MEDLINE (Medical Literature Analysis and Retrieval System Online) is the premier bibliographic database of the U.S. National Library of Medicine (NLM), which is part of the National Institutes of Health (NIH).

MEDLINE contains more than 28 million references to journal articles in life sciences, with a strong concentration on biomedicine. It is the most authoritative and widely used biomedical literature database in the world.

The database indexes articles from approximately 5,200 biomedical journals published in over 40 languages worldwide, though the majority of records are from English-language sources or have English abstracts.

MEDLINE records are indexed with NLM's Medical Subject Headings (MeSH), a controlled vocabulary thesaurus containing over 29,000 descriptors. This standardized indexing enables precise and efficient literature searching across the biomedical field.

MEDLINE is the primary component of PubMed, the freely accessible search engine that provides access to MEDLINE records along with additional content from PubMed Central and other NLM resources.

PubMed is a free search engine developed and maintained by the National Center for Biotechnology Information (NCBI) at the National Library of Medicine. It was first released in January 1996 and has since become the most widely used biomedical literature search tool in the world.

PubMed contains over 35 million citations and abstracts of biomedical literature. It is important to understand that PubMed is broader than MEDLINE — PubMed includes MEDLINE records plus additional content:

MEDLINE Records: The core of PubMed — approximately 28 million references from 5,200+ journals indexed with MeSH terms by NLM indexers.

PubMed Central (PMC) Records: Full-text articles from the PMC open access repository that may not be in MEDLINE-indexed journals.

In-Process Citations: Records that have been submitted but not yet fully indexed with MeSH terms.

Publisher-Supplied Citations: Records submitted directly by publishers before NLM processing.

Bookshelf Records: Citations from books and documents available on the NCBI Bookshelf.

The key distinction is that all MEDLINE records are in PubMed, but not all PubMed records are in MEDLINE. Being "PubMed indexed" may simply mean the article appears in PubMed, while being "MEDLINE indexed" specifically means the journal has undergone NLM's rigorous evaluation and its articles receive MeSH indexing.

The history of MEDLINE traces back to the Index Medicus, a comprehensive guide to medical literature first published by Dr. John Shaw Billings in 1879 at the Library of the Surgeon General's Office (now the National Library of Medicine).

In 1964, the NLM began computerizing the Index Medicus, creating an electronic database called MEDLARS (Medical Literature Analysis and Retrieval System). This was one of the first large-scale computerized bibliographic databases in any field.

In 1971, MEDLARS went online as MEDLINE (MEDLARS Online), making biomedical literature searchable electronically for the first time. Initially, searches could only be performed by trained librarians using dedicated terminals.

In 1996, the NLM launched PubMed, providing free public access to MEDLINE over the internet. This was a revolutionary step that democratized access to biomedical literature worldwide. Before PubMed, accessing MEDLINE required expensive institutional subscriptions.

In 2000, PubMed Central (PMC) was launched as a free digital repository of full-text biomedical and life sciences journal literature. PMC was created to comply with the NIH Public Access Policy requiring that research funded by NIH be made freely available.

In 2004, NLM introduced the LinkOut feature, allowing users to access full-text articles directly from PubMed through publisher websites and institutional subscriptions.

In 2020, PubMed underwent a major redesign with an updated interface, improved search algorithms, and enhanced mobile responsiveness, making it even more user-friendly for researchers worldwide.

Today, PubMed processes over 3 million searches per day and is used by researchers, healthcare professionals, students, and the public in virtually every country in the world.

PubMed Central (PMC) is a free full-text archive of biomedical and life sciences journal literature maintained by the National Center for Biotechnology Information (NCBI) at the National Library of Medicine.

Launched in 2000, PMC was created in response to the growing movement for open access to scientific literature. It provides permanent, free access to the full text of published research articles.

PMC currently contains over 8 million full-text articles from thousands of participating journals. It is important to note that PMC and MEDLINE are different:

MEDLINE is an index of journal citations with abstracts — it does not provide full-text articles. Articles are selected based on the journal being evaluated and accepted by NLM for MEDLINE indexing.

PMC is a full-text repository. Journals can deposit their content in PMC through various arrangements. Some journals deposit all their content, while others deposit only NIH-funded research articles (as required by the NIH Public Access Policy).

A journal can be in PMC without being indexed in MEDLINE, and a MEDLINE-indexed journal may or may not deposit full-text articles in PMC. However, many journals are both MEDLINE-indexed and participate in PMC.

For researchers, having an article available in PMC significantly increases its visibility and accessibility, as the full text is freely available to anyone worldwide.

Medical Subject Headings (MeSH) is the NLM's controlled vocabulary thesaurus used for indexing articles in MEDLINE/PubMed. MeSH is one of the most important features that distinguishes MEDLINE from other biomedical databases.

