Examples
Worked examples
- Is an instance
A peer-reviewed clinical journal is evaluated against MEDLINE's journal-selection criteria and accepted; from that point forward its articles are assigned MeSH terms and are retrievable as MEDLINE citations within PubMed.
- Is an instance
A researcher searching PubMed by a MeSH heading retrieves citations across many different MEDLINE-indexed journals and publishers, because the search matches NLM's controlled vocabulary rather than free-text keywords alone.
Counter-examples
Looks similar, but isn't
- Not an instance
An NIH-funded manuscript in a journal that is NOT MEDLINE-indexed can still appear in PubMed and have a free full text, because it was deposited in PubMed Central under the NIH Public Access Policy -- it is discoverable via PubMed but is not a MEDLINE citation and was never evaluated by NLM's journal-selection process.
Editorial commentary
MEDLINE is the U.S. National Library of Medicine’s (NLM) core bibliographic database of biomedical and life-sciences journal literature. It is not a search engine or a website in its own right — it is a curated dataset of citations (title, authors, abstract, and controlled-vocabulary subject terms) drawn only from journals that have individually passed NLM’s journal-selection review. That review-gated inclusion is what distinguishes a “MEDLINE journal” from the much larger set of journals merely searchable through PubMed.
MEDLINE vs. PubMed vs. PMC
These three names are often used interchangeably, but they describe three different things, and conflating them is one of the most common indexing-literacy mistakes researchers and journal editors make:
- MEDLINE is the bibliographic database itself — the curated set of citations from journals NLM has formally selected for indexing. It contains more than 31 million references to journal articles, drawn from over 5,200 journals worldwide in roughly 40 languages, with coverage from 1966 to the present (selected earlier citations appear in OLDMEDLINE).
- PubMed is the free search interface, developed and maintained by NLM’s National Center for Biotechnology Information (NCBI). MEDLINE is PubMed’s largest and most heavily used component, but PubMed also contains records PubMed itself does not classify as MEDLINE citations — for example, in-process citations awaiting full indexing, and citations to articles in journals that are not MEDLINE-indexed but that are deposited in PubMed Central under an NIH public-access mandate. Searching PubMed is not the same as searching only MEDLINE.
- PubMed Central (PMC) is NLM’s free full-text archive. It is a repository of article content, not a bibliographic index, and its inclusion criteria are separate from — and less restrictive than — MEDLINE’s journal-selection criteria. A journal can be in PMC without being MEDLINE-indexed (common for journals participating in the NIH Public Access Policy), and a MEDLINE-indexed article does not automatically have a free full text in PMC unless the publisher or a funder mandate puts it there.
See CASRAI’s related guide on what it means for a journal to be indexed for how MEDLINE selection compares to Scopus, Web of Science, and DOAJ criteria.
History: from Index Medicus to MEDLINE
MEDLINE is the online successor to a print lineage that predates computerized indexing by nearly a century. NLM published Index Medicus, a print index to biomedical journal articles, starting in 1879. NLM computerized this indexing work as MEDLARS (Medical Literature Analysis and Retrieval System) in 1964, and MEDLINE — MEDLARS Online — became the searchable online counterpart built on that same indexing infrastructure. Index Medicus itself ceased print publication in 2004 once MEDLINE/PubMed had fully superseded it as the primary access point, but the two share the same underlying editorial lineage and the same controlled vocabulary.
How NLM decides what enters MEDLINE
Journal selection for MEDLINE is, in NLM’s own description, a “rigorous, multi-step process” that evaluates a journal comprehensively rather than against a single checklist. Criteria span scope and scientific merit, editorial work and content (including a clearly stated, sufficiently detailed peer-review policy), and production quality. A clearly documented peer-review process is one explicit factor within that evaluation — not a standalone pass/fail gate on its own — which is why MEDLINE indexing is a reasonably strong signal of editorial rigor but not a certification of peer review for any single article.
Historically, external review of MEDLINE-candidate journals was handled by the Literature Selection Technical Review Committee (LSTRC), a 15-member NIH-chartered federal advisory committee established in 1987. NLM disbanded the LSTRC in September 2025 as part of a stated modernization of operations, replacing the standing committee with external subject-matter and medical-library consultants for journal review going forward. The underlying selection criteria (scope, scientific merit, editorial quality) are unchanged; what changed is who applies them.
Selection is journal-level, not article-level: once a journal is accepted, its qualifying articles going forward (and sometimes retrospectively) become MEDLINE citations. NLM can also discontinue indexing a journal that no longer meets its criteria.
MeSH: MEDLINE’s controlled vocabulary
Every MEDLINE citation is indexed using Medical Subject Headings (MeSH), NLM’s controlled, hierarchical vocabulary for biomedical concepts. MeSH terms are what let PubMed searches retrieve conceptually related articles even when they don’t share exact keywords — a search for a MeSH heading returns everything indexed under that concept, including narrower terms beneath it in the hierarchy. This subject indexing is one of the concrete products of MEDLINE inclusion that a merely-PubMed-discoverable, non-MEDLINE citation does not receive.
Worked examples
- Example: A peer-reviewed clinical journal applies to NLM, is evaluated against MEDLINE’s journal-selection criteria, and is accepted. From that point forward, its articles are assigned MeSH terms and retrievable as MEDLINE citations within PubMed — this is what a publisher means when it advertises a journal as “MEDLINE-indexed.”
- Example: A researcher searching PubMed for a MeSH heading retrieves citations from many different MEDLINE-indexed journals across publishers, because the search is matching NLM’s controlled vocabulary rather than free-text keywords alone.
Counter-example
An NIH-funded manuscript accepted by a journal that is not MEDLINE-indexed can still appear in a PubMed search and have a free full text, because the author deposited the manuscript in PubMed Central under the NIH Public Access Policy. That record is discoverable through PubMed and archived in PMC, but it is not a MEDLINE citation and was not evaluated by NLM’s journal-selection process — a useful reminder that “in PubMed” and “in MEDLINE” are not the same claim.
Related terms
Academic journal · DOAJ · Web of Science · NIH Public Access Policy · What does it mean for a journal to be indexed? · How to know if an article is peer reviewed
Machine-readable encodings
Use in your systems
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