Financial protection in flux: longitudinal evidence on out-of-pocket spending among middle-aged and older Mexicans...

Mexico is ageing rapidly, placing growing strain on health financing and long-term care systems. Older adults face a double burden: higher healthcare needs due to chronic conditions and multimorbidity, and limited or informal income in later life, leaving them highly exposed to out-of-pocket (OOP) spending. In 2020, the government replaced 'Seguro Popular' (SP) with the 'Instituto de Salud para el Bienestar' (INSABI) to strengthen financial protection, but its implications on older adults remain unclear. We analysed OOP among 13 616 individuals aged ≥50 years in the Mexican Health and Aging Study, interviewed in 2018 and 2021. Expenditures for hospitalizations, outpatient procedures, medical visits and medications in the previous 12 months were indexed to inflation and converted to 2021 US dollars. Tobit models estimated total and component OOP, including an interaction between insurance category (Uninsured; Social Security-IMSS/ISSSTE/PEMEX/Defence; SP 2018/INSABI 2021; Other) and survey year, adjusting for sociodemographic and health covariates. Between 2018 and 2021 the proportion of older adults reporting no health insurance tripled from 9.5% to 27.2%, while SP affiliation fell from 30.1% to 10.9%. Social Security beneficiaries spent substantially less than the uninsured on total OOP (about US$1 033 less in 2018 and US$539 less in 2021). SP in 2018 and INSABI in 2021 were also associated with lower OOP (-US$291 and -US$298 versus the uninsured, respectively). Only Social Security was associated with a statistically significant reduction in medication-related OOP. Overall, the transition from SP to INSABI coincided with a marked rise in reported uninsurance and persistently high OOP, particularly for medicines, the principal driver of financial burden among older adults. These findings highlight the fragility of recent health financing reforms and the need to ensure sustained, employment-independent financial protection for Mexico's ageing population.