MeSH contains over 29,000 descriptors (main headings) organized in a hierarchical tree structure with 16 major categories. Each descriptor has a unique definition and can be further refined with subheadings (qualifiers) to specify aspects of a topic.

How MeSH Works: When a journal article is indexed in MEDLINE, trained NLM indexers read the article and assign the most appropriate MeSH terms to describe its content. Each article typically receives 10-15 MeSH terms, including both major topics (marked with an asterisk) and minor topics.

MeSH Tree Structure: MeSH terms are organized hierarchically from broad to specific. For example, under "Diseases" you would find "Cardiovascular Diseases" → "Heart Diseases" → "Coronary Disease" → "Myocardial Infarction". Searching a broader term automatically includes all narrower terms below it (called "exploding" the MeSH term).

Why MeSH Matters: MeSH indexing solves the problem of inconsistent terminology in biomedical literature. Different authors may use different words for the same concept (e.g., "heart attack", "myocardial infarction", "MI"). MeSH ensures that all articles about the same concept are grouped under one standardized term, making literature searches more comprehensive and precise.

MeSH is updated annually with new terms added to reflect advances in biomedical science and changes in medical terminology.

MEDLINE/PubMed indexing is considered one of the most prestigious achievements for biomedical journals. Here's why it matters:

1. Global Standard for Biomedical Literature: MEDLINE is recognized worldwide as the gold standard for biomedical literature indexing. Being MEDLINE-indexed signals that a journal has met the highest quality standards set by the National Library of Medicine.

2. Free Global Access via PubMed: Unlike subscription-based databases (Scopus, Embase, Web of Science), PubMed is completely free and accessible to everyone worldwide. This gives MEDLINE-indexed journals unparalleled visibility and reach.

3. Academic Career Requirements: Many universities, medical schools, and research institutions require publications in MEDLINE/PubMed-indexed journals for faculty promotions, PhD completions, and tenure decisions — especially in medical and health sciences fields.

4. Essential for Evidence-Based Medicine: PubMed is the primary tool used by healthcare professionals for evidence-based clinical decision-making. Having research indexed in MEDLINE ensures it reaches clinicians who use it to guide patient care.

5. Systematic Review Requirement: Major systematic review organizations including Cochrane require MEDLINE/PubMed as a mandatory search database. Research not indexed in MEDLINE may be excluded from important systematic reviews and meta-analyses.

6. Funding Agency Requirements: Many national and international health research funding agencies (NIH, WHO, Wellcome Trust) require or prefer publications in MEDLINE-indexed journals when evaluating grant applications and research output.

7. MeSH Indexing Quality: The expert MeSH indexing provided by NLM ensures that articles are accurately categorized and easily discoverable, increasing the long-term discoverability and citation potential of published research.

8. Credibility and Trust: MEDLINE's rigorous journal selection process, managed by the independent Literature Selection Technical Review Committee (LSTRC), ensures that only journals meeting strict quality criteria are included, making MEDLINE indexing a reliable indicator of journal quality.

Getting a journal indexed in MEDLINE is one of the most challenging indexing achievements. The process is managed by the Literature Selection Technical Review Committee (LSTRC), an NIH-chartered advisory committee. Here are the steps:

Step 1: Meet Scientific Scope Requirements – The journal must primarily publish articles in biomedical or health-related subjects that fall within the scope of NLM's collection. NLM covers medicine, nursing, dentistry, veterinary medicine, health care systems, pre-clinical sciences, and related life sciences.

Step 2: Demonstrate Quality of Content – The journal must publish original research, systematic reviews, or clinical studies of high scientific quality. The scientific merit of the published content is the most critical factor in the evaluation. Articles should demonstrate sound methodology, appropriate statistical analysis, and valid conclusions.

Step 3: Meet Editorial Standards – The journal must have a clearly described peer review process, an editorial board with recognized expertise, transparent editorial policies, adherence to ICMJE Recommendations and COPE guidelines, and proper handling of conflicts of interest.

Step 4: Demonstrate Publishing Quality – The journal must have a valid ISSN, publish on a regular schedule (no significant delays), provide English-language titles and abstracts for all articles, include complete author affiliations and contact information, and have a professional journal website.

Step 5: Build a Track Record – The journal should have been publishing consistently for at least 2-3 years before applying. NLM wants to see a stable publishing history with consistent quality.

Step 6: Submit Application – Submit the journal for MEDLINE evaluation through the NLM online application portal. The application requires detailed information about the journal's scope, editorial processes, review procedures, and publication history. You must also submit recent issues for review.

Step 7: LSTRC Review – The Literature Selection Technical Review Committee reviews the journal based on scientific quality, editorial standards, production quality, and audience. The LSTRC meets three times per year and the evaluation process typically takes 6-12 months.

Step 8: Decision – The journal receives one of three outcomes: Accepted for MEDLINE indexing, Not recommended for MEDLINE (with reasons provided), or Deferred for further review. Journals that are not accepted can reapply after addressing the identified issues.

