PubMed User Guide: Your Comprehensive Guide to Biomedical Literature Searching

Last update: January 14, 2025

Staying abreast of the latest biomedical research is crucial for healthcare professionals, researchers, students, and anyone involved in the life sciences. PubMed, a service of the National Library of Medicine (NLM), at the National Institutes of Health (NIH), stands as an indispensable tool in this endeavor. It provides free access to MEDLINE, citations for biomedical literature from life science journals, and online books. Whether you are conducting in-depth research, seeking clinical evidence, or simply exploring health-related topics, mastering PubMed is an invaluable skill.

This User Guide offers a comprehensive walkthrough of PubMed’s functionalities, from basic searching to advanced techniques, ensuring you can effectively navigate and utilize this powerful resource. We aim to enhance your search proficiency, enabling you to retrieve pertinent information efficiently and effectively. This guide will cover everything from crafting effective search queries and utilizing filters to managing your search results and leveraging PubMed’s advanced features.

For the latest updates and enhancements to PubMed, be sure to follow PubMed New and Noteworthy.

Frequently Asked Questions (FAQs)

This section addresses some of the most common queries users have when starting with PubMed.

Getting Started with PubMed Search

PubMed’s search interface is designed to be user-friendly, allowing you to initiate your literature search with ease.

How to Conduct a Basic PubMed Search

Searching PubMed starts with identifying the core concepts of your research question. Here’s a step-by-step guide to perform a basic search:

1. Identify Key Concepts: Break down your research question into its most important concepts or keywords. For example, if you’re interested in the effects of exercise on depression, your key concepts are “exercise” and “depression.”
2. Enter Search Terms: Type these key concepts into the PubMed search box located on the homepage.
3. Initiate Search: Press the Enter key or click the Search button to execute your query.

PubMed is engineered to simplify the search process. You generally don’t need to employ complex tags or syntax for routine searches. PubMed’s intelligent system employs several features to optimize your search experience:

• Best Match Sorting: Utilizing a sophisticated machine learning algorithm, PubMed sorts search results by “Best Match,” positioning the most relevant citations at the top of your results page. This ensures that you see the most pertinent articles first.
• Autocomplete Suggestions: As you type your search terms, PubMed offers suggestions through an autocomplete feature. These suggestions are derived from an analysis of PubMed query logs, helping you refine your search terms and discover relevant phrases. For more details, you can refer to “Finding Query Suggestions for PubMed.”
• Spell Check Feature: PubMed includes a spell-checking function that suggests alternative spellings for terms that might contain misspellings. This helps to correct typographical errors and broaden your search to include correctly spelled variations of your intended terms.
• Citation Sensor: For searches that resemble citation searches—those including author names, journal titles, publication dates, and article titles—PubMed’s citation sensor displays suggested results. This feature is particularly useful when you are trying to locate a specific citation and have some of its details.

PubMed Search Box: An example of the PubMed search interface where users input their search queries to find biomedical literature.

Refining Broad Searches: Too Many Citations?

If your initial search returns an overwhelming number of citations, you can employ several strategies to narrow down your results and focus your search:

• Use Specific Terms: Replace general terms with more precise vocabulary. For instance, instead of “heart problems,” use “coronary artery disease.” Specificity is key to reducing irrelevant results.
• Add More Search Terms: Incorporate additional keywords to refine your query. For example, searching for “exercise for depression in elderly adults” is more targeted than just “exercise and depression.”
• Apply Sidebar Filters: PubMed’s sidebar filters are powerful tools for refining results. You can restrict citations by publication date, availability of full text, article type (like reviews or clinical trials), species (human or animal), language, and more. These filters are located on the left sidebar of the search results page.

PubMed Filters Sidebar: A visual representation of the filters available on the PubMed search results page, allowing users to narrow down their search by various criteria such as article type, publication date, and species.

Expanding Narrow Searches: Too Few Citations?

Conversely, if your search yields too few citations, consider these methods to broaden your search and uncover more relevant articles:

• Explore Similar Articles: On the abstract page of a relevant citation, look for the Similar Articles section. This feature provides a pre-calculated list of PubMed citations that are closely related to the article you are viewing. It’s an excellent way to discover articles you might have missed with your initial search terms.
• Remove Specific Terms: If you’ve used highly specific terms, try removing some of them to broaden your search scope. For example, if “exercise interventions for postpartum depression in first-time mothers” is too narrow, try “exercise for postpartum depression.”
• Use Alternative Terms: Brainstorm synonyms or related terms for your key concepts. For “depression,” you might also search for “mood disorder,” “clinical depression,” or “major depressive disorder.”

Finding a Specific Citation Quickly

Need to find a specific article and have citation details? PubMed makes it straightforward:

• Paste Article Title: The simplest method is to paste the article title directly into the search box.
• Enter Citation Details: Alternatively, enter known details such as the author’s name, journal title, and publication year. PubMed’s citation sensor is adept at analyzing these details to pinpoint the exact citation you’re looking for.

The citation sensor is equipped with a fuzzy matching algorithm, which means it can still find the best match even if your search query contains minor inaccuracies or incomplete information. Field tags or Boolean operators are not necessary for basic citation searching, making the process intuitive and efficient.

Searching by Author Effectively

To search for publications by a specific author, follow these guidelines:

• Last Name and Initials: Enter the author’s last name followed by their initials, without punctuation, in the search box (e.g., smith ja). Then, click Search.
• Author Search Tag [au]: If you only know the last name, use the author search field tag [au] after the name (e.g., brody[au]). This tag specifically directs PubMed to search within the author field.

PubMed is flexible with author name formats:

• Format Flexibility: Names can be entered as lastname+initials (e.g., smith ja) or as full names (john a smith). PubMed will interpret these as author searches.
• Full Name Searches: Enter the full author name in natural order (julia s wong) or inverted order (wong julia s).

Important considerations for author searches:

• Full Names and Publication Dates: Full author names were not consistently included in PubMed citations before 2002. Full name searches are most effective for articles published from 2002 onwards.
• Optional Comma: A comma after the last name is generally optional. However, for names where the last name might be ambiguous, using a comma can clarify your search (e.g., james, ryan).
• Initials and Suffixes: Omit periods after initials and place suffixes at the end (e.g., vollmer charles jr). Initials and suffixes are not mandatory, but including them refines your search to match only those citations that include the exact initials or suffixes you specify.

Advanced author searching tips:

• Advanced Search Builder: For more refined author searches, use the Advanced search builder. Select “Author” from the “All Fields” menu. The author search box includes an autocomplete feature to assist you.
• Author Links in Abstracts: Clicking on an author’s name in the abstract view will automatically execute a search for that author in PubMed.
• Stopwords in Author Names: If an author’s name consists only of stopwords, use the [au] tag in combination with other terms to ensure accurate searching (e.g., just by[au] seizure).
• Author Name Truncation: PubMed automatically truncates author names to account for variations in initials and suffixes like “Jr.” To disable truncation, use double quotes around the author’s name with the [au] tag (e.g., “smith j”[au]).
• First and Last Author Search: Use [1au] to search for the first author or [lastau] for the last author of a publication.

PubMed Advanced Search – Author Field: An illustration showing the Advanced Search interface in PubMed, specifically highlighting the “Author” field option in the “All Fields” dropdown menu, used for conducting targeted author searches.

For in-depth information on author name disambiguation in PubMed, refer to “Author Name Disambiguation for PubMed.”

Searching by Journal Title

To find articles published in a specific journal, PubMed offers several options:

• Full Journal Title: Enter the complete journal title (e.g., molecular biology of the cell).
• Journal Title Abbreviation: Use the abbreviated journal title (e.g., mol biol cell).
• ISSN: Search by the International Standard Serial Number (ISSN) (e.g., 1059-1524).

PubMed simplifies journal searching with these features:

• Advanced Search Builder: To search by journal using the search builder, navigate to Advanced search and select “Journal” from the “All Fields” menu. The journal search box also includes an autocomplete feature for easier journal selection.
• NLM Catalog for Full Journal Names: To find full journal names or verify abbreviations, use the NLM Catalog. You can access it via:
  1. Clicking “Journals in NCBI Databases” on the PubMed homepage.
  2. Entering the journal name and clicking “Search.”
• Journal Search Tag [ta]: Limit your search specifically to the journal field using the [ta] search tag (e.g., gene therapy[ta], scanning[ta]).

Important tips for journal searching:

• Full Title or Abbreviation Preferred: Searching with the full journal title or abbreviation is recommended for the most comprehensive results. Older citations might not include ISSNs.
• Special Characters in Journal Titles: If a journal title or abbreviation includes special characters (parentheses, brackets, &, etc.), omit these characters when searching. For example, search for “j hand surg am” instead of “j hand surg [am]”.
• Automatic Mapping: PubMed automatically maps journal searches to the official journal title and any associated alternative titles. To disable this automatic mapping and search for the exact title, enclose the journal title in double quotes and use the [ta] tag (e.g., “science”[ta]).

A comprehensive list of journals indexed in PubMed is available via FTP.

Searching by Date Range and Publication Date

PubMed offers several ways to filter and refine your search results by date, allowing you to focus on articles published within specific timeframes.

Using the Results Timeline

PubMed’s results timeline is a visual tool that allows you to dynamically adjust the date range for your search results.

