PubMed Help

Publication Details

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Image pubmedhelp-Image001.jpg Tutorials

PubMed comprises over 30 million citations for biomedical literature from MEDLINE, life science journals, and online books. PubMed citations and abstracts include the fields of biomedicine and health, covering portions of the life sciences, behavioral sciences, chemical sciences, and bioengineering. PubMed also provides access to additional relevant web sites and links to the other NCBI molecular biology resources.

PubMed is a free resource that is developed and maintained by the National Center for Biotechnology Information (NCBI), at the U.S. National Library of Medicine (NLM), located at the National Institutes of Health (NIH).

Publishers of journals can submit their citations to NCBI and then provide access to the full-text of articles at journal web sites using LinkOut.

For a brief overview of searching PubMed, see the Quick Start section.


PubMed Quick Start

Section Contents

How do I search PubMed? Image pubmedhelp-Image002.jpg


Identify the key concepts for your search.


Enter the terms (or key concepts) in the search box.


Suggestions will display as you type your search terms. Click Turn off to temporarily disable the autocomplete feature. The autocomplete feature is based on PubMed query log analysis described in “Finding Query Suggestions for PubMed.”


Click Search. Click here to run this search in PubMed.

How do I search by author? Image pubmedhelp-Image002.jpg

Enter the author’s last name plus initials without punctuation in the search box, and then click Search. Names entered using either the lastname+initials format (e.g., smith ja) or the full name format (john a smith) and no search tag are searched as authors as well as collaborators if they exist in PubMed.

Click Advanced to use the search builder, and then select Author from the All Fields menu. The author search box includes an autocomplete feature.

If you only know the author’s last name, use the author search field tag [au], e.g., brody[au].

If an author name includes only stopwords, use the author search field tag [au] to search in combination with other terms, e.g., just by[au] seizure.




For additional information on author names in PubMed, please see the journal article, “Author Name Disambiguation for PubMed.”

How do I search by journal name?

Enter the journal name or abbreviation in the search box.

Click Advanced to use the search builder, and then select Journal from the All Fields menu.The journal search box includes an autocomplete feature.

How do I find a specific citation? I have some information such as the author, journal name and the year the article was published.

Enter the information in the search box and the PubMed citation sensor will automatically analyze the search for citation information.

Alternatively, use the Single Citation Matcher to find citations with a fill-in-the-blank format:


Click Single Citation Matcher from the PubMed homepage.


Enter the information you have in the fill-in-the-blank boxes.


Click Go.

Is there anything special for clinical searches?

From the Clinical Queries page you can search by a clinical study category, find systematic reviews and run medical genetics searches.

Clinical study category

The clinical study categories use built-in search filters that will limit retrieval to citations to articles reporting research conducted with specific methodologies, including those that report applied clinical research. To find citations for a specific clinical study category:


Click Clinical Queries from the PubMed homepage or from the advanced search more resources menu.


Enter your search terms in the search box, and then click search.


You may then change the category or scope, if desired.

How do I find systematic reviews or medical genetic searches?

Systematic Reviews is available on result sets as a filter under article types, as well as a selection on the Clinical Queries page.


Click Clinical Queries from the PubMed homepage or from the advanced search more resources menu


Enter search terms in the search box, and then click Search.


For medical genetics, change the search topic, if desired.

Can you explain the search results?

PubMed search results are displayed in a summary format, see the anatomy of search results page below.

Citations are initially displayed 20 items per page with the most recently entered citations displayed first.

You can mouseover a journal’s title abbreviation to display the full journal name.

Anatomy of the Summary Results

Image pubmedhelp-Image003.jpg

How do I display an abstract?

Click the title of the article to see the abstract. “No abstract available” is indicated on citations without an abstract.

How can I get a copy of the article?

Image pubmedhelp-Image001.jpg Tutorial

PubMed search results do not include the full text of the journal article. However, the abstract display of PubMed citations may provide links to the full text from other sources, such as directly from a publisher’s web site.

The full text journal site may require a subscription although access may be available through your local medical library. In addition, online journals sometimes provide free access. Consider visiting your local medical library if there is not an online copy available.

For more information on obtaining the article, see How to Get the Journal Article.

How can I save my results?

There are several ways to save PubMed search results including using the Clipboard to save citations temporarily and My NCBI Collections to save indefinitely.


Click the check box to the left of the citations you want to save.


From Send to, select Clipboard.


To display the items in the clipboard, click the Clipboard items link.

For additional information see Saving Citations Temporarily using the Clipboard.

For other save options, see:

I retrieved too many citations. How can I focus my search?

Image pubmedhelp-Image001.jpg Tutorial

To limit the number of search results:

  • Replace general search terms with more specific ones (e.g., search for low back pain instead of back pain).
  • Add additional terms to your search.
  • Use the sidebar filters to restrict your results by publication dates, species, article types, etc.
  • Click manage filters in the Filter your results portlet to change your My NCBI filter selections.

I retrieved too few citations. How can I expand my search?

  • Click the Similar Articles See all link for a relevant citation to display a pre-calculated set of PubMed citations closely related to the article.
  • Remove extraneous or specific terms from the search box.
  • Try using alternative terms to describe the concepts you are searching.

I’m not finding what I need. How does a PubMed search work?

PubMed may modify your search terms to enhance your retrieval.

To see how PubMed modified your search, consult the ‘Search details’ box displayed on the results page and click the “See more…” link for further information.

For additional information, see How PubMed works: Automatic Term Mapping.

I need further assistance and training

Contacting customer support

  • E-mail the PubMed Help Desk
  • Call the NLM Customer service desk: 1-888-FIND-NLM (1-888-346-3656)

Search Field Descriptions and Tags

Affiliation [AD]

Affiliation may be included for authors, corporate authors and investigators, e.g., cleveland [ad] AND clinic [ad], if submitted by the publisher. Multiple affiliations were added to citations starting from 2014, previously only the first author’s affiliation was included. The Abstract format displays affiliation for citations with fewer than 100 authors. PubMed includes the note “Contributed equally” in the affiliation field if this information is supplied by publishers.

Article Identifier [AID]

Includes article identifiers submitted by journal publishers such as doi (digital object identifier). These data are typically used for generating LinkOut links.

All Fields [ALL]

Untagged terms and terms tagged with [all fields] are processed using Automatic Term Mapping. Terms that do not map are searched in all search fields except for Place of Publication, Transliterated Title, Create Date, Completion Date, Entrez Date, MeSH Date, and Modification Date. Terms enclosed in double quotes or truncated will be searched in all fields and not processed using automatic term mapping. PubMed ignores stopwords.

Author [AU]

The format to search for this field is: last name followed by a space and up to the first two initials followed by a space and a suffix abbreviation, if applicable, all without periods or a comma after the last name (e.g., fauci as or o'brien jc jr). Initials and suffixes may be omitted when searching.

PubMed automatically truncates a search for an author's name to account for varying initials, e.g., o'brien j [au] will retrieve o'brien ja, o'brien jb, o'brien jc jr, as well as o'brien j. To turn off automatic truncation, enclose the author's name in double quotes and tag with [au] in brackets, e.g., "o'brien j" [au] to retrieve just o'brien j.

Searching by full author name for articles published from 2002 forward is also possible, if available. Full names display in the FAU field on the MEDLINE display format. Various limits on the number of authors included in the MEDLINE citation have existed over the years (see NLM policy on author names).




Author Identifier [auid]

The author identifier includes a unique identifier associated with an author, corporate or investigator name, if supplied by a publisher. The field includes the organization authority that established the unique identifier, such as, ORCID, ISNI, VIAF, e.g., orcid 0000-0001-5027-4446 [auid].

Book [book]

The book search field includes book citations, e.g., genereviews [book].

Use the following untagged searches to retrieve all book or book chapters, e.g., ataxia AND pmcbookchapter

books and chapters: pmcbook

books: pmcbooktitle

book chapters: pmcbookchapter

Comment Correction Type

The data in these fields are citations to other associated journal publications, e.g., comments or errata. Often these link to the respective citation. Comments/Corrections data can be retrieved by the search term that follows each type:

  • Comment in: hascommentin
  • Comment on: hascommenton
  • Corrected and republished in: hascorrectedrepublishedin
  • Corrected and republished from: hascorrectedrepublishedfrom
  • Dataset use reported in: hasassociatedpublication
  • Dataset described in: hasassociateddataset
  • Erratum in: haserratumin
  • Erratum for: haserratumfor
  • Expression of concern in: hasexpressionofconcernin
  • Expression of concern for: hasexpressionofconcernfor
  • Original Report in: hasoriginalreportin
  • Republished in: hasrepublishedin
  • Republished from: hasrepublishedfrom
  • Retracted and republished in: hasretractedandrepublishedin
  • Retracted and republished from: hasretractedandrepublishedfrom
  • Retraction in: hasretractionin
  • Retraction of: hasretractionof
  • Summary for patients in: hassummaryforpatientsin
  • Update in: hasupdatein
  • Update of: hasupdateof

Conflict of Interest Statement [COIS]

The conflict of interest statement from the published article. To retrieve all citations that contain conflict of interest statements, use the query hascois.

