In Medicare Part D, the six protected classes policy protects vulnerable seniors and low-income beneficiaries with serious and complex health conditions, while also allowing Part D insurance plans to use the tools they need to control costs. Medicines for some of the sickest patients in Part D are covered within the six protected classes, including those for cancer, epilepsy, HIV/AIDS and mental illness. Many of these conditions require patients to attempt a variety of therapies before they and their doctor settle on the most appropriate treatment, so there is no one-size fits all medicine for these conditions.