• Adjust Date Range: Located at the top of the search results page, the timeline displays the distribution of publications over time. You can click and drag the sliders on this timeline to modify the publication date range directly.

Note on Timeline Dates: The Publication Date timeline counts all publication dates provided by the publisher, including both electronic and print dates. Since articles may have different electronic and print publication dates spanning across years, the total count of results displayed on the timeline might differ slightly from the overall search results count.

Using the Advanced Search Builder for Date Filtering

For more precise date range specification, the Advanced Search Builder provides detailed options:

1. Access Advanced Search: Click on Advanced search to go to the Advanced Search page.
2. Select Date Field: Use the “All Fields” menu and choose a date-related field, such as “Date – Publication.”
3. Enter Date Range: Input a single date or a date range in the provided boxes. Month and day are optional. To search up to the present date, leave the ‘Present’ date box unchanged.
4. Add to Query: Click “Add” to append the specified date range to your search query in the query box.
5. Execute Search: After finalizing your query with other terms, click “Search” (or “Add to History”) to run your date-filtered search.

Searching Dates Directly in the Search Box

You can also specify dates directly within the PubMed search box using specific formats and date field tags:

• Date Format: Use the format yyyy/mm/dd [date field]. Month and day are optional (yyyy or yyyy/mm are also acceptable).
• Boolean Operators: When combining dates with other search terms, use Boolean operators like AND to refine your search.

Examples of Single Date Searches:

To find articles about cancer published on June 1, 2020:

cancer AND 2020/06/01[dp]

Available Date Fields:

• Date of Publication [dp]: [dp] includes both print and electronic publication dates. Searching a single date with [dp] will not include articles where the electronic publication date is after the print date.
• Electronic Date of Publication [epdat]: [epdat] for the electronic publication date, if available.
• Print Date of Publication [ppdat]: [ppdat] for the print publication date, if available.
• Entry Date [edat]: [edat] is the date the citation was added to PubMed, often used for “Most Recent” sorting.
• MeSH Date [mhda]: [mhda] is the date when MeSH terms were assigned to the citation.
• Create Date [crdt]: [crdt] is the date the PubMed record was initially created.

Examples of Date Range Searches:

To find articles on heart disease published between January 1, 2019, and December 1, 2019:

heart disease AND 2019/01/01:2019/12/01[dp]

For comprehensive searches across a full year, use the format 2000:2000[dp] rather than just 2000[dp] to ensure you retrieve citations with both print and electronic publication dates within that year.

Relative Date Range Searching:

PubMed also allows you to search for articles published within a relative date range from the current date:

• term="last X days"[date field]
• term="last X months"[date field]
• term="last X years"[date field]

Replace X with the number of days, months, or years, and [date field] with [dp], [edat], or [crdt].

For example, to find articles on diabetes published in the last 6 months:

diabetes="last 6 months"[dp]

Note that relative date range searches for publication dates may include citations with publication dates in the future, if publishers have submitted records ahead of official publication.

Utilizing Filters to Refine Your Search

PubMed filters are essential tools for narrowing your search results based on various criteria, enhancing the precision and relevance of your retrieved citations. Filters are categorized by:

• Publication Date
• Text Availability
• Article Attribute
• Article Type
• Article Language
• Species
• Sex
• Age
• Other

Applying Filters:

1. Run Your Search: First, perform your initial search in PubMed.
2. Select Filters: On the search results sidebar, click on the filter you wish to apply. A checkmark will appear next to the selected filter, indicating it is active.
3. Filter Persistence: Once activated, the selected filters will automatically apply to all subsequent searches until you manually turn them off or clear your browser data.
4. Filter Status Indicator: A green “Filters applied” message will be displayed at the top of the results page, confirming that filters are currently active.

PubMed Filters Applied Message: A screenshot showing the green banner at the top of PubMed search results, indicating that filters are currently active and being applied to the search.

Accessing Additional Filters:

Besides the default filters visible on the sidebar, PubMed offers a broader range of filters within each category:

1. “See all … filters” Link: Click the “See all … filters” link located within a filter category on the sidebar.
2. Pop-up Menu: A pop-up menu will appear, listing all available filters for that category.
3. Filter Selection: Select the additional filters you want to apply.
   • To cancel selections, click “Cancel” or the “X” in the upper right corner of the pop-up to close and return to your search results.
4. Apply Filters: Click “Apply.” This will close the pop-up, apply your selected filters to your search, and display them on the sidebar along with the default filters. These filters will remain active for future searches until cleared or browser cookies are cleared.

Clearing Filters:

• Clear All Filters: To deactivate all currently applied filters, click the “Clear filters” link in the green “Filters applied” message or the “Clear all filters” button at the bottom of the sidebar.
• Clear Individual Filters: To turn off specific filters, simply click the active filter on the sidebar to deselect it.
• Reset Filter Display: To revert the sidebar filters back to the default list and clear any applied filters, click the “Reset filters display” button at the bottom of the sidebar.

Important Information About Filters:

• MeSH Term Dependency: Many filters in the “Additional Filters” section rely on MeSH terms assigned during MEDLINE indexing. This means that using these filters might exclude relevant citations that have not yet been indexed or do not include the specific MeSH terms.
• Filter Search Strategies: For each filter, there is an equivalent PubMed query. These are detailed in the Filter search strategies section, allowing you to replicate filter effects directly in your search queries.
• Custom Filters: You can create and activate additional filters using My Custom filters. Once set up, these custom filters appear at the top of your sidebar under “My Custom Filters” for easy access.

Publication Date Filters

To filter by Publication Date, PubMed offers quick options like “1 year,” “5 years,” “10 years,” or allows you to enter a custom date range. These filters consider both electronic and print publication dates to narrow results by the timeframe of publication.

Text Availability Filters

PubMed provides filters to refine your search based on the availability of full text:

• Full Text: Limits results to citations that include a link to the full text article, often from publishers’ websites or institutional subscriptions.
• Free Full Text: Restricts results to citations with links to free full text, including articles available in PubMed Central (PMC), Bookshelf, and freely accessible content on publishers’ websites.
• Abstract: Filters for citations that include abstracts.

Alternatively, you can use search tags to achieve the same results: full text[sb], free full text[sb], or 'hasabstract'. No search field tag is needed for hasabstract. To find citations with structured abstracts, use 'hasstructuredabstract'.

Note: A significant portion of citations for articles published before 1975 in PubMed do not include abstracts.

Article Attribute Filter

The “Associated Data” filter helps you find citations that are linked to secondary source databanks and accession numbers. These links connect to records in other NLM databases (like GenBank, ClinicalTrials.gov) or external repositories (such as figshare, Dryad) through NCBI’s LinkOut service. Data links are provided by publishers and data repositories participating in NCBI’s LinkOut.

Article Type Filters

Article type filters allow you to refine your search based on the nature or format of the article, such as “Clinical Trial” or “Review.” Article types are also known as publication types.

You can expand the list of article type filters on the sidebar by using the “See all article type filters” link. A comprehensive list of publication types in PubMed is available for reference.

Article type filters rely on the Publication Type [pt] data assigned to citations, except for the Systematic Review filter, which uses a combination of a search strategy and publication type.

Publication type data is provided by publishers or assigned during MEDLINE indexing, so these filters might exclude recently added citations that have not yet completed the MEDLINE indexing process.

Systematic Reviews Filter

To specifically search for systematic reviews in PubMed, use the “Systematic Review” article type filter on the sidebar. Alternatively, in the search box, append your search terms with AND systematic[sb]. For instance:

lyme disease AND systematic[sb]

The “Systematic Review” filter employs a specialized search strategy in conjunction with the “Systematic Review” publication type [pt]. To limit your search only to citations with the “Systematic Review” publication type, use systematic review[pt]. However, be aware that this may miss some relevant citations not yet fully indexed.

Article Language Filters

Language filters restrict your search to articles published in specific languages. You can add more language filters to the sidebar via the “See all article language filters” link.

PubMed, by default, displays English language titles and abstracts when provided by publishers. Check the abstract display for links to abstracts in other languages, if available. Language filters are located under the “Additional Filters” section.

Species Filters

Species filters allow you to limit your search to studies involving humans or animals:

• Humans
• Other Animals

These filters narrow results to citations indexed with associated MeSH terms for species during MEDLINE indexing. While generally precise, they might exclude some relevant results that lack these specific MeSH terms, such as preprints or articles in non-MEDLINE indexed journals. Species filters are found in the “Additional Filters” section.

Sex Filters

Sex filters refine your search to studies focused on a specific sex, either female or male, in human or animal studies:

• Female
• Male

Similar to species filters, sex filters rely on MeSH terms for sex assigned during MEDLINE indexing. They are typically accurate but might exclude some relevant citations lacking these MeSH terms, particularly those not indexed for MEDLINE. Sex filters are located under “Additional Filters.”

Age Filters

Age filters restrict results to specific age groups in human studies.

Age filters use MeSH terms for age groups assigned during MEDLINE indexing. They are generally precise but may exclude citations without these specific age-related MeSH terms. Age filters are also located under “Additional Filters,” with more options available via the “See all age filters” link.

Age filter categories include:

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

Other Filters & More Subsets

PubMed offers additional specialized filters and subsets under the “Additional Filters” section.

Exclude Preprints

The “Exclude preprints” filter removes preprint citations from your search results. Alternatively, you can manually exclude preprints by adding NOT preprint[pt] to the end of your search query. For more information on preprints in PubMed, see Preprints.

