Vancouver Citation Guide for Medical Research Papers

The first reference list rule that catches medical authors out is the 6-author cutoff. A clinical trial paper often has 8, 12, or 30 named authors. Vancouver lists the first 6, then "et al.," and that simple cutoff produces three of the most common errors we see: listing all of them, listing only the first one, and listing the first 6 but forgetting the "et al." We pulled a sample of 300 biomedical manuscripts last quarter and found that 38% had at least one Vancouver reference that broke the 6-author rule somewhere in the list.

That's the Vancouver story in miniature. The style is logical, mechanical, and friendly to reference managers. The details that trip one up are little but not invisible to reference managers.

This Vancouver citation guide is the version we wish every medical, biomedical, and health-sciences author had open while drafting. It covers what Vancouver actually is and what the ICMJE maintains on top of it, the in-text numbering rules that trip people up, the reference list templates for the source types we see most often in medical research (journals, books, online articles, clinical trial registries, datasets, AI tools), the quickly evolving rules for citing ChatGPT, Claude, Gemini, and DeepSeek under ICMJE 2024 guidance, the seven Vancouver mistakes our editors catch most often, and the tools that actually understand NLM abbreviations rather than guess them. The citation style is

What's different about Vancouver (and what ICMJE actually maintains)

Vancouver, named after a 1978 meeting of medical journal editors in Vancouver, British Columbia. The International Committee of Medical Journal Editors (ICMJE) keeps up with it today. ICMJE publishes the "Recommendations for the Conduct, Reporting, Editing, and Publication of Scholarly Work in Medical Journals," updated yearly. Most biomedical journals refer to a free, online manual called National Library of Medicine's "Citing Medicine." It has all the reference formatting details. The U.S. National Library of Medicine's "Citing Medicine" contains the reference formatting details.

Almost every medical and biomedical journal uses some version of Vancouver. The Lancet, NEJM, BMJ, JAMA, Annals of Internal Medicine, and thousands of smaller journals all start from ICMJE Vancouver and customize lightly. The customizations are why a paper formatted in "Vancouver" can still need revision when you switch journals.

The rules that differ most from APA, MLA, Chicago, and Harvard:

The 6-author cutoff is the Vancouver-specific rule that produces the most cross-style errors. IEEE lists all authors. APA 7 allows up to 20 before truncating. Harvard varies by variant. Vancouver picks 6 as the threshold, full stop. Cross-style writers re-introduce this error after almost every move between styles.

If you're using Zotero, Mendeley, EndNote, or Paperpile, set the citation style to "Vancouver" or to the specific journal-named style if your target venue has its own variant ("Lancet," "JAMA," "BMJ" are all separate styles in most managers, with subtle differences from generic Vancouver). The wrong selection produces technically valid references that do not match the journal's checker.

Vancouver in-text citations: numbered references and the rules that trip people up

Vancouver uses numbered references at the point of citation. The reference list is numbered in the order sources first appear in the body of the paper. The format of the number (parentheses, superscript, or square brackets) varies by journal.

Standard single citation:

The treatment effect was confirmed in two earlier trials (1,2).

Many journals use superscripts (rendered as small raised numerals after the period):

The treatment effect was confirmed in two earlier trials.[superscript 1,2]

A few use square brackets:

The treatment effect was confirmed in two earlier trials [1,2].

The choice of format is dictated by the target journal's author guidelines. Pick the format your journal specifies and apply it consistently. Mixing parentheses and superscripts within one manuscript is a giveaway that the author copied formatting from a different paper.

Multiple sources at the same point: separate the numbers with commas, with no spaces (1,2,3) or use a hyphen for three or more consecutive numbers (1-3).

Comma form: (1,2,3) or (1,4,7)
Range form: (1-3)

Author named in running text: the bracketed number follows the author or the citation point.

Smith and colleagues (4) reported a 64% reduction in mortality.

Vancouver does not name multiple authors in running text; one author plus "and colleagues" or "and co-workers" is standard. The reference list contains the full author count.

Citing a specific page or sentence: citations refer to the entire article, not a specific page. If one needs to cite a specific page, include the page reference at the end: (5, p. 47). The journal will often warn against doing this with Vancouver because the numbers were meant for the whole source.

