OBJECTIVES: Generic Drug Discount Programs (GDDPs) offer commonly used medications at low out-of-pocket cost, potentially reducing the cost barrier to access for many patients. The objectives of this study were to determine the national share of antidiabetic and antihypertensive prescriptions filled through a GDDP and to estimate the effects of various demographic and socioeconomic patient characteristics on GDDP use.  METHODS: Data were taken from the Medical Expenditure Panel Survey (MEPS). Patients who filled at least one prescription, over a two-year period, for an oral antidiabetic or antihypertensive medication were identified from the annual prescribed medicines files (2010-2013) and longitudinal panel files (2010-2011, 2011-2012, 2012-2013). Claims for these patients were considered GDDP-filled if the only recorded price paid was out-of-pocket, and the drug quantity dispensed and price matched those on published retail-chain GDDP lists. A logistic regression model was developed and estimated to explain whether a patient filled at least one of his or her prescriptions through a GDDP. Covariates included age, race, income, insurance type, geographic region, and number of medications. RESULTS: GDDP-filled prescriptions accounted for 15.1% of the 1,632,508,663 prescriptions filled between 2010 and 2013. Of the 193.2 million patients with any antidiabetic or antihypertensive claim over these same years, 38.3% (N=74,078,714) used a GDDP. Significant predictors of GDDP use were patients from the Midwest (OR=1.31; 95%CI 1.07-1.60) or South (OR=1.30; 95%CI 1.08-1.58) compared to the West; patients aged 40-49 (OR=1.40; 95%CI 1.15-1.71) or 50-64 (OR=1.40; 95%CI 1.21-1.60) compared to those 65 and older; and, uninsured patients (OR=2.88; 95%CI 2.30-3.60) or privately insured patients (OR=1.44; 95%CI 1.25-1.67) compared to those with public insurance.  CONCLUSIONS: The fact that uninsured patients were nearly 3 times more likely to use a GDDP than publicly insured patients suggests that the availability of low-cost medications via a GDDP may help to reduce the cost barrier to medication access.