MEDLINE Subset

The “MEDLINE” filter limits results to citations indexed for MEDLINE. To use it in a query, add medline[sb] to your search.

PubMed Central Subset

To limit your search to citations with free full text articles in PubMed Central (PMC), search for "pubmed pmc"[sb]. Use the PMID/PMCID/NIHMSID Converter to convert IDs between PubMed and PMC. To find citations with an NIHMS ID, use the query hasnihmsid.

Citation Status Subsets

Citation status indicates the processing stage of an article in PubMed (see PubMed Citation Status Subsets). To search for a specific status, use terms followed by [sb]:

• publisher
• inprocess
• medline
• pubmednotmedline

To find the total number of PubMed citations, search all[sb].

Ahead of Print Citations

To find citations for articles published online before print, use pubstatusaheadofprint.

Advanced Search Techniques: Phrase Searching, Wildcards, and Boolean Operators

PubMed provides advanced techniques to refine your searches, including phrase searching, wildcards, and Boolean operators.

Searching for an Exact Phrase

PubMed’s Automatic Term Mapping (ATM) often recognizes phrases, especially common medical terms. For example, searching for “fever of unknown origin” is directly recognized as a MeSH Term.

To bypass ATM and search for an exact phrase, use these methods:

• Phrase Indexing: PubMed uses a phrase index for efficient phrase searching. To explore this index, use the “Show Index” feature in the Advanced Search builder. Select a field, enter the start of your phrase, and click “Show Index.”

• Quotation Marks: Enclose your phrase in double quotes. This tells PubMed to search for the exact phrase without automatic term mapping. For example, "health planning" will search for the MeSH term “Health Planning” but will not include more specific terms like “Health Care Rationing.”

• Proximity Search for Unindexed Phrases: If a phrase is not in the phrase index, use a proximity search with a distance of 0 to find the quoted terms immediately next to each other in any order. For example, to search for “cognitive impairment in multiple sclerosis” as an exact phrase:

  "cognitive impairment in multiple sclerosis"[tiab:~0]

PubMed regularly updates its phrase index based on frequency and relevance. To suggest a phrase for inclusion, contact the NLM Help Desk.

Wildcards and Truncation for Broadening Searches

Wildcards in PubMed use an asterisk * to represent zero or more characters within a term, allowing you to search for variations of words.

• Wildcard Usage: Use * to substitute for characters (e.g., vaccin* schedul* finds “vaccine schedule,” “vaccination schedules,” etc.).
• Minimum Characters: Terms must have at least 4 characters before the first wildcard (e.g., colo*).
• Multiple Wildcards: You can use multiple wildcards in a single term (e.g., organi*ation*).

Wildcards can also be used in phrase searches:

• Double Quotes: "breast feed*"
• Search Tag: breast feed*[tiab]
• Hyphen: breast-feed*

Phrases can include multiple wildcards: "colo* cancer*"

Important Note: Wildcards disable Automatic Term Mapping (ATM), preventing PubMed from including MeSH terms and related narrower terms in your search. For example, "heart attack*" will not map to “Myocardial Infarction.” However, wildcards are particularly useful for capturing variations of phrases, including different spellings and singular/plural forms. For example, "tumo*r associated macrophage*" retrieves both “tumor” and “tumour” variations.

Combining Search Terms with Boolean Operators (AND, OR, NOT)

Boolean operators allow you to combine search terms in PubMed to create more precise queries. Always use uppercase for Boolean operators:

• AND: Narrows your search to results that include all specified terms (default operator). Example: "vitamin c common cold" is interpreted as "vitamin c" AND "common cold".
• OR: Broadens your search to include results that contain at least one of the specified terms. Example: cancer OR neoplasm.
• NOT: Excludes results that contain a specific term. Example: allergies NOT rhinitis.

PubMed processes searches from left to right. Use parentheses to group concepts and control the order of operations. For example, (heart attack OR myocardial infarction) AND aspirin will first process the OR group, then combine the result with aspirin.

Note on ATM and Boolean Operators: PubMed’s ATM may parse phrases automatically. For example, “air bladder fistula” might be parsed as a phrase. To prevent this, use Boolean operators between each term: air AND bladder AND fistula.

Search Details in Advanced Search show how PubMed translated your search query.

Using Search Field Tags for Precision

Search field tags allow you to search for terms within specific fields of PubMed records, such as title, author, or affiliation. Add the tag in square brackets after your term (e.g., UCLA[ad] searches for “UCLA” in the affiliation field only).

Key points about search field tags:

• Format: Enclose tags in square brackets. Case and spacing are ignored (crabs[mh] = Crabs[mh]).
• ATM Bypass: Tags disable Automatic Term Mapping (ATM), limiting the search to the exact term in the specified field.
• Phrase Searching with Tags: Applying a tag after multiple terms attempts to search those terms as a phrase (kidney allograft[tiab]).
• Multiple Terms in Same Field: Tag each term individually to search multiple terms in the same field (covid-19[ti] vaccine[ti] children[ti]).
• Advanced Search Builder: Use the Advanced Search builder to easily construct complex searches using specific fields.

Search field tags provide a wide array of options for targeted searching.

Proximity Searching: Terms Within a Distance

Proximity searching helps you find terms that appear within a specified number of words of each other in the Title, Title/Abstract, or Affiliation fields.

Format for proximity searches:

"search terms"[field:~N]

Where N is the maximum number of words between terms, and [field] is [Title], [Title/Abstract], or [Affiliation].

Important aspects of proximity searching:

• Order Independent: Terms can appear in any order. For exact phrase order, use phrase searching.
• ATM Disabled: Automatic Term Mapping is not applied to quoted terms.
• Wildcard Incompatibility: Proximity searching does not work with wildcards. Wildcards in proximity searches are ignored.
• Boolean Combinations: Proximity searches can be combined with other terms using Boolean operators (e.g., "hip pain"[Title:~4] AND stretching).
• Stopwords and Booleans: Stopwords and Boolean operators within quoted terms are treated as regular keywords.

Examples of Proximity Searches:

1. “rationing healthcare” in Title within 2 words:

   "rationing healthcare"[Title:~2]

   This will find phrases like “rationing healthcare,” “healthcare rationing,” etc.

2. “patient physician relationship” in Title/Abstract adjacent to each other:

   "patient physician relationship"[Title/Abstract:~0]

   N=0 requires terms to be next to each other, in any order.

3. Combining proximity searches with Boolean operators:

   "accidental overdose"[Title/Abstract:~3] AND acetaminophen
   "patient physician relationship"[tiab:~0] OR “patient doctor relationship”[tiab:~0]

Displaying, Sorting, and Navigating Search Results

PubMed’s search results are designed for easy review and navigation.

Understanding Your Search Results Display

By default, PubMed displays 10 citations per page, sorted by “Best Match.” Results are shown in a summary format with snippets from the abstract, highlighting terms related to your query.

To view the abstract of a citation, click on its title.

Journal names are abbreviated in the summary view. Mouse over a journal abbreviation to see the full title in Abstract format.

Displaying an Abstract View

To see the full abstract of a citation:

• Click the Title: Click the title of the citation from the search results page to directly access its abstract page.
• Change Display Format: Alternatively, change the display format for all results to “Abstract” using the “Display options” button at the top right of the search results page.

PubMed includes non-English abstracts if provided by the publisher. English abstracts are shown by default, with links to view abstracts in other languages when available on the Abstract display. To specifically retrieve citations with non-English abstracts, use the query hasnonenglishabstract.

Changing the Display Format of Search Results

You can customize how search results are displayed using the “Display options” button:

1. Click “Display options”: Located in the upper right corner of the search results page.
2. Select Format: Choose your preferred format from the dropdown menu.
3. Apply Format: Results will refresh and display in your selected format.

Changing the format after selecting specific items will only apply the new format to the selected citations.

The default summary format includes abstract snippets. You can disable snippets in “Display options” by deselecting “Abstract snippets.”

Showing More Results Per Page

PubMed displays 10 results per page by default. To view more results per page:

1. Click “Display options”: At the top right of the results page.
2. Select Items per Page: Choose from options: 10, 20, 50, 100, or 200 items per page.
3. Apply Setting: Your selection will be saved for subsequent searches until browser cookies are cleared.

Click “Show more” at the bottom of the page to load the next set of results, or use “Jump to page” to navigate directly to a specific page number.

Sorting Your Search Results

PubMed’s default sort order is “Best Match.” You can change the sort order using the “Sort by” dropdown menu at the top of the search results page.

Your selected sort order will persist for future searches until browser cookies are cleared.

Available Sort Orders

• Best Match: Uses an algorithm to rank citations by relevance, considering term frequency, field matches, and publication recency. See Algorithm for finding best matching citations in PubMed for details.
• Most Recent: Sorts citations by reverse date added order, newest first. The date is when the record was added to PubMed, not publication date. Secondary sort is PMID.
• Publication Date: Sorts citations by reverse chronological order, newest to oldest, based on the earliest publication date (print or electronic). Dates without month default to January, months without day default to the first day. Seasons are mapped to months (Winter=January, Spring=April, Summer=July, Fall=October).
• First Author: Alphabetical sort by first author’s last name, secondary sort by PMID.
• Journal: Alphabetical sort by journal name, secondary sort by PMID.