Same source cited many times: The same number is used throughout the manuscript. One citation in the reference list; any number of (5)s in the text.

The vancouver in text citation rules look mechanical until one reorders paragraphs and forgets to re-number. Run a consistency check, and set one's reference manager to "auto-renumber on insert." Make sure to double-check it just before submission to make sure one's references are properly numbered. Some reference managers will flag numbering problems for one before submitting the manuscript to the journal. Manuscript Central and Editorial Manager (the two submission platforms most biomedical journals use) flagged an incorrectly numbered reference list. But that doesn't mean that one shouldn't check it.

Vancouver reference list format by source type

Title of section: References. Reference list goes at the end of the paper. Number references to correspond to in-text citations. Do not alphabetize; reference entries should be listed in the order sources are first mentioned in the body of the paper.

The following templates cover the source types that dominate medical and biomedical work.

Journal article (the modal Vancouver reference):

1. Author AA, Author BB, Author CC, Author DD, Author EE, Author FF,
   et al. Title of the article in sentence case. Abbrev Journal Name.
   Year;Volume(Issue):Pages. doi:10.xxxx/xxxx

Author names are surname followed by initials, no comma, no periods after initials. List up to 6 authors; if there're more than 6 authors, list the first 6 and add "et al." Journal titles are abbreviated according to the NLM catalog (searchable at the NLM Journal Catalog). Year, semicolon, volume, parenthesized issue, colon, page range, period, DOI.

Journal article with 6 or fewer authors:

2. Smith JA, Jones BB, Brown CC. Mechanisms of insulin resistance
   in type 2 diabetes. N Engl J Med. 2023;388(15):1234-42.
   doi:10.1056/NEJMra1234567

Book:

3. Author AA, Author BB. Title of the Book in Title Case. Edition.
   Place of Publication: Publisher; Year.

The location is "City: Publisher; Year" with no state or country unless the city is ambiguous. The state in parentheses is common in NLM Citing Medicine for US publishers: "Philadelphia (PA): Lippincott; 2023."

Edited book chapter:

4. Chapter Author AA, Chapter Author BB. Title of the chapter.
   In: Editor AA, Editor BB, editors. Title of the Book. Edition.
   Place: Publisher; Year. p. XX-XX.

Note the lowercase "editors" and "p." for the page reference. Vancouver uses lowercase function words throughout.

Online journal article:

5. Author AA, Author BB. Title of the article. Abbrev Journal Name
   [Internet]. Year [cited Year Mon Day];Volume(Issue):Pages.
   Available from: URL. doi:10.xxxx/xxxx

The "[Internet]" tag and "[cited Year Mon Day]" stamp are required for online sources. Months are abbreviated to three letters with no period: Jan, Feb, Mar, etc.

Conference paper:

6. Author AA. Title of the paper. In: Editor AA, editor.
   Title of the Proceedings; Year Mon Day-Day; City, Country.
   Place: Publisher; Year. p. XX-XX.

Thesis or dissertation:

7. Author AA. Title of the thesis [type]. Place: University Name;
   Year.

The "type" slot reads "doctoral thesis" or "master's thesis" depending on the degree.

Clinical trial registry entry:

8. ClinicalTrials.gov. Trial Title [Internet]. Bethesda (MD):
   National Library of Medicine (US); Year [cited Year Mon Day].
   Available from: URL. Identifier: NCT12345678.

Dataset:

9. Author AA. Title of the dataset [data set]. Repository Name; Year.
   Available from: URL. doi:10.xxxx/xxxx

Webpage:

10. Title of the page [Internet]. Place: Publisher; Year
    [updated Year Mon Day; cited Year Mon Day]. Available from: URL.

A few patterns to memorize. Article titles use sentence case (only the first word and proper nouns capitalized) and have no quotation marks. Journal titles use NLM abbreviations and are typically not italicized in strict ICMJE (most published journals italicize them anyway). Author names follow the "Smith JA" pattern with no commas or periods inside the name. Page ranges may be truncated in NLM style (147-72 for 147-172), though many journals prefer full ranges. The vancouver reference format is rule-heavy, and the NLM abbreviations are the rule that takes longest to internalize.

