Background: Universal health coverage (UHC) depends, among other things, on fair and efficient public financing. In many low- and middle-income countries (LMICs), fragmented health systems entrench inequalities by linking entitlements to employment status. In Mexico, persistent segmentation and institutional fragmentation have shaped the structure and distribution of public health financing, exemplifying this challenge through a dual public system that separates the population with social security from those without. While several policy reforms have sought to improve coverage and financial protection, little is known about the extent to which these efforts have influenced the equity of public resource allocation.
Objective: To quantify long-term trends and territorial inequalities in the allocation of public health expenditure between populations with and without social security across Mexico’s 32 states from 2000 to 2023.
Methods: We conducted a retrospective, state-level analysis of public health expenditure (PHE) from 2000 to 2023, expressed in constant Mexican pesos (MXN), using official administrative data. We disaggregated spending by population groups with and without social security coverage and estimated complementary measures of inequality and inequity, including allocation intensity, the Relative Equity Index (REI), the Slope Index of Inequality (SII), the Relative Kuznets Index (RKI), and concentration indices (CI). We then fitted generalised least squares (GLS) panel models to assess temporal and subnational trends in equity.
Results: Despite increases in total public health spending, PHE remained below the WHO-recommended threshold and was distributed inequitably between population groups. The population without social security—representing more than half of the national total population—consistently received lower per capita allocations. In 2000, public spending per capita for this group was MXN 2,670, compared to MXN 8,400 for the population with social security—over three times higher. Although the gap narrowed importantly over time, disparities persisted: by 2023, the ratio remained at 1.14 (MXN 4,960 vs. 4,350). REI values rarely exceeded 0.9 and declined after 2008, indicating sustained underfunding of the non–social security population. CI confirmed increasingly regressive patterns in resource distribution, particularly after 2014. Subnational inequities also deepened, with poorer states experiencing more pronounced deteriorations in equity indicators. Temporary gains observed during reform periods (e.g. 2004–2008, 2018–2021) proved fragile and were subsequently reversed.
Conclusions: Mexico’s public health financing system remains structurally biased against populations without formal coverage and fails to allocate resources in accordance with demographic weight or health need. Achieving equitable progress towards UHC will require a fundamental transformation of financing architecture, including integrated funding pools, binding redistributive mechanisms, stronger federal stewardship, and disaggregated, equity-sensitive monitoring systems.
Supplementary Information: The online version contains supplementary material available at 10.1186/s12939-025-02735-5.
Keywords: Fragmentation; Health expenditure; Inequalities; Mexico; Segmentation; Universal coverage.