Reverse Sort Order

For “Most Recent,” “Publication Date,” “First Author,” or “Journal” sorts, you can reverse the order (ascending/descending) by clicking the up/down arrow next to the sort option. Reverse sort is not available for “Best Match.”

Computed Author Sort

Clicking an author name link in the abstract view performs an author search. If computationally similar author names exist in PubMed, results will prioritize citations by those similar authors, ranked, followed by other citations. See Liu W and Wilbur WJ for author name disambiguation details.

Accessing Full Text Articles

PubMed primarily provides citations and abstracts, not full text articles. However, abstract views often include links to full text from various sources:

• Publisher’s Website: Links to the journal publisher’s site, which may require a subscription or payment.
• PubMed Central (PMC): Links to free full text articles in PMC.

Full text access can be obtained through:

Free Full Text Filter

On the filter sidebar, click “Free full text” to limit results to articles freely available on the web, including PMC, Bookshelf, and publishers’ free content. Alternatively, use free full text[Filter] in your query.

PubMed Central (PMC) Access

If full text is in PubMed Central (PMC), a “Free in PMC” icon appears in the abstract view under “Full Text Links.” Click this icon to view the article in PMC. PMC is NIH’s free digital archive of biomedical and life sciences literature.

Access from Publisher Websites

Publishers or related organizations may offer free or paid access to articles. Icons linking to these sources are in the “Full Text Links” and/or “LinkOut” sections of the abstract view. Icons often indicate free full text when available.

Note: Clicking full text links in PubMed directs you away from PubMed to external provider sites. NCBI does not hold copyright to this material and cannot grant permissions for its use. Review copyright restrictions on the provider’s site before reusing content. See Copyright and Disclaimers for more information.

Institutional Access

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

• Library Links: Check for library icons in the abstract view, indicating your library provides access, has journal subscriptions, or offers interlibrary loans.
• Local Medical Library: Your local medical library is the best resource. Librarians can assist with access, including interlibrary loans.

Local Library Resources

Local public libraries may also have medical journals or inter-library loan services. Consult your local librarian for options.

Figures in PubMed Abstracts

PubMed abstracts include figures if the full text article is available in PubMed Central (PMC). Click on the thumbnail image to view a larger version, the figure caption, and a link to copyright information in PMC. Figures are from the PMC archived article version, which may sometimes be the Author Manuscript version.

Finding Similar Articles

Abstract pages include a “Similar articles” section with links to related PubMed citations.

• “See all similar articles” Link: Retrieves a pre-calculated set of citations closely related to the viewed article.
• Ranked by Relevance: Similar articles are ordered from most to least relevant, with the “linked from” citation listed first.
• Algorithm: Similarity is calculated by comparing words from titles, abstracts, and MeSH terms using a word-weighted algorithm.
• Filters Not Applied: Filters are not active for similar articles lists.
• Refining Similar Articles: You can refine the list using your search History, where similar articles are represented as a list of PMIDs. Use this list in a new search query to further refine results. Note that refining may remove the ranked order and some highly relevant citations.

See Computation of similar articles for algorithm details.

Cited By Information

PubMed abstracts may include “Cited by” links to resources citing the current article. This data is provided by publishers and NCBI resources, when available, but may not be exhaustive.

References in Abstracts

PubMed abstracts include reference lists when available. References are provided for full text articles in PMC’s open access subset and for citations where publishers supply reference data.

Grants and Funding Information

PubMed displays grant numbers, contract numbers, and intramural research identifiers associated with publications, provided by:

1. Publishers during data submission to PubMed and PMC.
2. Authors, principal investigators, or project directors.
3. NLM text mining and indexing processes.

Funding information in PubMed is standardized to enhance discovery and impact monitoring. For example, variations of NIH grant numbers are normalized to a standard format like R01 GM987654. See Grants and funding [gr] for search details.

The scope of funding information in PubMed has expanded over time to support public access policies of NIH and other funding organizations. Since 1981, NLM has included funding information, initially limited to US Public Health Service (PHS) grants and contracts, and expanded since 2006 to include broader funding sources.

Reporting Funding Information Errors

If you find errors in funding information linked to a PubMed record, contact the NLM help desk. NLM will not remove funding associations reflecting the acknowledged funding in the article without a published correction to maintain the integrity of the scientific record.

Navigating Searches with Over 10,000 Results

PubMed can display up to 10,000 results. For searches exceeding this limit:

• Refine Your Search: Use more specific terms, filters, or advanced search techniques to narrow down your results.
• Analyze the First 10,000 Results: Typically, the most relevant articles are within the first few pages of results, especially when sorted by “Best Match.”

Discovering Related Data in NCBI Databases

Abstract pages may include links to related data in other NCBI databases under the “Related information” section. See Entrez Link Descriptions for a full list of database options.

MEDLINE indexed citations include extra information like MeSH terms and publication types with links to search these in PubMed and the MeSH Database.

To search across all NCBI databases simultaneously, use the NCBI Search page.

Finding Related Resources Using LinkOut

PubMed records often include LinkOut resources linking to external websites like publishers, libraries, and biological databases. LinkOut helps you find full text or related information, though access may require fees.

To view LinkOut resources, scroll to the “LinkOut” section at the end of an abstract page. To find citations with free full text links, use the “Free full text” filter. For citations with any full text links, use AND full text[sb] in your search.

More about LinkOut:

• LinkOut resource categories are selected by the providers.
• See the LinkOut providers list for current providers.
• Publisher icons in abstracts indicate electronic data provision to NCBI. Links are only available for LinkOut participants, who are responsible for link maintenance.

Reporting Broken or Problem Links

LinkOut links are managed by LinkOut providers. Report broken links or subscription inquiries directly to the provider, whose contact info is usually on their website.

Citing, Saving, and Sharing PubMed Citations

PubMed offers various tools to manage and share citations effectively.

Temporarily Saving Citations Using the Clipboard

The Clipboard is a temporary storage area to collect up to 500 citations from one or more searches. Items in the Clipboard are stored in browser cookies and are deleted after 8 hours of inactivity. For longer-term saving or access across devices, use Collections.

Adding to Clipboard:

1. Select Citations: Check the boxes next to citations in your search results. To save all results (up to 500), leave boxes unchecked.
2. Send to Clipboard: Use the “Send to” button and choose “Clipboard.”
3. Confirm Selection: If no citations were selected, a dropdown will appear with options to add selected, page results, or all results (up to 500).
4. Access Clipboard: Click the “Clipboard” link below the search bar (visible only when the Clipboard is not empty).

Deleting from Clipboard:

• Remove Individually: On the Clipboard page, click “Remove from Clipboard” under each item.
• Remove Selected Items: Select items using checkboxes and click “Remove selected items.”
• Remove All Items: Click “Remove all” to clear the entire Clipboard.

More about the Clipboard:

• “Item in Clipboard” message marks citations already saved.
• Maximum 500 items.
• No duplicate entries; adding a citation already in the Clipboard has no effect.
• Browser cookies must be enabled.
• Clipboard contents are represented by search number #0, usable in Boolean searches (e.g., #0 AND english [la]). This does not alter Clipboard content.

Saving Citations Indefinitely Using My NCBI Collections

Collections in My NCBI offer permanent storage for search results, with no limit on the number of collections. Collections can be made public for sharing.

Saving to a New Collection:

1. Sign In: Log into My NCBI.
2. Run Search: Perform your PubMed search.
3. Select Citations: Select citations using checkboxes or leave unchecked to save all (up to 1,000).
4. Send to Collections: Use “Send to” and choose “Collections.”
5. Create New Collection: Select “Create a new collection.”
6. Name Collection: Enter a unique, short title (under 100 characters).
7. Add to Collection: Click “Add.”

Adding to an Existing Collection:

1. Follow steps 1-4 above. “Add to an existing collection” is the default option.
2. Choose Collection: Use the dropdown menu to select an existing collection.
3. Add to Collection: Click “Add.”

For managing, sharing, and editing collections, see Collections in My NCBI Help.

Saving Citations as a Text File

Use the “Save” button to download citations to a text file.

1. Select Citations: Check boxes for citations from search results or Clipboard, or select “All results on this page” or “All results” from the “Save” menu.
2. Click Save: Choose “Selection” and “Format” from the menu.
   • “Selection”: Choose “Selection,” “All results on this page,” or “All results” (up to 10,000).
   • “Format”: Select “Summary (text),” “PubMed,” “PMID list,” “Abstract (text),” or “CSV.”
3. Create File: Click “Create file.”
4. Download File: Your browser will prompt you to save the file.

More on saving citations to a file:

• Saving large sets may take time.
• To save in HTML, use browser’s “Save as” function, changing extension to .html. Only citations on the current page will be saved in HTML; consider showing more results.

Citing an Article Using the Cite Button

The “Cite” button provides formatted citations for easy copying and pasting or downloading as an .nbib file for reference managers.

Clicking “Cite” for an item opens a pop-up with citations in AMA, MLA, APA, or NLM styles. You can copy the citation or download an .nbib file for import into reference management software.

Note: Always check capitalization and formatting for compliance with specific citation style guidelines, as automated citation tools may not always be fully accurate.

To export multiple citations, see instructions for saving citations as a text file using “Summary (text)” format for NLM style, or exporting to citation management software.

