Impurites- Stability testing

[samkarthik_1983]

In Stability studies for Assay, the significant change is 5% from its initial value. Is there any specifications/limits/criteria for Related substances - Known and Unknown impurities?

[LC_labrat]

The stability guidance states for a drug product a significant change is any degradation product's exceeding its acceptance criterion. I'm not sure if you are asking about drug substance or drug product.