Corporate Author [CN]

Corporate author identifies the corporate or collective authorship of an article. Corporate names display exactly as they appear in the journal.

Note: Citations indexed pre-2000 and some citations indexed in 2000-2001 retain corporate authors at the end of the title field. For comprehensive searches, consider including terms and/or words searched in the title field [ti].

Create Date [CRDT]

The date the citation record was first created. Create Date is not included in All Fields retrieval; the [crdt] search tag is required.

Completion Date [DCOM]

The date NLM completed processing the citation. Completon Date is not included in All Fields retrieval; the [dcom] search tag is required.

Editor [ED]

The editor search field includes the editors for book or chapter citations.

EC/RN Number [RN]

EC/RN numbers are assigned by:

  • The Food and Drug Administration (FDA) Substance Registration System for Unique Ingredient Identifiers (UNIIs), e.g., Y92OUS2H9B
  • The Enzyme Commission (EC) to designate a particular enzyme, e.g., EC
  • The Chemical Abstracts Service (CAS) for Registry Numbers, e.g., 2751-14-6

The EC/RN number search field includes both the Registry Number and the Related Registry Number (available in the NLM MeSH Browser).

Entrez Date [EDAT]

Date the citation was added to the PubMed database. Exceptions: As of December 15, 2008, citations added to PubMed more than twelve months after the date of publication have the EDAT set to the date of publication, except for book citations. Prior to this, the Entrez Date was set to the Publication Date on citations published before September 1997. Entrez Date is not included in All Fields retrieval; the [edat] search tag is required.

Search results are displayed in Entrez Date order, i.e., last in, first out.

To search for a date range, insert a colon (:) between each date, e.g., 1996:1997 [edat] or 1998/01:1998/04 [edat].

Note: The Entrez Date is not changed to reflect the date a publisher supplied record is elevated to in process or when an in process record is elevated to indexed for MEDLINE.

See Searching By Date for additional information.

Filter [FILTER] [SB]

Technical tags used by LinkOut, filters include:

  • loall[sb] - citations with LinkOut links in PubMed
  • free full text[sb] - citations that include a link to a free full-text article
  • full text[sb] - citations that include a link to a full-text article

First Author Name [1AU]

The first personal author name in a citation.

Full Author Name [FAU]

The full author name for articles published from 2002 forward, if available. Full author searches can be entered in natural or inverted order, e.g., julia s wong or wong julia s.

Full Investigator or Collaborator Name [FIR]

The index for the article's full investigator or collaborator name, if available. Full investigator searching can be searched in natural or inverted order, e.g., harry janes or janes harry.

Grant Number [GR]

The grant number search field includes research grant numbers, contract numbers, or both that designate financial support by agencies of the US PHS (Public Health Service), and other national or international funding sources. The four parts of the grant data are:


number, e.g., LM05545


PHS 2-character grant abbreviation, e.g., LM


institute acronym, e.g., NLM NIH HHS


country, e.g., United States

Each individual grant part can be searched using [gr], e.g., NIH[gr]

See Grant codes and agency abbreviations used in grant numbers for the 2-character abbreviations, PHS agency acronyms, and other US and non-US funding organization.

More information about grant numbers:

  • NIH grant numbers, e.g., 5R01CA101211-03, typically have three main parts:
    • A prefix that indicates the type of grant, e.g., 5R01
    • An 8-character serial number consisting of a 2-character grant abbreviation and a 6-digit number, e.g., CA101211
    • A suffix with additional data such as grant year, e.g, 03
  • To search for an individual NIH grant number use the 8-character serial number and [gr] tag, e.g., ca101211[gr].
  • Grant numbers display in PubMed as they appear in the published article. If the grant number in the journal article is not 6 digits, e.g., CA84141, search by inserting a leading zero, e.g., ca084141[gr], so the entire string is a total of 8 characters long.
  • For a broader search, use the PHS 2-character grant abbreviation, e.g., ca[gr] or the institute acronym, e.g., nci[gr].
  • Search non-PHS organization names in full or individual parts, e.g., wellcome trust[gr], wellcome[gr].
  • For generic numbers, it may be necessary to include the organization or country, e.g., 193588[gr] AND canada[gr].


The ISBN for book or book chapters.

Issue [IP]

The number of the journal issue in which the article was published.

Investigator [IR]

Names of principal investigator(s) or collaborators who contributed to the research. Search names following the author field format, e.g., soller b [ir]

Journal [TA]

The journal search field includes the journal title abbreviation, full journal title, or ISSN number (e.g., J Biol Chem, Journal of Biological Chemistry, 0021-9258). If a journal title contains special characters, e.g., parentheses, brackets, enter the name without these characters, e.g., enter J Hand Surg [Am] as J Hand Surg Am.

Language [LA]

The language search field includes the language in which the article was published. Note that many non-English articles have English language abstracts. You may search using either the language or the first three characters of most languages, e.g., chi [la] retrieves the same results as chinese [la]. The most notable exception is jpn [la] for Japanese.

Last Author Name [LASTAU]

The last personal author name in a citation.

Location ID [LID]

Location ID includes the DOI or publisher ID that serves the role of pagination to locate an online article.

MeSH Date [MHDA]

The date the citation was indexed with MeSH Terms and elevated to MEDLINE for citations with an Entrez Date after March 4, 2000. The MeSH Date is initially set to the Entrez Date when the citation is added to PubMed. If the MeSH Date and Entrez Date on a citation are the same, and the Entrez Date is after March 4, 2000, the citation has not yet been indexed. MeSH Date is not included in All Fields retrieval; the [mhda] search tag is required.

Dates must be entered using the format YYYY/MM/DD [mhda], e.g. 2000/03/15 [mhda]. The month and day are optional (e.g., 2000 [mhda] or 2000/03 [mhda]).

To enter a date range, insert a colon (:) between each date, e.g., 1999:2000 [mhda] or 2000/03:2000/04 [mhda].

MeSH Major Topic [MAJR]

A MeSH term that is one of the main topics discussed in the article denoted by an asterisk on the MeSH term or MeSH/Subheading combination, e.g., Cytokines/physiology* See MeSH Terms [MH] below.

MeSH Subheadings [SH]

MeSH Subheadings are used with MeSH terms to help describe more completely a particular aspect of a subject. For example, the drug therapy of asthma is displayed as asthma/drug therapy; see MeSH/Subheading Combinations in MeSH Terms [MH] below.

The MeSH Subheading field allows users to "free float" Subheadings, e.g., hypertension [mh] AND toxicity [sh].

MeSH Subheadings automatically include the more specific Subheading terms under the term in a search. To turn off this automatic feature, use the search syntax [sh:noexp], e.g., therapy [sh:noexp].

In addition, you can enter the two-letter MeSH Subheading abbreviations rather than spelling out the Subheading, e.g., dh [sh] = diet therapy [sh].



MeSH Subheadings

MeSH Terms [MH]

The NLM Medical Subject Headings controlled vocabulary of biomedical terms that is used to describe the subject of each journal article in MEDLINE. MeSH contains approximately 26 thousand terms and is updated annually to reflect changes in medicine and medical terminology. MeSH terms are arranged hierarchically by subject categories with more specific terms arranged beneath broader terms. PubMed allows you to view this hierarchy and select terms for searching in the MeSH Database.

Skilled subject analysts examine journal articles and assign to each the most specific MeSH terms applicable - typically ten to twelve. Applying the MeSH vocabulary ensures that articles are uniformly indexed by subject, whatever the author's words.

Notes on MeSH Terms and Major MeSH Topic search fields:

  • To search the term only as a MeSH term, it must be tagged using the search field, e.g., [mh] for MeSH Terms or [majr] for MeSH Major Topic. A tagged term is checked against the MeSH translation table, and then mapped to the appropriate MeSH term(s). To turn off mapping to multiple MeSH terms, enter the tagged MeSH term in double quotes.
  • MeSH terms are arranged hierarchically by subject categories with more specific terms arranged beneath broader terms. MeSH terms in PubMed automatically include the more specific MeSH terms in a search. To turn off this automatic feature, use the search syntax [mh:noexp], e.g., neoplasms [mh:noexp].For more detailed information about MeSH vocabulary including the hierarchical structure, please see the MeSH homepage.
  • MeSH/Subheading Combinations: To directly attach MeSH Subheadings, use the format MeSH Term/Subheading, e.g., neoplasms/diet therapy. You may also use the two-letter MeSH Subheading abbreviations, e.g., neoplasms/dh. The [mh] tag is not required, however [majr] may be used, e.g., plants/genetics[majr]. Only one Subheading may be directly attached to a MeSH term. For a MeSH/Subheading combination, PubMed always includes the more specific terms arranged beneath broader terms for the MeSH term and also includes the more specific terms arranged beneath broader Subheadings. The broader Subheading, or one of its indentions, will be directly attached to the MeSH term or one of its indentions’. For example, hypertension/therapy also retrieves hypertension/diet therapy; hypertension/drug therapy; hypertension, malignant/therapy; hypertension, malignant/drug therapy, and so on, as well as hypertension/therapy.
  • To turn off the automatic inclusion of the more specific terms, use the syntax [field:noexp], e.g., hypertension [mh:noexp], or hypertension [majr:noexp], or hypertension/therapy [mh:noexp]. The latter example turns off the more specific terms in both parts, searching for only the one Subheading therapy attached directly to only the one MeSH term hypertension.
  • If parentheses are embedded in a MeSH term, replace the parentheses with a space and tag with [mh] e.g., enter the MeSH term Benzo(a)pyrene as benzo a pyrene [mh].
  • MeSH terms can be selected for searching in the MeSH database and from the advanced search builder index.

