Massachusetts has the highest generic-drug dispensing rate at 51%, according to an Express Scripts study that measured per capita generic drug use in 2003. The study used a random sample of 3 million pharmacy benefit plan members aged 18 to 64. New Mexico and Oregon followed Massachusetts, with a dispensing rate of ~50%. Eastern states, such as New Jersey and New York, and southern states, including Texas, Louisiana, Florida, and Mississippi, used generics to fill fewer than 43% of all prescriptions. New Jersey used generics for fewer than 40% of all prescriptions.
As to why there are variations in generic fill rates, according to the study authors, possible explanations include variations in prescribing patterns, state regulations, differences in disease prevalence, and varying use of drug benefit designs that promote greater use of generics.