RxNorm is a standardized nomenclature for clinical drugs. RxNorm is produced by the National Library of Medicine (NLM). In this context, a clinical drug is a pharmaceutical product given to (or taken by) a patient with a therapeutic or diagnostic intend. The name of the drug in RxNorm combines its ingredients, dosage strength, and form. The RxNorm Source Information file contains a subset of the data distributed by NLM in the RXNSAB.RRF file. This file contains the sources for each of the RxNorm Files loaded into VistA and their restriction levels. There is one row in this file for every source in RxNorm that is represented in this RxNorm release.