One way health insurers control costs is to require a higher co-payment for brand-name drugs than for their generic equivalents. In some cases, an insurer may refuse to cover certain brand-name drugs altogether and offer coverage only for the generic equivalents.
In the vast majority of cases, the generic equivalent is a suitable (and less expensive) substitute for the brand-name medication. If your doctor feels that your condition requires the brand-name drug, but the drug is not covered under your prescription plan, ask your doctor to petition the insurer for coverage due to medical necessity. Your insurer may cover the brand-name drug after your doctor provides the facts of your case.