MeSH Terms
What Are MeSH Terms?
Medical Subject Headings (MeSH) is a comprehensive controlled vocabulary for the purpose of indexing journal articles and books in the life sciences. It serves as a thesaurus of index terms that facilitates searching. Created and updated by the United States National Library of Medicine (NLM), it is used by the MEDLINE (Medical Literature Analysis and Retrieval System Online) and PubMed article database.
MeSH contains approximately 30,000 entries (as of 2025) and is updated annually to reflect changes in medicine and medical terminology. These standardized terms ensure consistent indexing and retrieval of medical literature across all healthcare disciplines.
Why MeSH Terms Matter for Healthcare Professionals
Precision in Medical Literature Searches
One of the biggest advantages of using MeSH terms is that all MeSH terms are pre-defined and have synonyms included. MeSH is effective for searching for meaning, rather than only looking for where words appear in the abstract text. This is particularly valuable for healthcare professionals who need to find comprehensive, relevant research quickly.
Standardized Medical Terminology
The Medical Subject Heading (MeSH) is a controlled and hierarchically-organized vocabulary produced by the National Library of Medicine. It is used to give uniformity and consistency to the indexing, cataloging, and searching of biomedical and health-related information in PubMed, MEDLINE, and other NLM databases.
Example of MeSH Precision
For instance, when searching for the MeSH term "telemedicine," it includes the synonyms (i.e. entry terms) "mobile health," "mhealth," "telehealth," and "ehealth." This comprehensive coverage ensures practitioners don't miss relevant articles due to varying terminology.
How MeSH Works in the Research Library
Automatic Term Mapping
When performing a MEDLINE search via PubMed, entry terms are automatically translated into (i.e., mapped to) the corresponding descriptors with a good degree of reliability. KopplaHQ Research Library leverages this same system through its PubMed API integration.
Article Indexing Process
MeSH headings are assigned to citations by subject specialists at the National Library of Medicine. Prior to April 2022, the majority of MEDLINE records were indexed by human indexers. Since April 2022 all MEDLINE records in PubMed are assigned MeSH terms using automated indexing. Human indexers still check the quality of selected sets of automatically indexed citations.
Coverage and Timing
In MEDLINE/PubMed, every journal article is indexed with about 10–15 subject headings, subheadings and supplementary concept records, with some of them designated as major and marked with an asterisk, indicating the article's major topics.
MeSH Structure and Hierarchy
Hierarchical Organization
MeSH terms are arranged in alphabetic order and in a hierarchical structure by subject categories with more specific terms arranged beneath broader terms. When searching for a MeSH term, the most specific MeSH terms are automatically included in the search.
Tree Structure Categories
The top-level categories in the MeSH descriptor hierarchy are:
| Code | Category |
|---|---|
| A | Anatomy |
| B | Organisms |
| C | Diseases |
| D | Chemicals and Drugs |
| E | Analytical, Diagnostic and Therapeutic Techniques, and Equipment |
| F | Psychiatry and Psychology |
| G | Phenomena and Processes |
| H | Disciplines and Occupations |
| I | Anthropology, Education, Sociology and Social Phenomena |
| J | Technology, Industry, and Agriculture |
| K | Humanities |
| L | Information Science |
| M | Named Groups |
| N | Health Care |
| V | Publication Characteristics |
| Z | Geographicals |
Automatic Term Expansion
When searching using a MeSH term, PubMed automatically searches for the specific term and all subcategories beneath it. This is called "exploding" the subject heading.
Practical Application in Research Library
Finding MeSH Terms in Search Results
When finding a relevant article in PubMed, practitioners can examine its MeSH terms to identify those for use in search strategies. An article's MeSH terms appear in its full record or Abstract view.
Using the MeSH Database
To search MeSH, click on MeSH Database under Explore on near the bottom of the PubMed main page. In the Research Library context, this feature helps identify the most precise terms for clinical research needs.
Search Strategy Recommendations
Optimal searches combine both keywords and MeSH terms. The most recent articles in PubMed do not have MeSH terms attached to them yet. To ensure the most recent literature appears in results, combine MeSH terms with keywords using the boolean operator OR. When searching for literature, it is important to use both MeSH terms and textwords (i.e. synonyms gathered from Step 2). This is because not all articles, especially those that are recently published, have been assigned MeSH terms.
MeSH Subheadings and Qualifiers
Enhanced Search Precision
MeSH also contains a small number of standard qualifiers (also known as subheadings), which can be added to descriptors to narrow down the topic. For example, "Measles" is a descriptor and "epidemiology" is a qualifier; "Measles/epidemiology" describes the subheading of epidemiological articles about Measles. The "epidemiology" qualifier can be added to all other disease descriptors.
Available Qualifiers
In all there are 83 different qualifiers. Common qualifiers relevant to healthcare research include:
- Drug therapy
- Diagnosis
- Epidemiology
- Prevention & control
- Adverse effects
- Therapeutic use
Important Considerations for Recent Literature
Indexing Delays
It takes time to apply subject headings to citations: For this reason, newer citations do not yet have subject headings. There is usually a delay of a month or two between an article being added to PubMed and when it is indexed with MeSH terms.
Historical Limitations
MeSH is not retroactive: When a new subject heading is introduced, NLM staff do not go back through previous years to apply the heading to earlier citations. You can tell how old a MeSH term is by looking at the "Year introduced" field.
Best Practices for Healthcare Professionals
Comprehensive Search Strategy
- Start with MeSH terms for established concepts and proven interventions
- Add keyword searching to capture recent literature and alternative terminology
- Use the "Free Full Text Only" filter when combining with MeSH searches
- Review MeSH terms from relevant articles to refine search strategies
Clinical Application Tips
- For established conditions: Use specific MeSH terms (e.g., "Diabetes Mellitus, Type 2")
- For interventions: Combine condition MeSH with treatment subheadings
- For new treatments: Supplement MeSH searches with keyword variants
- For systematic reviews: Document the MeSH strategy for reproducibility
Quality Assurance
MeSH enables searchers to create powerful and unambiguous MEDLINE queries. This precision is essential for evidence-based practice where comprehensive yet focused literature reviews directly impact patient care decisions.
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