Many researchers confuse MEDLINE, PubMed, and PubMed Central (PMC). Here is a clear comparison:

MEDLINE: A bibliographic database of approximately 28 million citations from 5,200+ journals. Articles are indexed with MeSH terms by NLM indexers. MEDLINE is accessed through PubMed. Only journals that pass LSTRC evaluation are included. MEDLINE provides citations and abstracts only — not full-text articles.

PubMed: A search engine/interface that provides free access to MEDLINE plus additional content. PubMed contains over 35 million records, including MEDLINE citations, in-process citations, publisher-supplied records, and PMC records. PubMed is broader than MEDLINE — having an article "in PubMed" does not necessarily mean the journal is "MEDLINE indexed."

PubMed Central (PMC): A full-text repository containing over 8 million free full-text articles. PMC is a separate archive — journals can participate in PMC without being MEDLINE-indexed, and vice versa. PMC participation requires journals to deposit full-text XML files.

Key Distinctions for Researchers:

• "MEDLINE indexed" = The journal has been evaluated and accepted by NLM's LSTRC. This is the highest level of recognition and means articles receive MeSH indexing.

• "PubMed indexed" = The article appears in PubMed, which could mean it's from a MEDLINE journal, PMC, or publisher-supplied. This is less prestigious than MEDLINE indexing.

• "PMC listed" = The full text of the article is available in the PubMed Central repository. This indicates open access availability but not necessarily MEDLINE indexing.

When evaluating journal quality, always check specifically for MEDLINE indexing status rather than just PubMed presence.

Publishing in a MEDLINE/PubMed-indexed journal is a significant achievement in biomedical research. Follow these steps:

• Select the Right Journal: Search for MEDLINE-indexed journals in your field using the NLM Catalog at www.ncbi.nlm.nih.gov/nlmcatalog. Filter by "Currently indexed in MEDLINE" to find active journals. Consider the journal's scope, audience, Impact Factor (if WoS-indexed), and publication model (open access vs. subscription).

• Follow ICMJE Guidelines: Prepare your manuscript following the International Committee of Medical Journal Editors (ICMJE) Recommendations. These guidelines cover manuscript structure, authorship criteria, conflict of interest disclosure, and ethical standards. Most MEDLINE journals require ICMJE compliance.

• Use Appropriate Reporting Guidelines: Follow the relevant reporting guidelines for your study type: CONSORT for randomized trials, PRISMA for systematic reviews, STROBE for observational studies, STARD for diagnostic accuracy studies, CARE for case reports, or ARRIVE for animal research.

• Ensure Ethical Compliance: Obtain Institutional Review Board (IRB) / Ethics Committee approval for human studies, informed consent from participants, clinical trial registration (e.g., ClinicalTrials.gov) before enrollment for interventional studies, and IACUC approval for animal studies.

• Check Originality: Use plagiarism detection tools like iThenticate to ensure your manuscript is original. Most MEDLINE journals have strict plagiarism policies with similarity thresholds of 15-20% or lower.

• Submit and Navigate Peer Review: Submit through the journal's official portal with a strong cover letter. Biomedical peer review for MEDLINE journals typically takes 4-16 weeks. Address reviewer comments systematically with detailed point-by-point responses.

• Post-Acceptance: After acceptance, your article will be published and indexed in MEDLINE with MeSH subject headings, making it discoverable through PubMed to millions of researchers and healthcare professionals worldwide.

To verify if a journal is genuinely indexed in MEDLINE (not just present in PubMed), use the following methods:

• NLM Catalog: Visit the NLM Catalog at www.ncbi.nlm.nih.gov/nlmcatalog and search for the journal by title or ISSN. Check the "Current Indexing Status" field — it should show "Currently indexed for MEDLINE". This is the most reliable official method.

• List of Serials Indexed for Online Users: NLM publishes the List of Serials Indexed for Online Users (LSI), which contains all journals currently indexed for MEDLINE. This list is updated annually and available on the NLM website.

• PubMed Search: Search for the journal in PubMed. If articles appear with MeSH terms assigned to them, the journal is MEDLINE-indexed. Articles without MeSH terms may be PubMed-only (not MEDLINE).

• Check the [sb] Tag in PubMed: You can use the search query "journal name"[journal] AND medline[sb] in PubMed. If results appear, the journal is indexed in MEDLINE.

• Beware of Misleading Claims: Some journals claim to be "PubMed indexed" or "PubMed listed" but are not actually MEDLINE-indexed. Always verify through the NLM Catalog. Being in PubMed is not the same as being MEDLINE-indexed — MEDLINE is a higher standard with a rigorous evaluation process.

• Check for Discontinued Indexing: Some journals may have been previously indexed in MEDLINE but later deselected. The NLM Catalog shows both current and historical indexing status, so check for the "Currently indexed" designation.