Medicare Part D is the newest addition to Medicare. Part D is the prescription drug plan. You must be enrolled in Medicare before you can apply for Part D coverage. Most people will pay a monthly premium for this coverage. Everyone with Medicare can get this coverage. It may help you lower prescription drug costs and help protect against higher costs in the future. Private companies provide the coverage. You choose the drug plan (there are many from which to choose) and pay a monthly premium. If you decide not to enroll in a drug plan when you are first eligible, you may have to pay a penalty if you join later.