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Medical Terminologies at NLM

  • MeSH

    MeSH is the National Library of Medicine's controlled vocabulary thesaurus. It consists of sets of terms naming descriptors in a hierarchical structure that permits searching at various levels of specificity. The MeSH thesaurus is used by NLM for indexing articles for the MEDLINE/PubMED® database and for the NLM-produced database that includes cataloging of books, documents, and audiovisuals acquired by the Library. MeSH, in machine-readable form, is provided at no charge via electronic means.

  • UMLS

    The Unified Medical Language System (UMLS) integrates and distributes key terminology, classification and coding standards, and associated resources to promote creation of more effective and interoperable biomedical information systems and services, including electronic health records. All UMLS Knowledge Sources and associated software tools are free of charge to U.S. and international users.

  • RxNorm

    RxNorm provides normalized names for clinical drugs and links its names to many of the drug vocabularies commonly used in pharmacy management and drug interaction software, including those of First Databank, Micromedex, MediSpan, Gold Standard Alchemy, and Multum. By providing links between these vocabularies, RxNorm can mediate messages between systems not using the same software and vocabulary. RxNorm files are available through the NLM download server.


    SNOMED Clinical Terms (SNOMED CT) is an extensive clinical terminology that was formed by the merger, expansion, and restructuring of SNOMED RT® (Reference Terminology) and the United Kingdom National Health Service (NHS) Clinical Terms (also known as the Read Codes). It is the most comprehensive clinical vocabulary available in English (or any language). SNOMED CT is concept-oriented and has an advanced structure that meets most accepted criteria for a well-formed, machine-readable terminology. It has been designated as a US standard for electronic health information exchange in Interoperability Specifications produced by the Healthcare Information Technology Standards Panel and has also been adopted for use by the U.S. Federal Government, through the Consolidated Health Informatics (CHI) Initiative, for several clinical domains. NLM distributes SNOMED CT in multiple formats and makes it available free of charge to anyone in the U.S.

  • MedlinePlus Consumer Health Topic Vocabulary

    MedlinePlus is the National Institutes of Health's Web site for patients and their families and friends. It is produced by the National Library of Medicine. MedlinePlus uses a custom consumer health vocabulary for its 850+ health topics. Associated vocabulary terms (including synonyms, see references, and MeSH headings) are available for each health topic via an XML file. Not all topics include all types of terms. XML vocabulary files are freely available via the MedlinePlus Web site.