Patients with prescription drug coverage assume their copayment represents a portion of the total cost of the drug, with their insurer covering the difference. Yet, a new study finds overpayments, a situation in which the copayment is more than the cost of the drug, to be common. The researchers compared National Average Retail Price survey data from CMS from January to June 2013 with a 25 percent random sample of Optum’s Clinformatics Data Mart data from the same period. According to the study, 23 percent of all prescriptions analyzed involved an overpayment. The overpayment rate was higher for generics than brand drugs, 28.17 percent versus 5.95 percent. All-in-all, the average overpayment was $7.69, with 17 percent of overpayments exceeding $10. In a corresponding white paper, the researchers identify the 20 most popular prescription drugs during the study period, finding nine involved overpayments more than 40 percent of the time. These findings may not only have direct implications for overall drug spending but also may contribute to cost-related medication non-adherence which leads to higher medical expenditures and poorer health outcomes.