This study employs a NARDL technique to examine the intricate relationship between health inputs and health outcomes in Nigeria spanning 2000 to 2023. Drawing on Grossman's health capital theory, the analysis dissects the impact of public and private health expenditures on infant mortality, maternal mortality, life expectancy, and an aggregate health outcome index. Findings reveal unexpected associations, with increases in public health expenditure positively linked to infant mortality rates, while private health expenditure exhibits a negative impact, aligning with theoretical expectations. However, both public and private health expenditures lack significant effects on maternal mortality rates, highlighting the need for targeted interventions in maternal healthcare. Moreover, while private health expenditure significantly contributes to improvements in life expectancy and overall health outcomes, public health expenditure shows no significant effects, indicating potential deficiencies in government healthcare infrastructure and spending allocation. The Granger causality tests reveal no significant causal links between health inputs and health outcomes, except for weak unidirectional causality from infant mortality to private health expenditure and private health expenditure to overall health outcome index. The study recommends targeted public spending, public-private partnerships, improved maternal healthcare, and tailored policies to address regional disparities in healthcare access across Nigeria.