If an analytical method for assay, related substances and degradation products of a combination product is intended to evaluate stability, the method will need to be proven to be stability indicating.   If the combination product contains a new drug, a forced degradation study will be needed.   If the combination product contains a generic drug, literature references to known degradation pathways and impurities can be used to evaluate if the method is stability indicating.   However, if the combining process is significantly different from the literature references, additional degradation pathways may need to be explored experimentally.