The standard drug vocabulary consists of the following components found in figure 2.

•  Drug reference terminology RxNorm, maintained by the National Library of Medicine (NLM) – vocabulary_id 8
• Classifications for mechanism of action, physiological effect, chemical structure and indication/Contraindication: National Drug File-Reference Terminology (NDF-RT), developed by a consortium of the NLM, the U.S. Department of Veterans Affairs, Veterans Health Administration (VHA) and Appelon, Inc. – vocabulary_id 7
• Drug products and classes developed by the Department of Veterans Affairs (VA Product and VA Class) – vocabulary_id 28 and 32
• Two classifications for therapeutic class: The Anatomical Therapeutic Chemical (ATC) classification maintained by the WHO Collaborating Centre for Drug Statistics Methodology, vocabulary_id 21 and the Enhanced Therapeutic Classification (ETC), maintained by First Databank (FDB) – vocabulary_id 20
• Indication and Contraindications: FDA-approved and off-label indications as well as Contraindications are provided by First Databank (FDB Indications) – vocabulary_id 19.