Last updated
ProducerU.S. National Library of Medicine (United States)
Languages40 languages for current journals, 60 for older journals
Disciplines Medicine, nursing, pharmacy, dentistry, veterinary medicine, health care, biology, biochemistry, molecular evolution, biomedicine, history of medicine, health services research, AIDS, toxicology and environmental health, molecular biology, complementary medicine, behavioral sciences, chemical sciences, bioengineering, health policy development, environmental science, marine biology, plant and animal science, biophysics
Record depthNLM Medical subject headings, abstracts, indexing,
Format coverageMostly academic journals; a small number of newspapers, magazines, and newsletters; over 40% are for cited articles published in the U.S., about 93% are published in English
Temporal coverage1946-present
No. of recordsOver 26 million
Update frequencyDaily; 2,000-4,000 references per update

MEDLINE (Medical Literature Analysis and Retrieval System Online, or MEDLARS Online) is a bibliographic database of life sciences and biomedical information. It includes bibliographic information for articles from academic journals covering medicine, nursing, pharmacy, dentistry, veterinary medicine, and health care. MEDLINE also covers much of the literature in biology and biochemistry, as well as fields such as molecular evolution.


Compiled by the United States National Library of Medicine (NLM), MEDLINE is freely available on the Internet and searchable via PubMed and NLM's National Center for Biotechnology Information's Entrez system.


MEDLARS (Medical Literature Analysis and Retrieval System) is a computerised biomedical bibliographic retrieval system. It was launched by the National Library of Medicine in 1964 and was the first large scale, computer based, retrospective search service available to the general public. [1]

Initial development of MEDLARS

Since 1879, the National Library of Medicine had published Index Medicus , a monthly guide to medical articles in thousands of journals. The huge volume of bibliographic citations was manually compiled. In 1957 the staff of the NLM started to plan the mechanization of the Index Medicus, prompted by a desire for a better way to manipulate all this information, not only for Index Medicus but also to produce subsidiary products. By 1960 a detailed specification was prepared and by the spring of 1961 a request for proposals was sent out to 72 companies to develop the system. As a result, a contract was awarded to the General Electric Company. A Minneapolis-Honeywell 800 computer, which was to run MEDLARS, was delivered to the NLM in March 1963, and Frank Bradway Rogers (Director of the NLM 1949 to 1963) said at the time "..If all goes well, the January 1964 issue of Index Medicus will be ready to emerge from the system at the end of this year. It may be that this will mark the beginning of a new era in medical bibliography."

MEDLARS cost $3 million to develop and at the time of its completion in 1964, no other publicly available, fully operational electronic storage and retrieval system of its magnitude existed. The original computer configuration operated from 1964 until its replacement by MEDLARS II in January 1975. [2] [3]


In late 1971, an online version called MEDLINE ("MEDLARS Online") became available as a way to do online searching of MEDLARS from remote medical libraries. [4] This early system covered 239 journals and boasted that it could support as many as 25 simultaneous online users (remotely logged-in from distant medical libraries) at one time. [5] However, this system remained primarily in the hands of libraries, with researchers able to submit pre-programmed search tasks to librarians and obtain results on printouts, but rarely able to interact with the NLM computer output in real-time. This situation continued through the beginning of the 1990s and the rise of the World Wide Web.

In 1996, soon after most home computers began automatically bundling efficient web browsers, a free public version of MEDLINE was instigated. This system, called PubMed, was offered to the general online user in June, 1997, when MEDLINE searches via the Web were demonstrated. [5]


The database contains more than 26[ needs update ] million records [6] from 5,639[ needs update ] selected publications [7] covering biomedicine and health from 1950 to the present.[ timeframe? ] Originally, the database covered articles starting from 1965, but this has been enhanced, and records as far back as 1950/51 are now available within the main index. The database is freely accessible on the Internet via the PubMed interface and new citations are added Tuesday through Saturday. For citations added during 1995-2003: about 48% are for cited articles published in the U.S., about 88% are published in English, and about 76% have English abstracts written by authors of the articles. The most common topic in the database is Cancer with around 12% of all records between 1950-2016, which have risen from 6% in 1950 to 16% in 2016. [8]


MEDLINE uses Medical Subject Headings (MeSH) for information retrieval. Engines designed to search MEDLINE (such as Entrez and PubMed) generally use a Boolean expression combining MeSH terms, words in abstract and title of the article, author names, date of publication, etc. Entrez and PubMed can also find articles similar to a given one based on a mathematical scoring system that takes into account the similarity of word content of the abstracts and titles of two articles. [9]

MEDLINE added a "publication type" term for “randomized controlled trial” in 1991 and a MESH subset “systematic review” in 2001. [10]


