Each plan that offers prescription drug coverage through Medicare Part D must give at least a standard level of coverage set by Medicare. Plans can vary the list of prescription drugs they cover (called a formulary) and how they place drugs into different "tiers" on their formularies.
Anyone on Medicare (with either Part A or Part B) is entitled to drug coverage (known as Part D) regardless of income. No physical exams are required. You cannot be denied for health reasons or because you already use a lot of prescription drugs.