Modification Date [LR]

Modification date is a completed citation’s most recent revision date. Modification Date is not included in All Fields retrieval; the [lr] search tag is required.

NLM Unique ID [JID]

The NLM ID is the alpha-numeric identifier for the cited journal that was assigned by the NLM Integrated Library System LocatorPlus, e.g., 0375267 [jid].

Other Term [OT]

The author keyword field (OT field) is searchable with the text word [tw] and other term [ot] search tags. To retrieve all citations that have keywords, use the query haskeyword. Other term data may display an asterisk to indicate a major concept; however, you cannot search other terms with a major concept tag.


The owner search field includes the acronym that identifies the organization that supplied the citation data. Search using owner + the owner acronym, e.g. ownernasa.

Pagination [PG]

Enter only the first page number that the article appears on. The citation will display the full pagination of the article but this field is searchable using only the first page number.

Personal Name as Subject [PS]

Use this search field tag to limit retrieval to where the name is the subject of the article, e.g., varmus h[ps]. Search for personal names as subject using the author field format, e.g., varmus h[ps].

Pharmacological Action [PA]

Substances known to have a particular pharmacologic action. Each pharmacologic action term index is created with the drug/substance terms known to have that effect. This includes both MeSH terms and terms for Supplementary Concept Records.

Place of Publication [PL]

Indicates the cited journal's country of publication. Geographic place of publication regions are not searchable. In order to retrieve records for all countries in a region (e.g., North America) it is necessary to OR together the countries of interest. Note: This field is not included in all fields or text word retrieval.


Search for PMC or NIH manuscript identifiers using the appropriate prefix followed by the ID number, e.g., PMC2600426. To retrieve all NIH manuscript citations, use the query hasnihmsid.


To search for a PubMed Identifier (PMID), enter the ID with or without the search field tag [pmid]. You can search for several PMIDs by entering each number in the search box separated by a space (e.g., 17170002 16381840); PubMed will or the PMIDs together.

To search in combination with other terms, you must enter the search field tag, e.g., lipman[au] 16381840[pmid].

PMIDs do not change over time or during processing and are never reused.

Publication Date [DP]

Publication date is the date that the article was published.

Dates or date ranges must be searched using the format yyyy/mm/dd [dp], e.g. 1998/03/06 [dp]. The month and day are optional (e.g., 1998 [dp] or 1998/03 [dp]).

To enter a date range search, insert a colon (:) between each date, e.g., 1996:1998 [dp] or 1998/01:1998/04 [dp].

Use the following format to search X days, months or years immediately preceding today’s date where X = numeric value:

  • “last X days”[dp]
  • “last X months”[dp]
  • “last X year”[dp]


  • Journals vary in the way the publication date appears on an issue. Some journals include just the year, whereas others include the year plus month or year plus month plus day. And, some journals use the year and season (e.g., Winter 1997). The publication date in the citation is recorded as it appears in the journal.
  • Publication dates without a month are set to January, multiple months (e.g., Oct-Dec) are set to the first month, and dates without a day are set to the first day of the month. Dates with a season are set as: winter = January, spring = April, summer = July and fall = October.
  • If an article is published electronically and in print on different dates both dates are searchable and may be included on the citation prefaced with an Epub or Print label. The electronic date will not be searchable if it is later than the print date, except when range searching.
  • To search for electronic dates only use the search tag [EPDAT], for print dates only tag with [PPDAT].
  • Most journals now publish articles online on a continuous basis, as soon as they are ready for publication (after peer review and editing, etc.) instead of, or in addition to, publishing collections of articles as an “issue” on a periodic basis. When a journal deposits a citation for an “online first” article in PubMed, NLM appends the note “[Epub ahead of print]” to the online publication date. The citation is updated, and the ahead of print notation removed, when the article is included in a journal issue. The lag between the “online first” and “issue” publication dates may be days, weeks, months, or more than a year. In many cases, depending on the journal, the online first version is considered to be the version of record. The “[Epub ahead of print]” note in PubMed should not be taken to mean that the cited article is not the version of record.
  • Bookshelf citation publication dates are generated from the book’s publication date.

Publication Type [PT]

Describes the type of material the article represents (e.g., Review, Clinical Trial, Retracted Publication, Letter); see the PubMed Publication Types, e.g., review[pt]. Publication Types are arranged hierarchically with more specific terms arranged beneath broader terms. Publication types automatically include the more specific publication types in a search. To turn off this automatic feature, use the search syntax [pt:noexp], e.g., review [pt:noexp].



Publication Types

Publisher [PUBN]

Includes publisher names for Bookshelf citations.

Secondary Source ID [SI]

The SI field identifies secondary source databanks and accession numbers, e.g., GenBank, GEO, PubChem,, ISRCTN. The field is composed of the source followed by a slash followed by an accession number and can be searched with one or both components, e.g., genbank [si], AF001892 [si], genbank/AF001892 [si]. To retrieve all citations with an SI value, search hasdatabanklist.

The SI field and the NCBI sequence database links are not linked. The PubMed links to these databases are created from the reference field of the GenBank or GenPept flat file. These references include citations that discuss the specific sequence presented in these flat files.

Subset [SB]

The subset field is a method of restricting retrieval by subject, citation status and journal category, with the search tag [SB]. See also filters and Finding Related Links for a Citation Using LinkOut.

Supplementary Concept [NM]

Includes chemical, protocol, disease or organism terms. Synonyms to the supplementary concepts will automatically map when tagged with [nm]. This field was implemented in mid-1980; however, many chemical names are searchable as MeSH terms before that date.

Text Words [TW]

Includes all words and numbers in the title, abstract, other abstract, MeSH terms, MeSH Subheadings, Publication Types, Substance Names, Personal Name as Subject, Corporate Author, Secondary Source, Comment/Correction Notes, and Other Terms (see Other Term [OT] above) typically non-MeSH subject terms (keywords), including NASA Space Flight Mission, assigned by an organization other than NLM.

Title [TI]

Words and numbers included in the title of a citation, as well as the collection title for book citations.

Title/Abstract [TIAB]

Words and numbers included in a citation's title, collection title, abstract, other abstract and keywords. English language abstracts are taken directly from the published article. If an article does not have a published abstract, NLM does not create one.

Transliterated Title [TT]

Words and numbers in title originally published in a non-English language, in that language. Non-Roman alphabet language titles are transliterated. Transliterated title is not included in All Fields or Text Word retrieval so you must search terms using the [tt] search tag.


The PMID of a versioned citation is persistent. To retrieve previous versions use the format PMID.version, e.g., 20029666.4. The abstract display includes an “Other versions” link that lists the previous versions and corresponding publication date. Only the most recent version of a citation will be indexed, therefore the content, e.g., author names, abstract terms, from previous versions will not be retrieved for PubMed searches. Search ispreviousversion to retrieve all previous versions of citations.

Volume [VI]

The number of the journal volume in which an article is published.

Searching PubMed

Section Contents

Searching by author Image pubmedhelp-Image002.jpg

Enter the author’s name in the format of last name followed by initials. Omit punctuation.

More information about author searching:

  • Click Advanced and use the builder. Select Author from the All Fields menu and enter an author’s name. The author search box includes an autocomplete feature.
  • Author names are automatically truncated to account for varying initials and designations such as Jr. To turn off the truncation, use double quotes around the author's name with the author search field tag [au], e.g., "smith j" [au].
  • If only the author's last name is entered, tag the name with the author search field [au], to find the name in the author field only.
  • Use the [1au] tag to search for the first personal author or [lastau] to search for the last personal author name in a citation.
  • You may click an author link on the abstract display to execute a search for the author in PubMed. Results will display using a ranking algorithm if the author name is computationally similar for additional PubMed citations.

Full author names may be searched for citations published from 2002 forward if the full author name is available in the article. Enter a full author name in natural or inverted order, e.g., julia s wong or wong julia s.

More information about full author searching:

  • A comma following the last name for searching is optional. For some names, however, it is necessary to distinguish which name is the last name by using the comma following the last name, e.g., james, ryan.
  • Omit periods after initials and put all suffixes at the end, e.g., vollmer charles jr
  • Initials and suffixes are not required, if you include a middle initial or suffix, you will only retrieve citations for articles that were published using the middle initial or suffix.
  • To distinguish author initials that may match a full author name use the [fau] search tag, e.g., peterson do[fau].

