Multiple brands of the same active ingredient may be available for the same strength, administration route and dose form. Generic brands needs to demonstrate bioequivalence to the originator brand, but the appearance of the generic and originator brands are not required to match. This variation is possible because different brands may vary in the excipients used in the formulation. Excipients are inactive ingredients, and typically make up about 90% of the formulation of an individual medication. Individual preferences or requirements may affect tolerance of particular excipients, such as the use of animal products. The different appearance of brands can affect medication management for some people. This review discusses the potential for excipients to alter the individual response to or tolerance of a medication brand.