MEDLINE functions as an important resource for biomedical researchers and journal clubs from all over the world. Along with the Cochrane Library and a number of other databases, MEDLINE facilitates evidence-based medicine. [11] [12] [13] Most systematic review articles published presently build on extensive searches of MEDLINE to identify articles that might be useful in the review. [11] [12] MEDLINE influences researchers in their choice of journals in which to publish. [13]

Inclusion of journals

More than 5,200 biomedical journals are indexed in MEDLINE. [11] New journals are not included automatically or immediately. Several criteria for selection are applied. [14] Selection is based on the recommendations of a panel, the Literature Selection Technical Review Committee, based on scientific scope and quality of a journal. [15] The Journals Database (one of the Entrez databases) contains information, such as its name abbreviation and publisher, about all journals included in Entrez, including PubMed. [16]


PubMed usage has been on the rise since 2008. In 2011, PubMed/MEDLINE was searched 1.8 billion times, up from 1.6 billion searches in the previous year. [17]

A service such as MEDLINE strives to balance usability with power and comprehensiveness. In keeping with the fact that MEDLINE's primary user community is professionals (medical scientists, health care providers), searching MEDLINE effectively is a learned skill; untrained users are sometimes frustrated with the large numbers of articles returned by simple searches. Counterintuitively, a search that returns thousands of articles is not guaranteed to be comprehensive. Unlike using a typical Internet search engine, PubMed searching of MEDLINE requires a little investment of time. Using the MeSH database to define the subject of interest is one of the most useful ways to improve the quality of a search. Using MeSH terms in conjunction with limits (such as publication date or publication type), qualifiers (such as adverse effects or prevention and control), and text-word searching is another. Finding one article on the subject and clicking on the "Related Articles" link to get a collection of similarly classified articles can expand a search that otherwise yields few results.

For lay users who are trying to learn about health and medicine topics, the NIH offers MedlinePlus; thus, although such users are still free to search and read the medical literature themselves (via PubMed), they also have some help with curating it into something comprehensible and practically applicable for patients and family members.

See also

Related Research Articles

National Center for Biotechnology Information Database branch of the US National Library of Medicine

The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. The NCBI is located in Bethesda, Maryland and was founded in 1988 through legislation sponsored by Senator Claude Pepper.

United States National Library of Medicine Worlds largest medical library

The United States National Library of Medicine (NLM), operated by the United States federal government, is the world's largest medical library.

PubMed is a free search engine accessing primarily the MEDLINE database of references and abstracts on life sciences and biomedical topics. The United States National Library of Medicine (NLM) at the National Institutes of Health maintain the database as part of the Entrez system of information retrieval.

Entrez Cross-database search engine for health sciences

The Entrez Global Query Cross-Database Search System is a federated search engine, or web portal that allows users to search many discrete health sciences databases at the National Center for Biotechnology Information (NCBI) website. The NCBI is a part of the National Library of Medicine (NLM), which is itself a department of the National Institutes of Health (NIH), which in turn is a part of the United States Department of Health and Human Services. The name "Entrez" was chosen to reflect the spirit of welcoming the public to search the content available from the NLM.

MedlinePlus is an online information service produced by the United States National Library of Medicine. The service provides curated consumer health information in English and Spanish with select content in additional languages. The site brings together information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), other U.S. government agencies, and health-related organizations. There is also a site optimized for display on mobile devices, in both English and Spanish. In 2015, about 400 million people from around the world used MedlinePlus. The service is funded by the NLM and is free to users.

Medical Subject Headings Comprehensive controlled vocabulary for the purpose of indexing journal articles and books in the life sciences

Medical Subject Headings (MeSH) is a comprehensive controlled vocabulary for the purpose of indexing journal articles and books in the life sciences. It serves as a thesaurus that facilitates searching. Created and updated by the United States National Library of Medicine (NLM), it is used by the MEDLINE/PubMed article database and by NLM's catalog of book holdings. MeSH is also used by registry to classify which diseases are studied by trials registered in ClinicalTrials.

A health or medical library is designed to assist physicians, health professionals, students, patients, consumers, medical researchers, and information specialists in finding health and scientific information to improve, update, assess, or evaluate health care. Medical libraries are typically found in hospitals, medical schools, private industry, and in medical or health associations. A typical health or medical library has access to MEDLINE, a range of electronic resources, print and digital journal collections, and print reference books. The influence of open access (OA) and free searching via Google and PubMed has a major impact on the way medical libraries operate.

PubMed Central (PMC) is a free digital repository that archives open access full-text scholarly articles that have been published in biomedical and life sciences journals. As one of the major research databases developed by the National Center for Biotechnology Information (NCBI), PubMed Central is more than a document repository. Submissions to PMC are indexed and formatted for enhanced metadata, medical ontology, and unique identifiers which enrich the XML structured data for each article. Content within PMC can be linked to other NCBI databases and accessed via Entrez search and retrieval systems, further enhancing the public's ability to discover, read and build upon its biomedical knowledge.