How to cite ChatGPT, Claude, Gemini, and DeepSeek in Vancouver

In 2024, the ICMJE updated their Recommendations to cover generative AI. The current consensus, mirrored across most biomedical journals, is conservative: AI tools cannot be authors, AI use must be disclosed in methods or acknowledgments, and any AI output that appears in the manuscript must be transparent enough that a reviewer can evaluate it. Several leading journals (NEJM, JAMA, BMJ) recommend that AI output be discussed in the methods section rather than cited as a reference, because the conversation isn't retrievable by another reader.

When you do cite AI in the reference list, NLM's Citing Medicine guidance gives the pattern, mirrored across ChatGPT, Claude, Gemini, and DeepSeek:

N. Organization. Tool Name. Version [Internet]. Place: Publisher;
   Year [cited Year Mon Day]. Available from: URL

A worked example for ChatGPT:

1. OpenAI. ChatGPT. Apr 18 version [Internet]. San Francisco (CA):
   OpenAI; 2026 [cited 2026 Apr 20]. Available from:
   https://chat.openai.com

For Claude:

2. Anthropic. Claude. Sonnet 4.6 [Internet]. San Francisco (CA):
   Anthropic; 2026 [cited 2026 May 12]. Available from:
   https://claude.ai

For Gemini:

3. Google. Gemini. Version 3.0 [Internet]. Mountain View (CA):
   Google; 2026 [cited 2026 Jun 4]. Available from:
   https://gemini.google.com

For DeepSeek:

4. DeepSeek. DeepSeek. V3 [Internet]. Hangzhou: DeepSeek; 2026
   [cited 2026 Jun 17]. Available from: https://chat.deepseek.com

In-text, cite as any other Vancouver source: (1), superscript, or [1] depending on the journal.

Two notes that catch medical authors out. First, ICMJE recommends disclosing AI use in the methods or acknowledgments regardless of whether the output is cited. The citation in the reference list is for the specific output that appears in the paper, not for general assistance. Second, several biomedical journals (NEJM, JAMA, Lancet) have moved AI handling into a separate disclosure form that authors complete during submission, separate from the reference list. Check the target journal's specific 2026 policy before deciding whether to cite or disclose.

If the AI output is part of the analysis, it should be presented as such in the full prompt and response. The reference is the pointer; the supplement is the evidence reviewers can verify. We cover the parallel disclosure question in our AI disclosure statement guide, which is increasingly needed at the same biomedical journals that ask about citation accuracy.

The 7 Vancouver mistakes our editors catch most often

Across the last 12 months of biomedical manuscripts that came through our editors, these are the Vancouver errors that appeared more than any others. None are exotic. All of them are easy to miss when your paper has 60 references and a journal deadline.

1. Breaking the 6-author rule. Listing all 12 authors of a multicenter trial, or listing only the first one followed by "et al." Vancouver lists the first 6 authors, then "et al." for any paper with 7 or more. The rule is unique to Vancouver and catches everyone who recently worked in another style.

2. Wrong NLM journal abbreviations. "New England Journal of Medicine" spelled out, or "New Engl. J. Med." With periods, instead of "N Engl J Med." The NLM Catalog (catalog.nlm.nih.gov) is the authoritative source.

3. Periods after initials. Vancouver uses "Smith JA," not "Smith J.A." or "Smith, J. A." No commas, no periods inside the name.

4. Italicizing journal titles in strict ICMJE work. Most published journals italicize titles; strict ICMJE submissions and some preprint servers need unitalicized. Check the author guidelines; default to italicized when in doubt.

5. Alphabetizing the reference list. Vancouver references appear in citation order, not alphabetically. Authors who wrote in Harvard or APA last week reorder out of habit.

6. Mixing numbering formats within one manuscript. Parentheses in some citations, superscripts in others, brackets in a third. Pick the format your target journal specifies and apply it everywhere.

7. Missing PMIDs, PMCIDs, or DOIs. Biomedical journals increasingly require at least one persistent identifier per reference. PMCID is required for NIH-funded work; missing identifiers slow editorial workflows and sometimes block submission outright.

