I am on a Medicare Prescription Drug Plan that uses CVS, exclusively, as their "Preferred" Pharmacy Chain. That means I either have to fill my prescriptions at CVS, or pay significantly more to fill them at a different pharmacy. CVS refuses to fill my "Do Not Substitute" prescriptions as written (by my physicians). No good reason given by CVS pharmacist, just told me that CVS could not provide (generic) drugs manufactured by the pharmaceutical companies specified on my prescriptions, even though CVS does have the ability to do so (other more customer-centric drug store chains do this for their customers). Apparently, CVS would rather limit their customer base to people who will accept whatever CVS chooses to dispense... likely due to their focus being on profit, rather than on what is in a customer's best interest.