription medication affordability, low-income adults were less likely to delay medications (2022: 9.4%; 95% CI, 8.4-10.4; 2019: 12.7%; 95% CI, 11.6-13.9; aRR, 0.74; 95% CI, 0.65-0.84), not fill medications (2022: 8.9%; 95% CI, 8.1-9.8; 2019: 12.0%; 95% CI, 11.1-12.9; aRR, 0.75; 95% CI, 0.66-0.83), skip medications (2022: 6.7%; 95% CI, 5.9-7.6; 2019: 10.1%; 95% CI, 9.1-11.1; aRR, 0.67; 95% CI, 0.57-0.77), or take less medications (2022: 7.3%; 95% CI, 6.4-8.1; 2019: 11.2%; 95% CI, 10.%-12.2; aRR, 0.65; 95% CI, 0.56-0.74) due to costs, and these patterns were largely similar among high-income adults. Improvements in measures of health care and prescription medication affordability persisted even after accounting for changes in health insurance coverage and health care use. These patterns were similar when comparing measures of affordability in 2021 with 2019., Conclusions and Relevance: Health care affordability improved for low-income adults during the COVID-19 pandemic, resulting in a narrowing of income-based disparities, while prescription medication affordability improved for all income groups. These findings suggest that the recent unwinding of COVID-19 pandemic-related safety-net policies may worsen health care affordability and widen existing income-based inequities.