A chemically equivalent copy of a brand-name drug, generic drugs are pharmaceutically and therapeutically the same as brand-name drugs. Not all brand-name drugs have a generic equivalent.
Generic drugs usually cost less than brand-name drugs. You can ask your doctor to prescribe a generic (if available) or prescribe the least expensive medication available.
If you purchase a brand-name drug when a generic alternative is available (regardless of the reason), you will pay your generic copay plus the cost difference between the brand-name and the generic drug.