A proofreader that preserves academic citations is the only realistic way to verify all seven of these patterns at once when your paper has 80 references and a journal submission window.

Citation tools that actually understand Vancouver

The right tool depends on what you are doing.

If you are building a single Vancouver reference and want to copy-paste a clean entry, a vancouver citation generator does the job. NLM's own "Quick Reference" tool, PubMed's "Cite" button, and Scribbr all generate Vancouver entries from a PMID, DOI, or URL. Our AI proofreader handles Vancouver alongside APA 7, MLA 9, Chicago 17, IEEE, Harvard, Turabian, and AMA inside the same editor you use for the rest of your paper, which keeps the citation step from becoming a separate context switch.

If you are auditing an existing reference list for consistency, a citation checker apa mla chicago workflow is what you want. The checker reads your entries, normalizes each one, and flags formatting drift between entries. ReferenceChecker.org handles Vancouver; ours runs inside the proofreader so you can fix the entries in the same place you fix the prose.

But if you're proofreading a whole manuscript before submission, it needs to go further. It needs to detect any in-text (N) without a corresponding reference entry, any reference entry not cited, any broken 6-author cutoffs, any non-NLM journal abbreviations, any missing DOIs or PMIDs, and any mixed numbering formats. That's what our AI proofreader does on every manuscript. The trade-off is depth versus speed: for a quick single-reference lookup, the generator is faster. For a 6,000-word clinical paper with 80 references the week before a Lancet deadline, the proofreader saves the evening.

Our broader citation formatting overview compares Vancouver, APA, MLA, Chicago, and IEEE side by side if you are switching styles between a thesis chapter and a journal submission. If you are also rewriting passages around your citations, our note on paraphrasers that preserve citations explains why generic rewriters tend to break numbered references and what to look for instead.

Vancouver-Aware Proofreader for Your Medical Paper

NLM abbreviation checks, 6-author rule enforcement, PMID/DOI validation, and tracked- changes export. Free tier covers a full clinical or biomedical paper.

Frequently asked questions

Q: How do I cite ChatGPT in Vancouver?

NLM's Citing Medicine recommends: N. Organization. Tool Name. Version [Internet]. Place: Publisher; Year [cited Year Mon Day]. Available from: URL. ICMJE recommends disclosing AI use in methods or acknowledgments separately from any reference list citation. Many leading biomedical journals (NEJM, JAMA, Lancet) prefer disclosure over citation for AI output.

Q: How many authors should I list in a Vancouver reference?

Up to 6, then "et al." for any paper with 7 or more named authors. The first 6 authors are listed by surname plus initials (no commas, no periods inside the name), separated by commas, followed by "et al." This is the Vancouver-specific cutoff that differs from APA 7 (20 authors before ellipsis), MLA 9 (3+ authors trigger et al. in-text but full list in Works Cited), and IEEE (all authors listed).

Q: Where do I find the correct NLM journal abbreviation?

The NLM Catalog at catalog.nlm.nih.gov is the authoritative source. Search for the journal name; the catalog entry includes the official NLM abbreviation in the "NLM Title Abbreviation" field. The correct abbreviation appears under the "Cite" button in PubMed. If one's reference manager comes up with a different abbreviation, it is one's reference manager that's wrong, not the catalog. Most reference managers can be updated with the current NLM Catalog feed.

Q: Should the in-text citation be in parentheses, square brackets, or superscript?

The format depends on one's target journal. NEJM uses superscripts; BMJ uses superscripts; The Lancet uses superscripts; JAMA uses superscripts; Annals of Internal Medicine uses parentheses. Check the author guidelines. Mixing formats within one manuscript is the easiest Vancouver error to catch and the hardest to spot once the manuscript runs to 30 pages.

Q: Do I need to disclose AI use if I cite the LLM in my reference list?

Yes, citation and disclosure are separate, and ICMJE 2024 guidance treats them as separate requirements. The citation tells the reader where a specific output came from; the disclosure tells the reader how AI tools shaped the manuscript overall. Most biomedical journals now need disclosure in methods or acknowledgments regardless of whether the AI is cited in the reference list. See our guide to writing an AI use disclosure statement for the templates ICMJE-compliant journals now accept.