For the fifth Market Surveillance Study on Suspected Illegal Products (MSSIP005), the General European OMCL Network (GEON) decided to carry out a combined retrospective and prospective study on Suspected Illegal Products containing Active Pharmaceutical Ingredients (APIs) that are not described in the Anatomical Therapeutic Chemical (ATC) classification system – International Non-Proprietary Name (INN) list. Some of the described cases are not related to medicines by presentation and therefore normally fall out of the scope of market surveillance of medicines in Europe.