A bibliographic database is a database of bibliographic records, an organized digital collection of references to published literature, including journal and newspaper articles, conference proceedings, reports, government and legal publications, patents, books, etc. In contrast to library catalogue entries, a large proportion of the bibliographic records in bibliographic databases describe articles, conference papers, etc., rather than complete monographs, and they generally contain very rich subject descriptions in the form of keywords, subject classification terms, or abstracts.

The Vancouver system, also known as Vancouver reference style or the author–number system, is a citation style that uses numbers within the text that refer to numbered entries in the reference list. It is popular in the physical sciences and is one of two referencing systems normally used in medicine, the other being the author–date, or "Harvard", system. Vancouver style is used by MEDLINE and PubMed.

Index Medicus (IM) is a curated subset of MEDLINE, which is a bibliographic database of life science and biomedical science information, principally scientific journal articles. From 1879 to 2004, Index Medicus was a comprehensive bibliographic index of such articles in the form of a print index or its onscreen equivalent. Medical history experts have said of Index Medicus that it is “America's greatest contribution to medical knowledge.”

Medical literature retrieval or medical document retrieval is an activity that uses professional methods for medical research papers retrieval, report and other data to improve medicine research and practice.

The National Centre for Text Mining (NaCTeM) is a publicly funded text mining (TM) centre. It was established to provide support, advice, and information on TM technologies and to disseminate information from the larger TM community, while also providing tailored services and tools in response to the requirements of the United Kingdom academic community.

Embase is a biomedical and pharmacological bibliographic database of published literature designed to support information managers and pharmacovigilance in complying with the regulatory requirements of a licensed drug. Embase, produced by Elsevier, contains over 32 million records from over 8,500 currently published journals from 1947 to the present. Through its international coverage, daily updates, and drug indexing with EMTREE, Embase enables tracking and retrieval of drug information in the published literature. Each record is fully indexed and Articles in Press are available for some records and In Process are available for all records, ahead of full indexing. Embase's international coverage expands across biomedical journals from 95 countries and is available through a number of database vendors.

SafetyLit is a bibliographic database and online update of recently published scholarly research of relevance to those interested in the broad field of injury prevention and safety promotion. Initiated in 1995, SafetyLit is a project of the SafetyLit Foundation in cooperation with the San Diego State University College of Health & Human Services and the World Health Organization - Department of Violence and Injury Prevention.

POPLINE was a reproductive health database, containing citations with abstracts to scientific articles, reports, books, and unpublished reports in the field of population, family planning, and reproductive health issues. POPLINE was maintained by the K4Health Project at the Johns Hopkins Bloomberg School of Public Health/ Center for Communication Programs, and it was funded by the United States Agency for International Development (USAID).

DeCS – Health Sciences Descriptors is a structured and trilingual thesaurus created by BIREME – Latin American and Caribbean Center on Health Sciences Information – in 1986 for indexing scientific journal articles, books, proceedings of congresses, technical reports and other types of materials, as well as for searching and recovering scientific information in LILACS, MEDLINE and other databases. In the VHL, Virtual Health Library, DeCS is the tool that permits the navigation between records and sources of information through controlled concepts and organized in Portuguese, Spanish and English.

Anne O'Tate is a free, web-based application that analyses sets of records identified on PubMed, the bibliographic database of articles from over 5,500 biomedical journals worldwide. While PubMed has its own wide range of search options to identify sets of records relevant to a researchers query it lacks the ability to analyse these sets of records further, a process for which the terms text mining and drill down have been used. Anne O'Tate is able to perform such analysis and can process sets of up to 25,000 PubMed records.

<i>Citing Medicine</i>

Citing Medicine: The NLM Style Guide for Authors, Editors, and Publishers is the style guide of the United States National Library of Medicine (NLM). Its main focus is citation style and bibliographic style. The citation style of Citing Medicine is the current incarnation of the Vancouver system, per the References > Style and Format section of the ICMJE Recommendations. Citing Medicine style is the style used by MEDLINE and PubMed.

The Literatura Latino-Americana e do Caribe em Ciências da Saúde,, acronym LILACS, and previously called Latin American Index Medicus, is an on-line bibliographic database in medicine and health sciences, maintained by the Latin American and Caribbean Center on Health Sciences Information (also known as BIREME, located in São Paulo, Brazil. Similar to MEDLINE, which was developed by the United States National Library of Medicine, it contains bibliographic references to papers that have been published in a set of scientific and medical journals of the region, and that are not covered by MEDLINE.


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