Searching by journal title Image pubmedhelp-Image002.jpg

Enter in the search box one of the following:

  • full journal title (e.g., molecular biology of the cell)
  • title abbreviation (e.g., mol biol cell)
  • ISSN number, a standardized international code (e.g., 1059-1524)

To find full journal names, use the NLM Catalog, or mouseover the citation journal abbreviation.


Click Journals in NCBI Databases on the PubMed homepage.


Enter the journal name and click Search.

More information about journal searching:

  • Click Advanced and use the Builder. Select Journal from the All Fields menu and enter a journal title. The journal search box includes an autocomplete feature.
  • Tag the journal title by using the search field [ta] to limit your search to only the journal, e.g., gene therapy[ta], scanning [ta].
  • Searching with the full journal title or abbreviation is recommended for complete retrieval of indexed items; older citations may not have an ISSN.
  • If a journal title or abbreviation includes a special character (e.g., parentheses, brackets, &), enter the title or abbreviation without the special characters. For example, to search by the journal abbreviation j hand surg [am], enter j hand surg am.
  • Searching for a journal will automatically map to the official journal title and the title associated with an alternative title, if one exists. To turn off this automatic mapping enter the journal in double quotes and tag with [ta], e.g., “science”[ta].

A list of journals included in PubMed is available by FTP.



Journal Lists

Searching by date


Click Advanced and use the Builder.


Select a date field from the All Fields menu, e.g., Date – Publication, and enter a single date or a date range in the fill-in-the-blank boxes. Month and day are optional. If you want to search for a date range up to the current date, do not edit the to ‘present’ date box.


Click Search.

Searching by a single date in the search box

Enter dates using the format yyyy/mm/dd [date field]. There is a selection of date fields to use:

  • Date of Publication [dp] - Date searching includes both print and electronic dates of publication. Searching for a single date does not include items when the electronic date of publication is after the print date.
  • Electronic Date of Publication (if applicable) [epdat]
  • Print Date of Publication (if applicable) [ppdat]
  • Entrez Date [edat] - The date the citation first entered PubMed.
  • MeSH Date [mhda] - The date the citation was indexed with MeSH terms.
  • Create Date [crdt] – The date the citation record was first created.

The month and day are optional.

Searching for a date range in the search box

Enter date ranges using a colon (:) between each date followed by a [date field].

Comprehensive searches for a full year should be entered as 2000:2000[dp] rather than 2000[dp] to retrieve citations with a different print and electronic year of publication.

Date range searching includes both print and electronic dates of publication.

Searching for a relative date range

Use the following format to search for a relative date range:

  • term="last X days"[Search Tag]
  • term="last X months"[Search Tag]
  • term="last X years"[Search Tag]

where X is the number of days, months or years immediately preceding today’s date and [Search Tag] is the date search tag: [dp], [edat] or [crdt].


Image pubmedhelp-Image001.jpg Tutorial

You can narrow your search results by article types, text availability, publication dates, species, languages, sex, subjects, journal categories, ages and search fields.


Run a search in PubMed.


To activate a sidebar filter, click the filter selection. A checkmark will appear next to the activated filters.


Subsequent searches will be filtered until the selected filters are cleared.


  • To add additional filter categories to the sidebar, click the “Show additional filters” link, select the additional categories, and then click Show. To activate the additional filters, click the filter selection.
  • When filters are selected a Filters activated message will display on the results page.
  • To turn off filters, click either the “Clear all” link to remove all the filters, the “clear” link next to a filter category to clear the selections within that category, or the individual filter.
  • Citations may be excluded for some filter selections because they have not yet completed the MEDLINE indexing process.
  • Users can also activate additional filters with My NCBI filters.

Article types

Select article types to narrow your results based on the type of material the article represents, such as: Clinical Trial and Review.

Click the “more …” link, to add additional article types, and then click Show. The complete list of MEDLINE publication types is available. Systematic review articles are produced using a search strategy.

This filter may exclude some citations that have not yet completed the MEDLINE indexing process.

Text availability

To filter your results to only citations that include a link to full text, a link to free full text, or an abstract, click the appropriate selections.

Alternatively, you may search for citations with links to full text, free full text or include an abstract using the values: full text[sb], free full text[sb], or 'hasabstract'. No search field tag is required for hasabstract. You may also search for all MEDLINE citations with a structured abstract with ‘hasstructuredabstract’.

Note: Most citations in PubMed to articles published before 1975 do not include abstracts.

Publication Dates

From the filter sidebar Publication dates category, click 5 years, 10 years, or enter a date in the custom range box to filter your results by publication date.


Species selections restrict your results to human or animal studies.

This filter may exclude some citations because they have not yet completed the MEDLINE indexing process.


To add languages to the sidebar, click the “Show additional filters” link, select Languages, and then click Show. Language selections restrict your search to articles written in the specific language.

Click the “more …” link, to add additional languages, and then click Show.


Sex restricts your search results to a specific sex for an animal or human study.

To add sex to the sidebar, click the “Show additional filters” link, select Sex, and then click Show.

This filter may some citations because they have not yet completed the MEDLINE indexing process.


Subject filters restrict retrieval to specific subjects.

To add subjects to the sidebar, click the “Show additional filters” link, select Subjects, and then click Show. Subject filters include:

  • AIDS
  • Bioethics
  • Cancer
  • Complementary Medicine
  • Dietary Supplements
  • History of Medicine
  • Systematic Reviews
  • Toxicology
  • Veterinary Science

Subjects use a specialized search strategy.

Subjects can also be searched using the respective search value of aids, bioethics, cancer, cam, dietsupp, history, space, systematic, tox or veterinary followed by the [sb] search tag. The Systematic reviews selection is included in the article types' category.

Journal categories & more subsets

To add journal categories to the sidebar, click the “Show additional filters” link, select Journal categories, and then click Show.

The Journal/Citation subsets restrict retrieval to specialized journals or articles on specialized topics in other journals. The table lists the journal subsets, along with the code used for searching. Some subsets are closed and are no longer being assigned to current data.



Journal/Citation Subsets

To search for a Journal/Citation subset, enter in the search box: jsubset?, where ? represents the subset code.

The Journal/Citation subset does not require a search tag.

PubMed Central Subset

To restrict retrieval to citations that have a free full-text article available in PubMed Central (PMC), search pubmed pmc[sb].

Use the PMID/PMCID/NIHMSID Converter to convert IDs for publications referenced in PubMed and PMC. To retrieve citations that include an NIHMS ID use the query, hasnihmsid.

Citation Status Subsets

The citation status indicates the processing stage of an article in the PubMed database (see PubMed Citation Status Subsets).



Status Subsets

The status tags are included in the XML and MEDLINE displays. To search for a particular citation status, enter one of the search terms below followed by the [sb] search tag

  • publisher
  • inprocess
  • medline
  • oldmedline
  • pubmednotmedline

To search for the total number of PubMed citations, enter all [sb] in the search box.

Ahead of Print Citations

Publishers may submit citations for articles that appear on the web prior to their publication in final or print format. To search for these ahead-of-print citations, enter pubstatusaheadofprint.

Following publication of the completed issue, the date an article was published electronically is also displayed, e.g. Proc Natl Acad Sci U S A. 2003 Apr 1;100(7):3925-9. Epub 2003 Mar 24.


Age filters restrict results to a specific age group for a human study.

To add ages to the sidebar, click the “Show additional filters” link, select Ages, and then click Show.

Age filters include:

  • 80 and over: 80+ years
  • Adolescent: 13-18 years
  • Adult: 19+ years
  • Adult: 19-44 years
  • Aged: 65+ years
  • Child: 0-18 years
  • Child: 6-12 years
  • Infant: 1-23 months
  • Infant: birth-23 months
  • Middle Aged + Aged: 45+ years
  • Middle Aged: 45-64 years
  • Newborn: birth-1 month
  • Preschool Child: 2-5 years
  • Young Adult: 19-24 years

These filters may exclude some citations because they have not yet completed the MEDLINE indexing process.

Search Fields

Choose a search field to limit all terms entered in the search box to the selected field.

Click the “Show additional filters” link, select Search fields, and then click Show. Click the Choose... link under Search fields, select a search field, and then click Apply.

Understanding Your Search Results

Search results initially display in a summary format in the order they were entered in PubMed as last in, first out. You can change the display format.

A default of 20 citations is displayed per page. If there are more than 20 citations, they will be displayed on subsequent pages.

To display the abstract for a journal article, click the title for each citation. Citations that don’t include an abstract display the notation “No abstract available.”

PubMed may also include non-English abstracts, if supplied by the publisher. The additional language view links are available on the Abstract display. The abstract text defaults to English when a citation has an accompanying non-English abstract. To retrieve citations with non-English abstracts, use the query hasnonenglishabstract.

