Answered By: Kathleen Hutchison
Last Updated: Nov 16, 2018     Views: 1254

MEDLINE is the largest component of PubMed (, the freely accessible online database of biomedical journal citations and abstracts created by the U.S. National Library of Medicine (NLM®). Approximately 5,400 journals published in the United States and more than 80 other countries have been selected and are currently indexed for MEDLINE. A distinctive feature of MEDLINE is that the all records are indexed with NLM's controlled vocabulary, the Medical Subject Headings (MeSH®).

In addition to MEDLINE citations, PubMed also contains:

  • In-process citations which provide a record for an article before it is indexed with MeSH and added to MEDLINE or converted to out-of-scope status.
  • Citations that precede the date that a journal was selected for MEDLINE indexing (when supplied electronically by the publisher).
  • Some OLDMEDLINE citations that have not yet been updated with current vocabulary and converted to MEDLINE status.
  • Citations to articles that are out-of-scope (e.g., covering plate tectonics or astrophysics) from certain MEDLINE journals, primarily general science and general chemistry journals, for which the life sciences articles are indexed with MeSH for MEDLINE.
  • Citations to some additional life science journals that submit full text to PubMedCentral® and receive a qualitative review by NLM.
  • Citations to author manuscripts of articles published by NIH-funded researchers.
  • Citations for a subset of books available on the NCBI Bookshelf (a citation for both the book and each chapter or section of the book).

One of the ways users can limit their retrieval to MEDLINE citations in PubMed is by selecting MEDLINE from the Subsets menu on the Limits screen.

Other PubMed services include:

  • Links to many sites providing full text articles and other related resources
  • Clinical queries and Special queries search filters
  • Links to other citations or information, such as those to related articles
  • Single citation matcher
  • The ability to store collections of citations, and save and automatically update searches
  • A spell checker
  • Filters to group search results

NLM distributes all but approximately 2% of all citations in PubMed to those who formally lease MEDLINE from NLM.