<p>Despite universal health coverage policies, diabetes management in resource-constrained settings remains challenging due to complex interactions between patient behaviours and systemic barriers. This study combines health behaviour theories with healthcare system constraints in an agent-based model to evaluate the influence of policy scenarios on type 2 diabetes patients’ self-management behaviours, blood glucose control, medication adherence, and hospital admissions within Ghana’s public health system. Using pattern-oriented modelling with multiple validation levels, the model integrates empirical evidence from clinical data, service provider expertise, and behavioural research to simulate how patients’ daily decisions about taking medicines, following lifestyle recommendations, and seeking healthcare interact with system-level factors like medicine availability and insurance coverage. We evaluate three public health scenarios: expanding insurance coverage, increasing medicine availability, and implementing a sugar-sweetened beverage tax. Our analysis indicates that a sustained 10% annual increase in insurance coverage over five years yields substantially greater improvements in blood glucose control and reduces hospital admissions compared to alternative scenarios. By integrating behavioural theories with system constraints to simulate patient decision-making, this modelling approach reveals how affordability and availability barriers interact to influence self-management behaviours and treatment outcomes in underserved populations. Our findings have implications for the operation of Ghana's national insurance scheme and diabetes service planning and delivery within the public health sector.</p>