Anatomy of Summary Results

Image pubmedhelp-Image003.jpg

For additional information see: Displaying and Sorting Your Search Results

Displaying and Sorting Your Search Results

Section Contents

Modify your display settings for:

Use Send to for:

Use the results page controls to:

  • Move to another page

Changing the citation display format

Results are initially displayed in the Summary format, except a single citation result will display the abstract format. You can change the display for all or selected citations by selecting a format from the format menu.

To change the display format only for selected citations, click the check box to the left of each citation before selecting a display format.

See PubMed Citation Display Formats for a description of all the formats.



Display Formats

Changing the number of citations shown per page

From the per page menu displayed at the top of the results page, select the number of items per page to display. You can change the number of citations displayed on a single page from 5 to 200 items.

Sorting your search results

Select a sort by option. Sort options include: Most Recent, Best Match, Publication Date, First Author, Last Author, Journal, and Title.

More information about sorting:

  • A modified sort by selection will be active for subsequent searches until 8 hours of inactivity on the NCBI web site.
  • Citations in PubMed are displayed in reverse date added order: last in, first out. The most recent date is the date a record was initially added to PubMed, not the publication date. The secondary sort is PMID.
  • The retrieved by best match sort order for search results is based on an algorithm that analyzes each PubMed citation that includes the search terms. For each search query, "weight" is calculated for citations depending on how many search terms are found and in which fields they are found. In addition, recently-published articles are given a somewhat higher weight for sorting. The top articles returned by the weighted term frequency algorithm above are then re-ranked for better relevance by a new machine-learning algorithm. If any technical constraints prevent the machine-learning architecture from re-ranking the results, the sort will revert to the standard best match algorithm. Please see the NLM Technical Bulletin article for more information.
  • Publication dates without a month are set to January, multiple months (e.g., Oct-Dec) are set to the first month, and dates without a day are set to the first day of the month. Dates with a season are set as: winter = January, spring = April, summer = July and fall = October.
  • First author, last author and journal sort A to Z; the secondary sort is publication date. First author sorting incorporates all author names in a citation.
  • Results for related data, e.g., similar articles, display in ranked order and display the sort by option: Sorted by Link Ranking.
  • You may click an author link on the abstract display to execute a search for the author in PubMed. If an author name is computationally similar with an author name for additional PubMed citations, the results will display those citations first, in ranked order, followed by the non-similar citations. The results sort notation will display as, “Sort by: Author.” Author name disambiguation details are available in Liu W and Wilbur WJ.

Printing Search Results

Use the print function of your web browser.

To print citations from different searches, save the citations in PubMed’s Clipboard, and then print.

See also:

Move to another page of search results

The results display the number of citations retrieved and the number of pages necessary to display all the results. Use the per page menu to change the number of citations shown per page.

Click Next or Prev to move back or forward to adjacent pages and Last or First to display the first and last page of your results.

Displaying the Search Details

PubMed may modify or add additional search terms to your search to optimize retrieval.

See the results page Search details box to view your search as it was translated using automatic term mapping and search rules.

More information about Details:

  • The Query Translation box shows the search strategy used to run the search.
    • To edit the search in the Query Translation box, add or delete terms and then click Search.
    • Click URL to display the current search as a URL to bookmark for future use. Searches created using History numbers can not be saved using the URL feature.
  • The Result number link displays the total number of citations for the search.
  • Translations details how each term was translated using PubMed's search rules and syntax.
  • User Query shows the search terms as you entered them in the search box and any syntax errors with the query.
  • If your last action was displaying a similar article set or selected items in another format, Details will indicate this rather than the last query.

Saving and E-mailing Results and Searches

Section Contents

Saving citations temporarily using the Clipboard

The Clipboard provides a place to collect selected citations from one or several searches. The Clipboard will be lost after 8 hours of inactivity on PubMed or other NCBI databases.

You may also save your search results indefinitely using My NCBI Collections.

To add citations to the Clipboard:


In your search results, use the citation check boxes to select citations. To save all your citations do not click any check boxes.


Use Send to, and select Clipboard.


To view your selections, click the Clipboard portlet items link.

To delete citations from the Clipboard:

  • Use the Remove from clipboard link to delete individual items, or use the check boxes to select items to delete, and then click the Remove selected items link.
  • To delete all citations from the Clipboard, do not select any items, click the Remove all link.

More information about the Clipboard:

  • Citations in the clipboard display item in clipboard.
  • The clipboard portlet displays the total number of items in the clipboard. A link to the clipboard is also available under the homepage PubMed Tools.
  • The maximum number of items that can be sent to the clipboard is 500. If you select Clipboard from send to without selecting citations, PubMed will add all (up to 500 citations) of your search results to the clipboard.
  • The clipboard will not add a citation that is currently in the clipboard; it will not create duplicate entries.
  • Your web browser must be set to accept cookies to use the clipboard.
  • Citations in the clipboard are represented by the search number #0, which may be used in Boolean search statements. For example, to limit the citations you have collected in the Clipboard to English language articles, use the following search: #0 AND english [la]. This does not affect or replace the Clipboard contents.

Saving citations as a text file


In your search results, use the citation check boxes to select citations. You may move to other pages to continue your selections. If you do not make any selections, PubMed will save the entire retrieval.


From Send to, select File.


Your web browser will prompt you to save the PubMed search results in a file on your computer.

More information about saving citations to a file:

  • Saving a large retrieval may take several minutes.
  • The default for the send to file feature is to save the entire retrieval unless you select specific citations. For example, if you use send to file for results displaying 1 to 20 of 2,356, your saved file will contain all 2,356 citations.
  • Select format CSV to generate an abbreviated summary citation in a comma separated file.
  • To save citations in HTML format, use the Save as function of your browser. Change the file extension to html. When saving as HTML, only those citations displayed on the page will be saved; therefor, consider changing the number of items per page.

Exporting citations into citation management software

To export citations into a citation management software program such as EndNote, Mendeley or Citavi:


In your search results, use the citation check boxes to select citations. To export all the citations do not select any citations.


From Send to, select Citation manager.


Import this saved file into your citation management program.

Questions regarding commercial software packages should be directed to the respective companies.

E-mailing citations


In your search results, use the check boxes to select citations. To e-mail all citations displayed on the page, do not make any selections.


From Send to, select E-mail.


Choose selections for Format, Sort by Number to send, and start from citation.


Enter an e-mail address. You may also enter additional text that will be included in the e-mail.


Click E-mail. The system returns you to your results page and displays a confirmation e-mail sent message.

Note: Use My NCBI to create an automatic e-mail update for searches.

Your PubMed results will be sent from the NCBI automatic mail server, Sent by NCBI [], with a "Subject" of PubMed Search Results. Do not reply to this message. This is not a functioning customer service e-mail address.

More information about e-mailing citations:

  • You may e-mail up to 200 items at a time to a single e-mail address.
  • The search will be included in your results email, or a notation indicating the number of selected items.
  • The CAPTCHA image does not display for users that are signed in to My NCBI.

Saving searches as RSS (Really Simple Syndication) feeds

PubMed RSS feeds use the My NCBI “What’s New” strategy for updating searches; therefore, you will only retrieve new items for your search since the last time you were connected to your RSS reader.

To create an RSS search feed:


Run a search in PubMed.


Click RSS located below the Search box.


You may edit the feed name and limit the number of items displayed, and then click Create RSS. If the number of citations retrieved is greater than the number of items displayed the feed will include a link to display the complete PubMed retrieval.


Click the XML icon to display the XML and copy and paste the URL into the subscribe form in your RSS reader. Web browsers and RSS readers may use different options to copy the feed.

An RSS reader is required to use this service.

Creating a URL to bookmark your search

You can create a URL with your search terms that can be bookmarked in your web browser for future use, see creating a web link to PubMed.


Alternatively, run a search and then click See more in results page search details box.


Click URL below the Query Translation box.


Bookmark the URL using your web browser function. You can also copy the URL from the web browser’s URL address box.

More information about creating a bookmark:

  • Searches that were created using a search statement number in Advanced History (e.g., #1 OR #2 AND human[mh]) can not be saved using the URL feature because search will be lost when History expires.
  • After saving the bookmark, you may want to use your web browser's edit functions to rename the bookmark.


My NCBI saves searches, results, your bibliography, and features an option to automatically update and e-mail search results from your saved searches.

My NCBI preferences includes storing and changing your e-mail address, highlighting search terms, opening the abstract display supplemental data by default, and turning off the auto suggest feature.

Additional features include filtering search results, managing recent activity, and setting a LinkOut icon, document delivery services, and outside tool preferences.

Click the My NCBI Sign In link, located at the top right of the page header, to sign into My NCBI or register for an account.

How to Get the Journal Article

Image pubmedhelp-Image001.jpg Tutorial

PubMed does not include the full text of journal articles; however, click the icon in the top right corner of the abstract display to link to the full text, if available.

In addition, the abstract display may include a LinkOut – more resources link located at the bottom of the display, with additional full text sources.

