The following guideline is an extension of the Note for Guidance on Stability testing of New Drug Substances and Products (CPMP/ICH/2736/99 corr) and sets out the stability testing requirements for existing active substances and related finished products. For the purposes of this guideline, an existing active substance is one that has been authorised previously through a finished product within the European Community. This guideline is applicable to chemical active substances and related finished products, herbal drugs, herbal drug preparations and related herbal medicinal products and not to radiopharmaceuticals, biologicals and products derived by biotechnology.