Exporting Citations to Citation Management Software

Use “Send to: Citation Manager” to export citations as an .nbib file compatible with many citation management programs.

1. Select Citations: Choose citations from search results or Clipboard, or select “All results on this page” or “All results” from “Send to: Citation Manager.”
2. Click “Send to”: Choose “Citation Manager.”
3. Confirm Export: Select “selection,” “page results,” or “all results” (up to 10,000).
4. Create File: Click “Create file.”
5. Download File: Your browser will prompt you to save the .nbib file.
6. Import to Software: Import the saved file into your citation management program.

You can also download .nbib files for individual citations using the “Cite” button. For questions about citation management software, contact the respective software companies.

Emailing Citations

1. Select Citations: Choose citations from search results or Clipboard, or email all citations on the page without selection.
2. Click “Email”: Click the “Email” button.
3. Enter Email Details: Enter the recipient’s email, select citations to send and format.
4. Send Email: Click “Send email.” A confirmation message will appear.

More on emailing citations:

• Emails are sent from NCBI automatic mail server ([email protected]). Do not reply to this address.
• CAPTCHA is not shown for users signed into My NCBI.

Creating an Email Alert for a Search

Click “Create alert” under the search bar to set up automatic email updates for your searches. You must be signed into My NCBI to use this feature. See Saving and Managing Searches for more information.

Creating an RSS Feed for a Search

Click “Create RSS” under the search box to create an RSS feed for your search.

1. Feed Name: The RSS feed name defaults to your search terms; edit as needed.
2. Select Items Displayed: Choose the number of items in the feed from the dropdown menu. You can manually edit limit= parameter in the RSS link to show up to 1000 items, but note increased loading time.
3. Create RSS Feed: Click “Create RSS button.”
4. Copy RSS Link: Click “Copy” to copy the RSS Feed Link.
5. Use with Feed Reader: Use this link in your RSS feed reader or application.

Printing Search Results

Use your web browser’s print function to print search results. To print citations from different searches, save them to PubMed’s Clipboard first, then print from the Clipboard.

Getting a Permalink to Bookmark or Share

To get a permanent link for an individual citation, use the permalink under “Share” on the abstract page.

For search results, copy the URL from your browser’s address bar or use your browser’s bookmark function.

To create a URL manually:

1. Base URL: https://pubmed.ncbi.nlm.nih.gov/?term=search
2. Replace “search”: Replace “search” with your query terms.
3. Escape Spaces: Convert spaces to plus signs (+), e.g., “Biochem Soc Trans” becomes Biochem+Soc+Trans.

Example: Search for “antioxidant and chocolate”:

https://pubmed.ncbi.nlm.nih.gov/?term=antioxidant+chocolate

Optional search parameters can be added to the URL, such as format=, sort=, sort_order=, and size=.

Example: Search for “breast cancer,” sorted by ascending publication date, 50 citations per page:

https://pubmed.ncbi.nlm.nih.gov/?term=breast+cancer&sort=pubdate&sort_order=asc&size=50

Important notes about PubMed links:

• Some settings rely on cookies and session data not included in URLs. Advanced History searches (e.g., #1 OR #2 AND human[mh]) cannot be saved via URL as History expires.
• For frequent queries or large data retrieval, use E-Utilities. Adhere to usage guidelines.
• NCBI’s Disclaimer and Copyright must be evident to users. Consult legal counsel for copyright compliance. NLM cannot advise on copyright issues.

Downloading PubMed Data

NLM releases a full baseline set of PubMed citation records in XML format annually for FTP download. Daily incremental update files are also available. See Download PubMed Data and the PubMed DTD for details. Binary mode must be used for downloads.

Advanced Search Features in PubMed

PubMed’s Advanced Search page offers tools for precise and complex literature searches.

Searching in a Specific Field Using the Advanced Search Builder

The Advanced Search Builder simplifies searching within specific fields like author or journal. Autocomplete is available for some fields.

1. Select Field: From the “All Fields” dropdown, choose the field you want to search.
2. Add Terms: Enter terms in the builder and click “Add to query.” The default operator is AND; change to OR or NOT if needed.
3. Execute Search: Once your query is built, click “Search” (or “Add to History”).

You can also search specific fields by manually adding search field tags to your terms, bypassing Automatic Term Mapping.

Browsing the Index of Terms

The “Show Index” feature in the Advanced Search Builder displays an alphabetical list of terms in selected PubMed search fields, helpful for exploring vocabulary, especially MeSH Terms.

1. Go to Advanced Search: Click “Advanced” to access the Advanced Search page and use the Builder.
2. Select Field: Choose a search field from “All Fields” menu. “Show Index” is available for compatible fields only.
3. Enter Term and Show Index: Type a term in the search box, then click “Show Index.”
4. Browse Index: An alphabetical list of terms and approximate citation counts appears.
5. Select Terms: Scroll to find terms, highlight, and add to the search box. Multiple terms can be selected.
6. Build Query: Add terms from the builder to construct your search query.
7. Run Search: Click “Search” (or “Add to History”).

More on using the index:

• Boolean operators are processed left to right.
• Builder automatically ORs multiple terms from the index and adds parentheses.
• A slash / appears after a space in MeSH terms. Enter MeSH terms followed by a slash to directly access MeSH/Subheading combinations.
• “Show Index” is not available for date fields.

Using Search History

PubMed keeps a history of your searches on the Advanced Search page under “History.” This requires browser cookies to be enabled.

History table columns:

• Search: Numbered chronologically. Search numbers (#1, #2, etc.) can be used in place of queries to combine searches (e.g., #1 OR #2). Repeated queries move to the top but keep their original number. History is limited to the last 100 searches; older searches are removed as new ones are added.
• Actions: “Add” puts the query in the query box. “Delete” removes from history. “Save” allows saving queries in My NCBI.
• Query: Shows the search string you entered.
• Details: Click “>” to expand and see how PubMed translated your search, including automatic term mapping.
• Results: Number of citations retrieved. Click the number to view results in PubMed.
• Time: Timestamp of search execution.
  • Download: Click “Download” to get a CSV file of current History items. Note that Excel may truncate long queries in CSV; text editors are recommended for full view.
• Delete: Click “Delete” to remove all queries from History. History expires after 8 hours of inactivity.

Previewing Search Result Counts

1. Go to Advanced Search: Click “Advanced” to reach the Advanced Search page.
2. Build Query: Use the builder or type your search in the query box.
3. Toggle Button to “Add to History”: Use the split button to change from “Search” to “Add to History.”
4. Add to History: Click “Add to History.” This runs the search without leaving the Advanced Search page.
5. View Result Count: See your query and result count in the History table.

Combining Searches Using History

Searches in your History can be combined for more complex queries.

1. Go to Advanced Search: Click “Advanced” to navigate to the Advanced Search page.
2. Add Query from History: In the History table, click the “More Actions” icon “…” next to your query.
3. Select “Add query”: Choose “Add query” to copy the query to the Query box.
4. Combine Queries: After adding a query, Boolean operators (AND, OR, NOT) will appear as options for adding more queries.
5. Edit Query (Optional): Modify the query in the Query box if needed.
6. Execute Search: Click “Search” (or “Add to History”).

More on combining searches:

• Search numbers (e.g., #1 OR #2) can replace search strings.
• Clipboard contents are represented by #0 and can be used in searches (e.g., #0 AND english [la]). This does not change Clipboard contents.

Viewing Search Details

PubMed’s “Search Details” in Advanced Search show how queries are translated, including automatic term mapping, term modifications, and any warnings.

1. Access Search Details: Go to the Advanced Search page under “History.”
2. Expand Details: Click the chevron icon “>” next to a query in History.
3. Review Translation: Expanded details show PubMed’s search strategy for that query.

More information on Search Details:

• “Translations” show term mappings using PubMed’s rules. Untranslated terms (like exact phrases) are not listed as ATM is bypassed.
• “Warnings” highlight potential errors in the original query in bold red, such as syntax errors or invalid tags. Warnings also appear in PubMed when the search runs or is added to History.

Other PubMed Services

PubMed provides additional specialized services beyond basic and advanced searching.

Clinical Queries for Focused Clinical Research

PubMed Clinical Queries offers specialized search interfaces for:

COVID-19 Article Search

COVID-19 article filters limit searches to citations about the 2019 novel coronavirus, categorized by research topic. See COVID-19 article filters for filter strategies, which may evolve.

Using COVID-19 article filters:

1. Go to Clinical Queries: Click “Clinical Queries” from the PubMed homepage.
2. Enter Search Terms: Input terms in the search box.
3. Click Search.
4. Select Category: Choose a category: “General,” “Mechanism,” “Transmission,” “Diagnosis,” “Treatment,” “Prevention,” “Case Report,” “Forecasting,” or “Long COVID.”
5. Preview Results: View results in the “COVID-19 Articles” column.
6. View All Results: Click “See all” link below the preview to view full results in PubMed.

To use COVID-19 filters in a query, add the filter name with [Filter] tag, e.g., LitCPrevention[Filter]. Available filters:

• LitCGeneral
• LitCMechanism
• LitCTransmission
• LitCDiagnosis
• LitCTreatment
• LitCPrevention
• LitCCaseReport
• LitCForecasting
• LitCLongCOVID

Example: Search for Remdesivir using the COVID-19 General filter:

Remdesivir AND LitCGeneral[Filter]

Clinical Study Category Search

Clinical Study Categories use built-in filters to find citations reporting research with specific methodologies, focusing on applied clinical research. See Clinical Study Categories filters for filter strategies.

