OBJECTIVES: The aim of this paper is to model the age, gender and regional pattern of GMS coverage rates as they are key determinants of public spending on GMS medicines.  METHODS: We used PCRS (Primary Care Reimbursement Service) and CSO (Central Statistics Office) databases to estimate GMS coverage rates by age, gender and region in 2010 and 2011.  Assuming log-normally distributed incomes we used CSO SILC data to estimate GMS coverage semi-elasticities in 2010. We estimated how much GMS male and female coverage rates in 7 adult age categories and 8 Irish regions in 2010 responded to changing average income levels, income inequality and income thresholds. We tracked how well our predicted GMS coverage rates fitted actual rates in 2011. We simulated the 2011 GMS medicines cost burden of a ceteris paribus repeat of the 2010 changes in income and income-inequality. RESULTS: Our modelled coverage rates have high goodness of fit compared to conventional econometric estimates. Coverage income-semi-elasticity ranges from .7 to 2.3, is highest for elderly age cohorts and in the South-East and South-West regions and is similar for males and females.  Growing inequality generally increases GMS coverage but pushes some persons aged over 70 above the qualifying income threshold. Repeating 2010 average income in 2011 would increase the 2011 GMS medicines cost by around €110m; repeating the 2010 inequality changes would increase it by a further €105m, ceteris paribus.    CONCLUSIONS: Fiscal cutbacks during recession induce countervailing increases in the medical card population and the public cost of its medicines. These are the first systematic and detailed estimates – by age, gender and region – of whose medical access is affected and how much the offsetting public cost will increase.