Seniors who are enrolled in Medicare plans which require higher co-pays for certain medications fill 15 percent fewer prescriptions than seniors who have a flat co-pay for all meds, according to a new study. Researchers examined three-tier plans (users pay different co-pays for “preferred” or brand named drugs), and one-tiered plans (patients pay the same co-pay for all prescribed medications), and found that the three-tiered plan caused seniors to skip on important medications in order to save money.