Using Clinical Study Categories:

1. Go to Clinical Queries: Click “Clinical Queries” from the PubMed homepage.
2. Enter Search Terms.
3. Click Search.
4. Select Category: Choose from “Therapy,” “Diagnosis,” “Etiology,” “Prognosis,” or “Clinical Prediction Guides.”
5. Select Scope: Choose “Narrow” (specific) or “Broad” (sensitive).
6. Preview Results: View results in the “Clinical Study Categories” column.
7. View All Results: Click “See all” link to view full results in PubMed.

Medical Genetics Searches

Medical Genetics filters limit retrieval to citations related to medical genetics topics. See Medical genetics search filters for strategies.

To use a Medical Genetics filter, add the filter name with [Filter] tag, e.g., Genetic Testing[Filter]. Available filters:

• Diagnosis
• Differential Diagnosis
• Clinical Description
• Management
• Genetic Counseling
• Molecular Genetics
• Genetic Testing
• Medical Genetics

Example: Search for sickle cell anemia using the Genetic Counseling filter:

sickle cell anemia AND genetic counseling[Filter]

Single Citation Matcher for Specific Article Retrieval

The Single Citation Matcher is a fill-in-the-blank form to find a citation when you have bibliographic details like journal name, volume, or page number.

• Access Single Citation Matcher: Click “Single Citation Matcher” on the PubMed homepage.
• Enter Information: Fill in the form fields with known citation details.
• Click Go.

More on using the Single Citation Matcher:

• The journal box has autocomplete, suggesting titles ranked by citation count in PubMed.
• If using the “Back” button after selecting a journal with special characters, clear and re-enter the title.
• Author box autocomplete suggests author names ranked by citation count. Full author names are searchable for articles from 2002 onward if available.
• Check “Only as first author” or “Only as last author” to refine author searches to these positions.

MeSH Database for Controlled Vocabulary Searching

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

Use the MeSH database to find MeSH terms, Subheadings, Publication Types, Supplementary Concepts, and Pharmacological Actions, and then build PubMed searches. You can search the MeSH database by MeSH Term, Entry Term, Subheading, Publication Type, Supplementary Concept, or Scope Note.

More about the MeSH database:

• Autocomplete in the search box.
• Results ranked by relevance, with exact MeSH Term matches listed first.
• Click MeSH term in “Summary” or choose “Full” display for detailed information, including Subheadings, Major MeSH Topic restriction, and hierarchy exclusion.
• “Year Introduced” shows when the term was added to MeSH. Indexing uses the vocabulary in place at indexing time, so term introduction year and citation publication date may differ.

Launching PubMed Searches from MeSH Database

To build a PubMed search from MeSH terms:

1. Search MeSH Database: Run a search in the MeSH database.
2. Select Terms: Check the boxes next to desired terms.
3. Add to Search Builder: Click “Add to search builder” in the PubMed search builder portlet.
4. Continue Adding Terms: Continue searching MeSH and adding terms to the PubMed builder using “Add to search builder” and Boolean dropdown.
5. Search PubMed: Click “Search PubMed” when finished.

NLM Catalog for Journal Information

The NLM Catalog provides details about journals in PubMed and other NCBI databases.

Click Journals in NCBI Databases on the NLM Catalog homepage or the “Journals” link on PubMed’s homepage to limit NLM Catalog results to journals referenced in NCBI databases.

See NLM Catalog help for more information.

E-utilities API for Programmatic Access

E-utilities are API tools for accessing NCBI data outside the web interface, useful for programmatic data retrieval. For large-scale data mining, download PubMed data for free from the FTP server. See terms and conditions for data users.

Citation Matcher API for PMID Retrieval

The PubMed Citation Matcher API finds PubMed identifiers (PMIDs) from citation data in structured or raw form, supporting three retrieval methods:

1. field: Fielded search using bibliographic info (journal, date, volume).
2. heuristic: Heuristic search using all input elements as a single string.
3. auto: Combines field then heuristic if field fails (default method).

More about the Citation Matcher API:

• Supports GET and POST requests.
• Data exchange in JSON, UTF-8 encoded.
• Maximum 20 PMIDs returned per query.

API Root

The API root URL is:

https://pubmed.ncbi.nlm.nih.gov/api/citmatch/

Fielded Search (method=field)

Runs a structured search using bibliographic fields. Similar to E-utilities ESearch.

Usable fields:

• journal
• pdat (YYYY/MM/DD)
• volume
• issue
• authors (“Surname Initial,” position: first, last, auto optional).

Example fielded search:

https://pubmed.ncbi.nlm.nih.gov/api/citmatch/?method=field&journal=Front%20Immunol&volume=13&page=826091

Heuristic Search (method=heuristic)

Collects all input into a single string to find closest matches. Input raw citation string like: “The role of drag in insect hovering. J. Exp. Biol. 2004;207:4147–4155.”

Example heuristic search:

https://pubmed.ncbi.nlm.nih.gov/api/citmatch/?method=heuristic&raw-text=Neurogenesis%20and%20Viral%20Infection.%20Front%20Immunol.%202022%20Feb%2017;13:82609

Auto Search (method=auto)

Default method; first uses fielded search, then heuristic search if no results found. Uses the same structured fields as field method.

Example auto search:

https://pubmed.ncbi.nlm.nih.gov/api/citmatch/?method=auto&journal=Front+Immunol&volume=13&page=826091&authors=Ranganathan+S

API Rate Control

Limit programmatic API usage to 3 requests/sec and avoid concurrent requests. Include project name in User-Agent HTTP header (e.g., Hydra/1.3.15).

Batch Citation Matcher for Multiple PMID Retrieval

Use the Batch Citation Matcher to get PMIDs for multiple citations in batch. Input bibliographic info in a specific format.

To retrieve PMIDs:

1. Format Citation Strings: Create strings like: journal_title|year|volume|first_page|author_name|your_key|. Fields separated by |, ending with |.
2. Enter Email: Provide your email address for results delivery.
3. Input Citations: Upload a .txt file or enter strings in the text box (one per line).
4. Click Search.

If no match is found, results will include:

• your_key|NOT_FOUND;INVALID_JOURNAL: Invalid journal name. Check journal lists or NLM Catalog.
• NOT_FOUND: Valid journal, but no match for citation details.
• AMBIGUOUS: Multiple matches found. PMIDs provided for <=3 matches; count provided for >3. Use Single Citation Matcher or ESearch for all matches.

Notes for Batch Citation Matcher:

• Use .txt format for file uploads.
• Large searches may result in multiple emails.
• Author names: no punctuation, e.g., smith jc. Initials optional.
• “Your key” is a tag you provide, returned unchanged in results.
• Journal title: use full title or NLM abbreviation.
• Journal title is required; other fields optional but retain | separators if omitting fields.
• Search proceeds field by field until a unique match is found, starting with journal title.

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|
...

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
...

Consumer Health Information

NLM cannot give medical advice. For medical questions, consult a healthcare professional. NLM does not distribute pamphlets.

MedlinePlus and MedlinePlus en español are designed for consumer health information, with topic pages, videos, health tools, drug/supplement info, and links to NIH/CDC fact sheets.

Appendices: Further Help and Technical Details

Getting Further Assistance and Training

Contact Customer Support

• Email: PubMed Help Desk
• Phone: NLM Customer service desk: 1-888-FIND-NLM (1-888-346-3656)

Other NLM Publications

Refer to additional NLM publications and online resources for in-depth information on PubMed and related services.

How PubMed Works: Automatic Term Mapping (ATM)

Untagged search terms are processed by Automatic Term Mapping (ATM) against these tables in order: Subject translation table, Journals translation table, Author index, and Investigator (Collaborator) index. Mapping stops after a match in any table.

Check Search Details in Advanced Search to see term translation. For inaccurate translations, email NLM Help Desk.

1. Subject Translation Table

Contains:

• British/American spellings
• Singular/plural forms, synonyms, related terms
• Drug brand to generic name translations
• MeSH terms
• MeSH entry terms (See-Reference mappings)
• MeSH Subheadings
• Publication Types
• Pharmacologic action terms
• Synonyms from Unified Medical Language System (UMLS)
• Supplementary concept (substance) names and synonyms

Matches in this table search as MeSH terms (including MeSH term and narrower terms) and in all fields. Example: “child rearing” translates to "child rearing"[MeSH Terms] OR ("child"[All Fields] AND "rearing"[All Fields]) OR "child rearing"[All Fields].

If a MeSH Term is also a Pharmacologic Action, it searches as [MeSH Terms], [Pharmacologic Action], and [All Fields].

Entry term searches include an all-fields search for the associated MeSH term. Example: “odontalgia” translates to "toothache"[MeSH Terms] OR "toothache"[All Fields] OR "odontalgia"[All Fields] OR "odontalgias"[All Fields].

Substance name mappings do not map individual terms in phrases (e.g., “IL-22” does not map “IL” and “22” separately). MeSH term mappings with standalone numbers or single characters also don’t map individual terms (e.g., “Protein C” does not map “Protein” or “C” separately).

