Each medicare Part D insurance company can decide what tier to put each drug on. Also they are not required to cover all drugs, but they do have to have at least one in each drug class. I see an insurance agent to find out changes in offerings by all the insurance companies in my state every November so that I can change if necessary. She makes sure all my medicines are covered under some tier. She also compares cost and coverage. For the last two years I have had the same vendor - HealthPartners - because I don't have a donut hole although my insurance cost is $300 a month and copays total $250... I have to keep remembering that if I didn't have insurance then I would have to pay out over $1300 per month on drugs, an impossible thing. If I had a lower cost supplemental plan with drug coverage then I would have to come up with $4000 over 3 months until I got to catastrophic coverage for medications. Medicare plans can be so confusing, especially if you are having other problems. That is why I let my insurance agent do the initial investigation into the plans each year.