Additional tips for obtaining articles.

Section Contents

  • Many articles are available for free.
  • If you are a physician, researcher, or health professional, utilize your affiliation with a medical library or institution.
  • If you are a member of the general public or not affiliated with a medical library or institution, try finding free copies, check with your local library, or go directly to the publisher.

Free copies of some articles may be obtained in these ways:

Free full text Filter

Use the filter sidebar and click the Free full text available link to narrow your results to resources that are available for free on the web.

PubMed Central

Click the Abstract display “Free in PMC” icon to link to the article in PubMed Central.

PubMed Central (PMC) is the U.S. National Institutes of Health (NIH) free digital archive of biomedical and life sciences journal literature.

Free from the publisher

Click the free full text icon on the abstract format. Some publishers will provide free access to articles after you register as a guest.

Note: When you click a full text icon or link in PubMed, you leave PubMed and are directed to the full text at an external provider's site. NCBI does not hold the copyright to this material, and cannot give permission for its use. Users should review all copyright restrictions set forth by the full text provider before reproducing, redistributing, or making commercial use of material accessed through LinkOut.

Please see the Copyright and Disclaimers page for additional information.

If you are affiliated with a hospital, university, or other institution

  • Your local medical library is your best option. If you see icons for your library on the abstract view this indicates that your library provides a link to the article or can direct you to an interlibrary loan service.

Example library icons:

Image pubmedhelp-Image004.jpg

Local library

Some local libraries have copies of medical journals or can get a copy of an article for you. Ask your local librarian about inter-library loan options and charges.

Direct from publisher

Journal publishers or related organizations may provide access to articles for a fee or may be free after registering as an individual or guest. When available, icons to these sources can be found on the Abstract format.

Additional links to articles may be available under LinkOut on the Abstract display.

Example abstract icons:

Image pubmedhelp-Image005.jpgImage pubmedhelp-Image006.jpgImage pubmedhelp-Image007.jpg

How to Download PubMed

Once a year, NLM releases a complete (baseline) set of PubMed citation records in XML format for download from our ftp servers. Incremental update files are released daily and include new, revised, and deleted citations. The PubMed DTD states any changes to the structure and allowed elements from year to year.

PubMed 2019 Baseline:

PubMed 2019 Update Files:

Terms and Conditions:

Documentation: 2019 PubMed XML Elements and Attributes

PubMed DTD:

Other Services Including the MeSH and NLM Catalog Databases

Section Contents

Searching by using the MeSH database

Searching for journal information in the NLM Catalog

Using PubMed Mobile

Creating a web link to search PubMed

Using the E-utilities programming tools

Using the Batch Citation Matcher

Using Batch Entrez

Searching by using the MeSH Database

Image pubmedhelp-Image001.jpg Tutorial

MeSH (Medical Subject Headings) is the NLM controlled vocabulary thesaurus used for indexing PubMed citations.

Use the MeSH database to find MeSH terms, including Subheadings, Publication Types, Supplementary Concepts and Pharmacological Actions, and then build a PubMed search. The MeSH database can be searched by MeSH term, MeSH Entry Term, Subheading, Publication Type, Supplementary Concept, or MeSH Scope Note.

More information about the MeSH database:

  • An autocomplete feature is available from the search box.
  • Search results are displayed in relevance-ranked order, therefore, when a user’s search exactly matches a MeSH Term, that Term is displayed first.
  • Click the MeSH term from the Summary display or choose Full from the display format menu to view additional information and search specifications, such as Subheadings, restrict to Major MeSH Topic, or exclude terms below the term in the MeSH hierarchy.
  • Year Introduced is the year the term was added to MeSH. If more than one year is shown, the term was available for indexing back to the earliest year noted. Articles are indexed using the vocabulary in place at the time of indexing, therefore, the year introduced for a term and the date of publication of a citation indexed with that term may not agree.

Launching PubMed searches from MeSH

To build a PubMed search from MeSH, run a search, select terms using the check boxes, and then click "Add to search builder" in the PubMed search builder portlet. You may continue searching and including additional terms to the PubMed search builder using the “Add to search builder” and Boolean pull-down menu. When you are finished, click “Search PubMed.”

Searching for journal information in the NLM Catalog

The NLM Catalog includes information about the journals in PubMed and the other NCBI databases.

Click Journals referenced in the NCBI Databases on the homepage of NLM Catalog or PubMed to limit your NLM Catalog results to the subset of journals that are referenced in NCBI database records.

See the NLM Catalog help for additional information.

Other journal resources include:

Using PubMed Mobile

PubMed Mobile provides a simplified mobile friendly web interface to access PubMed. PubMed Mobile includes the same search functionality and content as Standard PubMed, that is, all search terms and fields work similarly.

PubMed Mobile is also useful for users who require special adaptive equipment to access the web.

Using the E-utilities programming tools

E-utilities are tools that provide access to data outside of the regular NCBI web search interface. This may be helpful for retrieving search results for use in another environment. If you are interested in large-scale data mining on PubMed data, you may download the data for free from our ftp server. Please see the terms and conditions for data users.

Using the Batch Citation Matcher

Use the Batch Citation Matcher to retrieve PMIDs (PubMed IDs) for multiple citations in batch mode. The Matcher requires you enter the bibliographic information (journal, volume, page, etc.) in a specific citation format.

Using Batch Entrez

Use Batch Entrez to upload a file of PMIDs directly to PubMed.


Section Contents

How PubMed works: automatic term mapping

PubMed coverage

Consumer health

Error messages


Search field descriptions and tags

MeSH Subheadings

MeSH Subheading hierarchies

PubMed Publication Types


MEDLINE display format

NLM author indexing policy

Grant code and institute abbreviations used in grant numbers

PubMed character conversions

Clinical Queries Filters

Algorithm for finding best matching citations in PubMed

Computation of Similar Articles

PMID to PMC ID converter

Batch Citation Matcher Help

How PubMed works: automatic term mapping

Untagged terms that are entered in the search box are matched (in this order) against a MeSH (Medical Subject Headings) translation table, a Journals translation table, the Full Author translation table, Author index, the Full Investigator (Collaborator) translation table and an Investigator (Collaborator) index.

When a match is found for a term or phrase in a translation table the mapping process is complete and does not continue on to the next translation table.

1. MeSH translation table

The MeSH Translation Table contains:

  • MeSH terms
  • The See-Reference mappings (also known as entry terms) for MeSH terms
  • Pharmacologic action terms
  • Terms derived from the Unified Medical Language System (UMLS) that have equivalent synonyms or lexical variants in English
  • Supplementary concept (substance) names and their synonyms.

If a match is found in this translation table, the term will be searched as MeSH (that includes the MeSH term and any specific terms indented under that term in the MeSH hierarchy), and in all fields.

For example, if you enter child rearing in the search box, PubMed will translate this search to: "child rearing"[MeSH Terms] OR ("child"[All Fields] AND "rearing"[All Fields]) OR "child rearing"[All Fields]

If you enter a MeSH Term that is also a Pharmacologic Action PubMed will search the term as [MeSH Terms], [Pharmacologic Action], and [All Fields].

If you enter an entry term for a MeSH term the translation will also include an all fields search for the MeSH term associated with the entry term. For example, a search for odontalgia will translate to: "toothache"[MeSH Terms] OR "toothache"[All Fields] OR "odontalgia"[All Fields] because Odontalgia is an entry term for the MeSH term toothache.

Substance name mappings do not include a mapping for individual terms in a phrase, e.g., IL-22 will not include IL[All Fields AND 22[All Fields].

MeSH term mappings that include a standalone number or single character do not include a mapping for individual terms in a phrase, e.g., Protein C will not include Protein[All Fields] or C[All Fields].

More information about automatic term mapping:

  • See the results Search details to verify how your terms are translated. If you want to report a translation that does not seem accurate for your search topic, please e-mail the information to the NLM Help Desk.

2. Journals translation table

The Journals translation table contains the:

  • full journal title
  • title abbreviation
  • ISSN number.

These will automatically map to the journal abbreviation that is used to search journals in PubMed and in all fields. For example, a search for endocrine pathology will translate to: "Endocr Pathol"[Journal] OR ("endocrine"[All Fields] AND "pathology"[All Fields]) OR "endocrine pathology"[All Fields]

3. Full Author translation table

The full author translation table includes full author names for articles published from 2002 forward, if available. Enter a full author name in natural or inverted order, e.g., julia s wong or wong julia s.

More information about full author searching:

  • A comma following the last name for searching is optional. For some names, however, it is necessary to distinguish which name is the last name by using the comma following the last name, e.g., james, ryan.
  • Omit periods after initials and put all suffixes at the end, e.g., vollmer charles jr
  • Initials and suffixes are not required, if you include a middle initial or suffix, you will only retrieve citations for articles that were published using the middle initial or suffix.
  • To distinguish author initials that may match a full author name use the [fau] search tag, e.g., peterson do[fau].