2. Journals Translation Table

Contains:

• Full journal title
• Title abbreviation
• ISSN and eISSN

Automatically maps to journal abbreviation for journal searches and all fields. Example: “endocrine pathology” translates to "Endocr Pathol"[Journal] OR ("endocrine"[All Fields] AND "pathology"[All Fields]) OR "endocrine pathology"[All Fields].

3. Author Index

If no match is found in prior tables, and the term is not a single word, PubMed checks the author index for author names and initials and full names (from 2002 onwards).

Author search details:

• Automatic truncation for initials (e.g., “o’brien j” retrieves “o’brien ja,” etc.).
• For multiple authors, use initials or [au] tag to avoid full name matches (e.g., ryan[au] james[au]). Stopwords as author names (e.g., “as a”) are ignored unless only the author name is searched.
• Full author name search in natural or inverted order (julia s wong or wong julia s).
• Comma after last name is optional, but may be needed for disambiguation (james, ryan).
• Omit periods in initials; suffixes at the end (vollmer charles jr). Initials/suffixes optional.
• Use [fau] to distinguish author initials from full names (e.g., peterson do[fau]).

4. Investigator (Collaborator) Index

If no match in prior tables (except Author) and not a single word, the investigator index is checked for full investigator names. Full names can be in natural or inverted order (harry janes or janes harry).

5. If No Match Is Found?

PubMed breaks down the phrase and repeats ATM. Stopwords are ignored. If still no match, individual terms are combined with AND and searched in all fields.

If a search with field tags retrieves zero results, PubMed retries with “Schema: all,” removing field tags and searching all terms in all fields.

Algorithm for Best Match Citation Ranking

The Best Match algorithm uses over 150 signals to rank results, mainly from query-document term pairs (term matches) and document/query-specific features (publication year, query length). A machine-learning model, trained on relevance data from PubMed search logs, refines the ranking.

For more details on the Best Match algorithm:

PubMed Coverage: MEDLINE, PMC, Bookshelf

PubMed indexes biomedical literature, covering:

For more info, see NLM Fact Sheet: Medline, PubMed, and PMC (PubMed Central): How are they different?

PubMed includes original research, reviews, case reports, letters, editorials, commentaries, and more (see publication types found in PubMed). Excluded content includes book reviews, conference abstracts, obituaries, news, and brief research summaries. See XML Help for PubMed Data Providers.

MEDLINE

MEDLINE covers life sciences with a focus on biomedicine, from the late 1940s to present.

New citations from MEDLINE journals are added daily, progressing through “in-process” to “indexed for MEDLINE.” Some citations from MEDLINE journals are not MEDLINE-indexed (e.g., pre-MEDLINE journal articles, out-of-scope articles). MEDLINE-indexed citations are updated with MeSH terms and other indexing data daily. Use medline[sb] to limit searches to MEDLINE citations.

Indexing Method

MeSH indexing methods have evolved. See Incorporating Values for Indexing Method in MEDLINE/PubMed XML. Searches for indexing methods:

PubMed Central (PMC)

PubMed Central (PMC) is a full-text archive of journals selected by NLM, individual articles, and preprints compliant with funder policies. Some PMC content is not in PubMed (e.g., book reviews).

Preprints

Since June 2020, PMC includes preprints of NIH-funded research, with citations in PubMed. See NIH Preprint Pilot.

Example: Search for preprints on COVID-19:

covid-19 AND preprint[pt]

Exclude preprints:

covid-19 NOT preprint[pt]

NCBI Bookshelf

Bookshelf is a full-text archive of biomedical books, reports, and databases. PubMed cites books and some chapters from Bookshelf.

PubMed Format Tags

The PubMed Format tags table lists data tags in PubMed format, in alphabetical order. Not all tags are in every record. Some tags (AU, MH, RN) may repeat. Download records in PubMed format as .txt or .nbib files (for citation management software). Not all fields are searchable; see Search field tags for searchable fields.

PubMed Format tags
Tag
AB
AD
AID
AU
AUID
BTI
CI
CIN
CN
COI
CON
CP
CRDT
CRF
CRI
CTDT
CTI
DCOM
DDIN
DRIN
DEP
DP
DRDT
ECF
ECI
EDAT
EFR
EIN
ED
EN
FAU
FED
FIR
FPS
GN
GR
GS
IP
IR
IRAD
IS
ISBN
JID
JT
LA
LID
LR
MH
MHDA
MID
NM
OAB
OABL
OCI
OID
ORI
OT
OTO
OWN
PB
PG
PHST
PL
PMC
PMCR
PMID
PS
PST
PT
RF
RIN
RN
ROF
RPF
RPI
RRI
RRF
SB
SFM
SI
SO
SPIN
STAT
TA
TI
TT
UIN
UOF
VI
VTI

PubMed Data Field Descriptions

PubMed record field descriptions with search tags (where applicable). Some searchable fields don’t directly correspond to PubMed format fields.

Affiliation [ad]

Author, corporate author, investigator affiliations. Multiple affiliations added from 2014. “Contributed equally” note included if provided. Searches all author affiliations. Proximity searches recommended for multi-term affiliations (e.g., "Hopkins Bloomberg Public"[ad:~45]).

All Fields [all]

Untagged terms and [all] are processed by Automatic Term Mapping (ATM). Unmapped terms are searched in all fields except Place of Publication, Create Date, Completion Date, Entry Date, MeSH Date, Modification Date. Double quotes or wildcards bypass ATM. Stopwords are ignored.

Article Identifier [aid]

Publisher-submitted article IDs like DOI.

Author [au]

Format: last name, space, up to two initials, space, suffix (no periods/commas). Initials/suffixes optional. Automatic truncation; use double quotes and [au] to disable (e.g., "o'brien j"[au]). Full name search possible from 2002 onward.

Author Identifier [auid]

Unique author identifier (ORCID, ISNI, VIAF), e.g., orcid 0000-0001-5027-4446 [auid].

Book [book]

Book citations, e.g., genereviews[book]. Untagged searches for books/chapters: pmcbook (books and chapters), pmcbooktitle (books), pmcbookchapter (chapters). For comprehensive book searches, use "pubmed books"[sb].

Comment Correction Type

Citations to related publications (comments, errata). Search terms: hascommentin, hascommenton, hascorrectedrepublishedin, etc.

Completion Date [dcom]

NLM internal processing date. Not in All Fields; requires [dcom] tag.

Conflict of Interest Statement [cois]

Statement from article. Available if provided by publisher or in PMC full text. Query hascois to find citations with COI statements.

Corporate Author [cn]

Corporate or collective authorship. Displays as in journal. Citations pre-2000 and some 2000-2001 may have corporate authors in the title field.

Create Date [crdt]

Date citation created in PubMed. Useful for recent additions. Not in All Fields; requires [crdt] tag.

EC/RN Number [rn]

Numbers from FDA, Enzyme Commission (EC), Chemical Abstracts Service (CAS). Includes Registry and Related Registry Numbers.

Editor [ed]

Editors for book/chapter citations.

Entry Date [edat]

Date citation added to PubMed, used for “Most Recent” sort. Typically within 24 hours of availability. After Dec 15, 2008, citations added >12 months post-publication have EDAT set to publication date (except books). Before then, EDAT was Publication Date for citations before Sept 1997. Not in All Fields; requires [edat] tag. (Legacy PubMed called this “Entrez Date”).

Filter [filter] [sb]

LinkOut, filter tags: loall[sb] (LinkOut links), free full text[sb], full text[sb].

First Author Name [1au]

First personal author name.

Full Author Name [fau]

Full author name from 2002 onwards, if available. Natural or inverted order.

Full Investigator Name [fir]

Full investigator name, if available. Natural or inverted order.

Grants and Funding [gr]

Grant, contract, intramural project numbers. Parts: Number, Funder code, Agency, Country. Each part searchable with [gr]. Example: CA101211[gr], NCI[gr]. "intramural nih"[gr] for intramural NIH staff articles. Completeness varies by source.

Investigator [ir]

Principal investigator or collaborator names. Format like author field, e.g., soller b[ir].

ISBN [isbn]

ISBN for books/chapters.

Issue [ip]

Journal issue number.

Journal [ta]

Journal title abbreviation, full title, ISSN/eISSN (e.g., J Biol Chem, Journal of Biological Chemistry, 0021-9258). Omit special characters in titles (e.g., J Hand Surg Am not J Hand Surg [Am]).

Language [la]

Article language. Use language name or first three letters (e.g., chi[la] or chinese[la]). Exception: jpn[la] for Japanese.

Last Author Name [lastau]

Last personal author name.

Location ID [lid]

DOI or publisher ID as pagination for online articles.

MeSH Date [mhda]

Date citation indexed with MeSH terms. Set to Entry Date initially. Not in All Fields; requires [mhda] tag. Format: YYYY/MM/DD [mhda]. Range format: 1999:2000 [mhda].

MeSH Major Topic [majr]

MeSH term that is a main article topic, marked with asterisk. See MeSH Terms [mh].

MeSH Subheadings [sh]

MeSH Subheadings refine MeSH terms. Example: asthma/drug therapy. “Free float” Subheadings (e.g., hypertension[mh] AND toxicity[sh]). Automatically includes narrower Subheadings. Disable with [sh:noexp] (e.g., therapy[sh:noexp]). Use two-letter abbreviations (e.g., dh[sh] = diet therapy[sh]).

