We examined a nationally representative sample of 30 964 individuals in the 2007 Medical Expenditure Panel Survey (MEPS).4 Our study population consisted of individuals older than 18 years who used any generic medications or their brand-name counterparts, available in $4 programs any time in 2007. We limited our analysis to pills, tablets, or capsules. To identify prescriptions for these medications filled through $4 programs in MEPS, we used the following criteria: (1) the drug was available through a $4 program at $4 for a 30-day quantity; (2) patients paid $4 out-of-pocket for the same 30-day quantity; and (3) no other payers contributed to the payment (ie, patients bore the total medication cost). We defined those who did not use $4 programs and could save if they filled their drugs (both generic or brand name) at $4 programs as “potential users” and calculated potential savings as the difference between MEPS actual prescription payments and potential costs if one were to buy the drugs from $4 programs. Because not every potential user would switch to a $4 program, we conducted sensitivity analyses. We ranked the potential out-of-pocket savings among potential users from highest to lowest and then calculated potential savings assuming only the top 80%, 50%, and 30% of potential users would switch.