4. Full Investigator (Collaborator) translation table

If the term is not found in the above tables, except for Full Author, and is not a single term, the full investigator table is consulted for a match. The full investigator (collaborator) translation table includes full names, if available. Enter a full investigator name in natural or inverted order, e.g., harry janes or janes harry.

5. Author index

If the term is not found in the above tables, except for Full Author or Full Investigator, and is not a single term, PubMed checks the author index for a match. PubMed automatically truncates a search for an author's name to account for varying initials, e.g., o'brien j retrieves o'brien ja, o'brien jb, o'brien jc jr, as well as o'brien j.

When combining multiple authors, to avoid a match with full author names, include initials or use the [au] search tag, e.g., ryan[au] james[au]. Author names comprised of only stopwords, e.g., as a, are not searched as authors if they are part of phrase, chemical burn as a danger, unless the search only includes the author name, e.g., as a.

6. Investigator (Collaborator) index

If the term is not found in the above tables, except for Full Author, Author, or Full Investigator, and is not a single term, PubMed checks the investigator index for a match.

7. If no match is found?

PubMed breaks apart the phrase and repeats the above automatic term mapping process until a match is found. PubMed ignores stopwords in searches.

If there is no match, the individual terms will be combined (ANDed) together and searched in all fields.

When a search includes terms that were tagged with a search field during the automatic term mapping process and retrieves zero results, the system triggers a subsequent search using “Schema: all .” “Schema: all” modifies the search by removing the automatically added search field tags, and then searches each term in all fields.

Consumer Health

The National Library of Medicine cannot provide specific medical advice. NLM urges you to consult a qualified health care professional for answers to your medical questions. NLM does not have pamphlets or other materials to mail.

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System Error Messages

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Typographical Errors

Please contact the journal publisher directly to report an error and initiate a correction to PubMed citations for content other than MeSH.

To report a MeSH error in a PubMed citation, please contact the NLM Help Desk and include the PMID number (e.g., PMID: 12345678), and an indication of the incorrect and correct information.

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PubMed Coverage

PubMed provides access to bibliographic information that includes MEDLINE, as well as:

  • The out-of-scope citations (e.g., articles on plate tectonics or astrophysics) from certain MEDLINE journals, primarily general science and chemistry journals, for which the life sciences articles are indexed for MEDLINE.
  • Citations that precede the date that a journal was selected for MEDLINE indexing.
  • Some additional life science journals that submit full text to PubMed Central and receive a qualitative review by NLM.
  • Citations for the NCBI Bookshelf collection.

For additional information, please see the NLM Fact Sheet: Medline, PubMed, and PMC (PubMed Central): How are they different?

MEDLINE is the NLM premier bibliographic database that contains references to journal articles in the life sciences with a concentration on biomedicine. MEDLINE records are indexed with NLM Medical Subject Headings (MeSH). The database contains citations from the late 1940s to the present, with some older material. New citations that have been indexed with MeSH terms, publication types, GenBank accession numbers, and other indexing data are available daily and display with the tag [Indexed for MEDLINE].

In Process Citations
PubMed's in-process records provide basic citation information and abstracts before the citations are indexed with NLM MeSH Terms and added to MEDLINE.

Publisher-Supplied Citations
Citations received electronically from publishers appear in PubMed daily. Most citations progress to in-process, and then to indexed for MEDLINE. However, not all citations will be indexed for MEDLINE. Publishers may submit citations for articles that appear on the web in advance of the journal issue's release. These ahead-of-print citations display the tag [Epub ahead of print].


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In the case of PubMed, it is information about your interactions that may be needed later to perform a function. Cookies placed by PubMed are removed from your computer after a set time period unless you choose to use a persistent cookie with the My NCBI automatic sign in function.

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  • Your computer's date and time settings are incorrect. Check your computer's time settings to ensure that they are correct.

MeSH Subheadings

See the MeSH Subheadings and scope notes and allowable categories on the NLM website.

MEDLINE display format

The MEDLINE Display Format tags table defines the data tags that compose the PubMed MEDLINE format. The tags are presented in alphabetical order. Some of the tags (e.g., CIN) are not mandatory and therefore will not be found in every PubMed MEDLINE format. Other tags (e.g., AU, MH, and RN) may occur multiple times in one record. This format is available for exporting citations into a citation management software program.

Not all fields are searchable in PubMed. See Search Field Descriptions and Tags.

NLM Author Indexing Policy

NLM author indexing policy is as follows:

  • 1966 - 1984: MEDLINE did not limit the number of authors.
  • 1984 - 1995: The NLM limited the number of authors to 10, with "et al" as the eleventh occurrence.
  • 1996 - 1999: The NLM increased the limit from 10 to 25. If there were more than 25 authors, the first 24 were listed, the last author was used as the 25th, and the twenty-sixth and beyond became "et al."
  • 2000 - Present: MEDLINE does not limit the number of authors.

More Information:

  • Beginning in mid-2005, the policy restrictions on number of author names in past years were lifted so that on an individual basis, a citation may be edited to include all author names in the published article, regardless of the limitation in effect when the citation was created.
  • Effective with 1992 date of publication, letters are indexed individually with authors rather than as an anonymous group.
  • Until 1990, NLM transliterated up to five authors' Cyrillic or Japanese names to the Roman alphabet.
  • Between 1990 and 2016, the first ten Cyrillic or Japanese names are transliterated. Chinese ideograms were not transliterated by NLM, but if transliterations of the authors names are available in the journal article or table of contents, they were included in the citation, even if that includes only one author in a multi-author article.
  • Beginning in 2016, author names are published in Roman characters in all MEDLINE journals, and NLM no longer transliterates Cyrillic or Japanese names. All author names are included as published.

PubMed Character Conversions

Certain characters have special meaning in searches, others are converted to spaces.

Searches that include the following characters are translated as follows:

parentheses ( ) - used to create Boolean nesting 
square brackets [ ] - search field tag qualification 
ampersand & - Boolean operator AND 
pipe | - Boolean operator OR 
forward slash / - MeSH/Subheading combinations 
comma , - typically forces a space, e.g., a,b is translated to a, b 
colon : - designates a range operation 
double quotes " - used to force a phrase search 
pound sign # - designates a History search statement when immediately followed by a number, e.g., #1 AND cat 
asterisk * - wildcard symbol for search term truncation, e.g., toxicol*

Characters converted to spaces in search queries:

exclamation mark !
pound sign #
dollar sign $ 
percentage sign % 
asterisk * 
plus symbol + 
minus symbol - 
period . 
semi-colon ; 
angle brackets < > 
equal sign = 
question mark ? 
backslash \ 
caret ^ 
underscore _ 
curly brackets { } 
approximately ~

Some characters are preserved during indexing to assist with the retrieval of substances, e.g., 1'-methyl

single quotes ‘

hypens -

Clinical Queries Filters

Medical Genetics Filters

Systematic Reviews Search Filter



Clinical Queries using Research Methodology Filters

The Clinical Queries search filters are based on the work of Haynes RB et al.



Medical Genetics Search Filters

The genetics searches were developed in conjunction with the staff of GeneReviews: Genetic Disease Online Reviews at GeneTests, University of Washington, Seattle.

Algorithm for finding best matching citations in PubMed

In the standard best match order, PubMed displays documents in order of decreasing relevance score. This score is calculated by comparing the input query to the document fields (e.g. Text, Author, Journal, etc.). Document fields are indexed to allow the system to quickly retrieve the documents matching a given query. During indexing, the terms (and their frequencies) in the document are calculated and stored for each index field. During retrieval, the term frequencies are used in a weighted fashion to return a ranked list of PubMed citations matching the terms in the user query. The relevancy of a document in a single term query is dependent on the following:

  • IDFt or the global weight of the term;
  • FWf or the weight of the field the term appears in;
  • FLf or the field length;
  • TFt or the local weight of the term.

IDFt – The global weight of a term assumes that terms are independent in their contribution to finding relevant material. If term t appears in nt documents and the total number of documents in the database is N, it will be given the global weight:


FWf – Since the contribution of a field to the overall representation of a document is not equal, fields have weights of their own, and consequently the occurrence of a term in a particular field will have more importance than in other fields. For example, in computing the weight of a document, the occurrence of a term in the title of a document would have more importance than the occurrence of the term in the abstract field. The actual values are optimized empirically and may change over time.

FLf – For every document, a field has a different length. The sum of all field lengths of a document is equal to the document length.

TFt – The local weight of a term measures its importance in a particular document for a specific field. It is the sum of weighted frequencies of the term for all fields of a document. Generally, the more frequent a term is within a document field, the more important it is in representing the content of that document as a whole.

TFt=f  fields|occurrences of t in f|FLf×FWf

Document scores

In a first pass, we generate document scores by using the local, global and field weights defined above. We calculate Okapi-BM25F [1], a field weighted version of Okapi-BM25 [2]:

dl=f  fieldsFLf×FWf ,
avdl~=average of dl across documents ,
scored,q= tqdTFtk11-b+bdlavdl~+TFt×IDFt ,

where b and k1 are free parameters, respectively set to 0.75 and 1.2 in PubMed.

