You can go with a traditional Medicare plan or you are offered to go through an Insurance Company. The Insurance plan you go through includes a part D plan. By having my Medicare through Humana, only places that except Humana will take me as a patient. Believe me I have tried. Each plan offered by your Insurance Company's policy (part D) has different tier systems on their medications. The Medicare Insurance plans vary from carrier to carrier. You have pick the one that most closely addresses your needs and what most medical facilities will except in your area. I had a medical office quit seeing me when I switched from my Medicare plan through Blue Cross Blue Shield to my Medicare plan through Humana because they would except a Blue Cross but not Humana. You are allowed to kick in extra for a better plan while Medicare pays for the base plan. That is why every October, you get a booklet in the mail to evaluate each plan offered and you can change carriers from October to January 1st. The plans can change year to year. My first plan through Blue Cross Blue shield was at first wholly subsidized by Medicare. After the first year, they started to charge an extra amount over what they got from the government. I believe it was something like 35.00 a month for the exact plan I had the previous year at no cost to me. That is when I switched to a Humana plan wholly subsidized by Medicare.