Overview The Handbook of Pharmaceutical Excipients, 6th Edition (often referenced as "6th Ed.") is an authoritative, comprehensive reference guide detailing the physical and chemical properties, functions, safety, and regulatory status of pharmaceutical excipients. Jointly published by the American Pharmacists Association (APhA) and the Royal Pharmaceutical Society (RPS) , it remains an essential resource for formulation scientists, quality control analysts, regulatory affairs professionals, and pharmacy students.