Final answer:
The percentage of prescription drug costs that insured individuals must pay under Medicare Part D after reaching the initial benefit limit is known as the coverage gap, or "donut hole," which has been reduced due to phased-in discounts via the Affordable Care Act.
Step-by-step explanation:
After the initial benefit limit is reached under Medicare Part D, the percentage of prescription drug costs that the insured must pay is known as the coverage gap or "donut hole." Historically, beneficiaries were responsible for a larger portion of their drug costs within this gap. However, under the Affordable Care Act, discounts were phased in to reduce the patient's out-of-pocket costs for prescriptions while in the donut hole. Once a beneficiary reaches the out-of-pocket threshold, they exit the coverage gap and enter catastrophic coverage, where Medicare pays for the majority of drug costs, and the patient has a low co-payment. It's important to note that specific percentages can change yearly and depend on legislative adjustments.