What makes a requirement binding here
The Convention on the Elaboration of a European Pharmacopoeia, opened for signature on 22 July 1964 — an international treaty, which makes this the one entry on the harmonizer side of the axis whose output is genuinely binding rather than recommended. The Contracting Parties, now more than thirty European states together with the European Union, undertake to give the European Pharmacopoeia legal force in their territories. The Ph. Eur. is elaborated and published by the European Directorate for the Quality of Medicines & HealthCare, the Council of Europe body created under that Convention.
Directly, once a monograph is in force in a signatory state: the Ph. Eur. is the legally binding reference for the quality control of medicines and their ingredients, and a substance covered by a monograph must comply with it. This is the sharpest contrast on the whole axis — the United States Pharmacopeia acquires legal force through the FD&C Act and state adoption, whereas the Ph. Eur. acquires it through a treaty obligation the state itself signed. EDQM also operates the certification procedure that issues a Certificate of Suitability, the CEP.