Learned ranking

The top articles returned by the weighted term frequency algorithm above are then re-ranked for better relevance by a new machine-learning algorithm. (If any technical constraints prevent the machine-learning architecture from re-ranking the results, the sort will revert to the standard best match algorithm, described above.) The learned ranking algorithm combines over 150 signals that are helpful for finding best matching results. Most of these signals are computed from the query-document term pairs (e.g. number of term matches between the query and the document) while others are either specific to a document (e.g. publication type; publication year) or query (e.g. query length). The new ranking model was built on relevance data extracted from the anonymous and aggregated PubMed search logs over an extended period of time.

Formally, this training dataset contains a set of N PubMed queries Q= {q1, ,qN}, and for each query, a set of K documents D= {d1, ,dK} associated with their gold standard relevance scores L= l1,,lK are mined from our search logs. Each document dj is represented by a feature vector in R179 such that dj[v]R is the vth feature value of the document dj. In training, the goal is to find a function F: R179R that produces scores S={s1,,sK} such that when documents D are ordered by these scores, the resulting ranking is the closest to the optimal ordering of L. We use the LambdaMART framework [3] to learn pairwise preferences over document lists. This is done by optimizing an objective function based on a ranking metric, NDCG@T [4]:

DCG@T=t=1T2l(t)-1log2(t+1) ,

where IDCG@T is the ideal DCG@T, that is DCG@T for L. T is the truncation rank defining the list of documents that we score. For PubMed, we optimize NDCG at T=20. Say we are comparing two documents dj,dk with relevance labels lj>lk. The objective function is defined as:


where ojk=sj-sk and sj,sk are scores predicted by the function F of the system for these documents. An approximation of the derivative of the objective function is then used to identify whether documents should be swapped to maximize the NDCG@T score:

λjk=ΔNDCG@Tsj,sk×Ojkojk ,
Ojkojk=Ojksj=-11+eojk ,

A gradient is then calculated for each document dj by summing the gradients associated with all pairs of documents including dj:

λj=kdj,dk:lj lkλjk.

Training consists of hundreds of iterations, and for each of them, LambdaMART builds and stores a gradient boosted tree that guides reranking by promoting or demoting documents based on the direction provided by their λ-gradient. The resulting model is thus a forest of gradient boosted trees. The machine-learning based algorithm achieves significant improvement in retrieval performance over the previous weighted term frequency algorithm.

Robertson, Stephen, and Hugo Zaragoza. "The probabilistic relevance framework: BM25 and beyond." Foundations and Trends® in Information Retrieval 3.4 (2009): 333-389.
Robertson Stephen E., et al. Okapi at TREC-3. Nist Special Publication Sp. 1995;109:109.
Burges, Christopher JC. "From RankNet to LambdaRank to LambdaMART: An overview." Learning 11.23-581 (2010): 81.
Järvelin Kalervo, Kekäläinen Jaana. Cumulated gain-based evaluation of IR techniques. ACM Transactions on Information Systems. 2002;20(4):422–446. (TOIS)

Computation of Similar Articles

The neighbors of a document are those documents in the database that are the most similar to it. The similarity between documents is measured by the words they have in common, with some adjustment for document lengths. To carry out such a program, one must first define what a word is. For us, a word is basically an unbroken string of letters and numerals with at least one letter of the alphabet in it. Words end at hyphens, spaces, new lines, and punctuation. The 132 common, but uninformative, words (also known as stopwords) are eliminated from processing at this stage. Next, a limited amount of stemming of words is done, but no thesaurus is used in processing. Words from the abstract of a document are classified as text words. Words from titles are also classified as text words, but words from titles are added in a second time to give them a small advantage in the local weighting scheme. MeSH terms are placed in a third category, and a MeSH term with a subheading qualifier is entered twice, once without the qualifier and once with it. If a MeSH term is starred (indicating a major concept in a document), the star is ignored. These three categories of words (or phrases in the case of MeSH) comprise the representation of a document. No other fields, such as Author or Journal, enter into the calculations.

Having obtained the set of terms that represent each document, the next step is to recognize that not all words are of equal value. Each time a word is used, it is assigned a numerical weight. This numerical weight is based on information that the computer can obtain by automatic processing. Automatic processing is important because the number of different terms that have to be assigned weights is close to two million for this system. The weight or value of a term is dependent on three types of information: 1) the number of different documents in the database that contain the term; 2) the number of times the term occurs in a particular document; and 3) the number of term occurrences in the document. The first of these pieces of information is used to produce a number called the global weight of the term. The global weight is used in weighting the term throughout the database. The second and third pieces of information pertain only to a particular document and are used to produce a number called the local weight of the term in that specific document. When a word occurs in two documents, its weight is computed as the product of the global weight times the two local weights (one pertaining to each of the documents).

The global weight of a term is greater for the less frequent terms. This is reasonable because the presence of a term that occurred in most of the documents would really tell one very little about a document. On the other hand, a term that occurred in only 100 documents of one million would be very helpful in limiting the set of documents of interest. A word that occurred in only 10 documents is likely to be even more informative and will receive an even higher weight.

The local weight of a term is the measure of its importance in a particular document. Generally, the more frequent a term is within a document, the more important it is in representing the content of that document. However, this relationship is saturating, i.e., as the frequency continues to go up, the importance of the word increases less rapidly and finally comes to a finite limit. In addition, we do not want a longer document to be considered more important just because it is longer; therefore, a length correction is applied. This local weight computation is based on the Poisson distribution and the formula can be found in Lin J and Wilbur WJ.

The similarity between two documents is computed by adding up the weights (local wt1 × local wt2 × global wt) of all of the terms the two documents have in common. This provides an indication of how related two documents are. The resultant score is an example of a vector score. Vector scoring was originated by Gerard Salton and has a long history in text retrieval. The interested reader is referred to Salton, Automatic Text Processing, Reading, MA: Addison-Wesley, 1989 for further information on this topic. Our approach differs from other approaches in the way we calculate the local weights for the individual terms. Once the similarity score of a document in relation to each of the other documents in the database has been computed, that document's neighbors are identified as the most similar (highest scoring) documents found. These closely related documents are pre-computed for each document in PubMed so that when you select Similar articles, the system has only to retrieve this list. This enables a fast response time for such queries.

Batch Citation Matcher Help

To retrieve PubMed PMIDs or PubMed Central IDs:


Enter each citation string on a separate line below, or create a file using the following format:


Fields must be separated by a vertical bar with a final bar at the end of the string.

2. Enter your email address. Email messages may take several minutes to process and be sent to your email address.

3. If you created a file, click Browse to select it from your system directory.

If a match is not found the citation string will display one of the following:

  • INVALID_JOURNAL - The journal name is not a valid. See the journal lists or the NLM Catalog to find the correct journal abbreviation.
  • NOT_FOUND - The journal name is valid but the complete citation did not find a match.
  • AMBIGUOUS - The information provided matches more than one citation. Citation information with 3 or fewer matches include the PMIDs, and more than 3 matches include the total PMID match count. Use the Single Citation Matcher or ESearch to retrieve all citations for searched fields.


  • Select PMC from the database pull-down menu to change the default from PubMed.
  • Enter author names without punctuation as smith jc. Initials are optional.
  • Your key is any string you choose to tag the citation, it is returned unaltered.
  • The journal title field may include the full journal title or the title abbreviation.
  • Each citation field is searched starting with the journal title until a unique match is found.
  • The journal title is a required field however you may omit other fields. If you omit fields you must retain the vertical bars in the citation string. For example, if you omit the volume number 88 from the first example below it should be entered as:

proc natl acad sci u s a|1991||3248|mann bj|P32022-1|

Example input:

proc natl acad sci u s a|1991|88|3248|mann bj|P32022-1|

proc natl acad sci u s a|1992|89|3271|gould se|P26261-1|

proc natl acad sci u s a|1999|89|3271|gould se|P26261-1|

res microbiol|1992|143|467|ivey dm|P25966-1|

science|1987|235|182|palmenberg ac|P12296-2|

eschatology|1993|12|22|public jq|C12233-2|

virology|1993|193|492|hardy me|Q02945-1|

virus genes|1992|6|393||P27423-1|

yeast|1992|8|253|sasnauskas k|P24813-1|

Example output:

proc natl acad sci u s a|1991|88|3248|mann bj|P32022-1|2014248

proc natl acad sci u s a|1992|89|3271|gould se|P26261-1|1565618

proc natl acad sci u s a|1999|89|3271||P26261-1|NOT_FOUND

res microbiol|1992|143|467|ivey dm|P25966-1|1448623

science|1987|235|182|palmenberg ac|P12296-2|3026048


virology|1993|193|492|hardy me|Q02945-1|8382410

virus genes|1992|6|393||P27423-1|1335631

yeast|1992|8|253|sasnauskas k|P24813-1|1514324

Note: Tagged stopwords will not be ignored, e.g., among[ti], and will probably retrieve no results.