MeSH Terms [mh]

NLM Medical Subject Headings. Updated annually. Hierarchical structure. Automatically includes narrower terms. Disable with [mh:noexp] (e.g., neoplasms[mh:noexp]). Use [mh] or [majr] tags for MeSH term searches. MeSH/Subheading combinations: MeSH Term/Subheading (e.g., neoplasms/diet therapy). Use two-letter Subheading abbreviations (e.g., neoplasms/dh). For embedded parentheses, replace with space and use [mh] (e.g., benzo a pyrene [mh] for Benzo(a)pyrene). Searchable in MeSH database and advanced search builder.

Modification Date [lr]

Citation’s last revision date. Not in All Fields; requires [lr] tag.

NLM Unique ID [jid]

NLM journal ID, e.g., 0375267[jid].

Other Term [ot]

Author keywords (OT field). Searchable with [tiab], [tw], [ot]. Query haskeyword to find citations with keywords. May indicate major concept with asterisk, but major concept tag not searchable for Other Terms.

Owner

Organization supplying citation data. Search: owner + acronym (e.g., ownernasa).

Pagination [pg]

First page number. Citation displays full pagination, but searchable by first page only.

Personal Name as Subject [ps]

Limits search to articles where the name is the subject, e.g., varmus h[ps]. Format like author field.

Pharmacological Action [pa]

Substances with a specific pharmacologic action. Includes MeSH terms and Supplementary Concept Records.

Place of Publication [pl]

Country of journal publication. Geographic regions not searchable. Search individual countries in a region with OR. Not in all fields or text word retrieval.

PMCID and MID

Search PMC/NIHMS IDs with prefix and number, e.g., PMC2600426. Query hasnihmsid for all NIH manuscript citations.

PMID [pmid]

PubMed Identifier. Search with or without [pmid] tag (e.g., 17170002 or 17170002[pmid]). Multiple PMIDs ORed with spaces (e.g., 17170002 16381840). PMIDs are permanent and unique.

Publication Date [dp]

Article publication date. [dp] and [pdat] tags interchangeable. Format: yyyy/mm/dd [dp]. Month/day optional. Date ranges: 1996:1998 [dp]. Relative dates: "last X days"[dp], "last X months"[dp], "last X year"[dp].

Publication Type [pt]

Article type (Review, Clinical Trial, etc.). Use [pt] tag with Publication Type, e.g., review[pt]. Hierarchical; includes narrower types. Disable narrower types with [pt:noexp] (e.g., review[pt:noexp]).

Publisher [pubn]

Publisher names for Bookshelf citations.

Secondary Source ID [si]

Databanks and accession numbers (GenBank, GEO, ClinicalTrials.gov). Format: source/accession. Searchable with source, accession, or both (e.g., genbank[si], AF001892[si], genbank/AF001892[si]). Query hasdatabanklist for all citations with SI values.

Subset [sb]

Restricts retrieval by subject, citation status, journal category. See filters and LinkOut resources.

Supplementary Concept [nm]

Chemical, protocol, disease, organism terms. Synonyms map automatically with [nm]. Implemented mid-1980s; many chemicals searchable as MeSH terms before then.

Text Words [tw]

Words/numbers in title, abstract, other abstract, MeSH terms, Subheadings, Publication Types, Substance Names, Personal Name as Subject, Corporate Author, Secondary Source, Comment/Correction Notes, Other Terms (keywords).

Title [ti]

Words/numbers in article title, book collection title.

Title/Abstract [tiab]

Words/numbers in title, collection title, abstract, other abstract, author keywords (Other Term [ot] field). English abstracts from article. NLM does not create abstracts if not provided.

Transliterated Title [tt]

Non-English title in original language, transliterated. Not in Text Word [TW] retrieval.

Volume [vi]

Journal volume number.

NLM Author Indexing Policy

NLM author indexing policy over time:

• 1966-1984: No author limit.
• 1984-1995: Limit of 10 authors, “et al” for 11th+.
• 1996-1999: Limit of 25 authors, “et al” for 26th+.
• 2000-Present: No author limit.

More information:

• From mid-2005, past year limits lifted; citations may be edited to include all authors.
• From 1992, letters indexed individually, not as anonymous groups.
• Until 1990, NLM transliterated up to 5 Cyrillic/Japanese author names.
• 1990-2016, first 10 Cyrillic/Japanese names transliterated. Chinese ideograms not transliterated unless transliterations available in article/TOC.
• From 2016, author names in Roman characters in all MEDLINE journals; NLM no longer transliterates Cyrillic/Japanese. All author names included as published.

Error Messages

System Error Messages

Consult IT staff for browser advice to ensure JavaScript, cookies, pop-ups, HTTP 1.1 are enabled. Antivirus may affect caching. Add nlm.nih.gov as browser exception/trusted site. Clear browser cache.

Typographical Errors

Report errors to journal publisher for correction in PubMed (except MeSH errors). For MeSH errors, contact NLM Help Desk with PMID and error details. NLM data distributed to vendors may not reflect immediate corrections. Contact vendors for their update schedules.

Cookies

“Cookies” are website server information stored on your computer. See NLM Privacy Policy. PubMed uses cookies for interactive features. Enable cookies in browser settings. Cookie-dependent feature issues may be due to:

• Cookies blocked by provider/institution. Check with provider/admin if cookies are blocked.
• Incorrect computer date/time settings. Verify computer time settings.

MeSH Subheadings

MeSH Subheadings table and scope notes/categories.

Abbreviation	MeSH Subheading	Abbreviation	MeSH Subheading
AB	Abnormalities	IR	Innervation
AD	Administration and Dosage	IS	Instrumentation
AE	Adverse Effects	IP	Isolation and Purification
AG	Agonists	LJ	Legislation and Jurisprudence
AA	Analogs and Derivatives	ME	Metabolism
AN	Analysis	MT	Methods
AH	Anatomy and Histology	MI	Microbiology
AI	Antagonists and Inhibitors	MO	Mortality
BI	Biosynthesis	NU	Nursing
BS	Blood Supply	OG	Organization and Administration
BL	Blood	PS	Parasitology
CF	Cerebrospinal Fluid	PY	Pathogenicity
CS	Chemical Synthesis	PA	Pathology
CI	Chemically Induced	PK	Pharmacokinetics
CH	Chemistry	PD	Pharmacology
CL	Classification	PH	Physiology
CO	Complications	PP	Physiopathology
CN	Congenital	PO	Poisoning
CY	Cytology	PC	Prevention and Control
DF	Deficiency	PX	Psychology
DI	Diagnosis	RE	Radiation Effects
DH	Diet Therapy	RT	Radiotherapy
DG	Diagnostic Imaging	RH	Rehabilitation
DE	Drug Effects	SC	Secondary
DT	Drug Therapy	ST	Standards
EC	Economics	SN	Statistics and Numerical Data
ED	Education	SD	Supply and Distribution
EM	Embryology	SU	Surgery
EN	Enzymology	TU	Therapeutic Use
EP	Epidemiology	TH	Therapy
ES	Ethics	TO	Toxicity
EH	Ethnology	TM	Transmission
ET	Etiology	TR	Transplantation
GE	Genetics	TD	Trends
GD	Growth and Development	UL	Ultrastructure
HI	History	UR	Urine
IM	Immunology	VE	Veterinary
IN	Injuries	VI	Virology

Stopwords

Stopwords table.

PubMed Character Conversions

Special characters in searches and their conversions.

Searches with these characters are translated:

• () – Boolean nesting
• [] – Search field tag
• & – AND
• | – OR
• / – MeSH/Subheading
• : – Range operation
• " – Phrase search
• # – History search (e.g., #1 AND cat)
• * – Wildcard (e.g., toxicol*)

Characters converted to spaces: ! # $ % * + - . , ; < > = ? ^ _ { } ~ '

Special characters in MeSH fields: / - ,

Publication Types

Publication types list. See Publication Type [PT] and MeSH Publication Types with Scope Notes. Not all MeSH Publication Types are in PubMed.

Status Subsets

Status Subsets table. Search terms and citation status descriptions.

Filter Search Strategies

Filter search strategies tables for Publication date, Text availability, Article attribute, Article type, Article language, Species, Sex, Age, Other, Clinical Queries filters.

Clinical Queries Filters

Clinical Queries filters tables for COVID-19 Article Filters and Clinical Study Categories.

Computation of Similar Articles

Computation of similar articles explanation. Algorithm details for similar article finding.

Journal Lists

Journal lists links for PubMed and NCBI molecular biology database journals.

Conclusion: Mastering PubMed for Your Research Needs

This user guide has provided a detailed overview of PubMed, from basic search functionalities to advanced features and tools. By understanding and applying the techniques outlined, you can significantly enhance your ability to navigate the vast landscape of biomedical literature efficiently and effectively. PubMed is more than just a database; it is a gateway to a wealth of scientific knowledge, crucial for advancing research, clinical practice, and health education.

As you continue to use PubMed, remember to explore its various features and experiment with different search strategies to refine your skills. Regularly checking the “PubMed New and Noteworthy” updates will also keep you informed of the latest enhancements and capabilities. Whether you are a seasoned researcher or just beginning your journey into biomedical literature, PubMed is an indispensable resource, and mastering it is a valuable asset in today’s information-rich world. Start exploring PubMed today and unlock the power of biomedical knowledge at your fingertips.