The fundamental requirement for a generic drug is Bioequivalence. This means that the generic version must deliver the same amount of active ingredient into a patient's bloodstream at the same rate as the brand-name drug.
In 2026, regulatory agencies like the FDA and EMA require the generic drug's absorption rate to fall within a strict range (typically 80% to 125%) of the brand-name product. While the Active Pharmaceutical Ingredient (API) must be identical, generic manufacturers are allowed to use different inactive ingredients (excipients), such as binders, flavors, or colors. Because of trademark laws, generic pills are legally required to look different (shape, color, or size) from the original brand-name version, even though they perform exactly the same function.