A preprint makes a research manuscript public before journal peer review is complete. A peer-reviewed paper has passed through a journal’s review process. The useful distinction is the scrutiny applied to the exact version you are reading, not a guarantee that one version is wrong or the other is true.
NIH describes preprints as complete public drafts, typically unreviewed, that enable faster sharing and feedback. It recommends identifying their status, version and persistent identifier when citing them. NIH guidance on preprints.
What peer review adds
ICMJE describes peer review as expert assessment of a submitted manuscript. It can improve reporting and inform an editor’s decision. Journals differ in which article types they review, their review procedures and their requirements for data access or independent analysis. Check the policy for the particular article, not just the journal’s name. ICMJE peer-review responsibilities.
The practical implication is that a review label should not be treated as proof of independent replication or a complete audit of the data. It also cannot resolve a mismatch between a study’s population, research material or outcome and the claim someone wants it to support.
Find the exact version
Keep the preprint’s title, authors, identifier, posting date and version number together. Look for a link to a journal article, then compare the documents before replacing the citation. ICMJE recommends clearly labeling cited preprints and using the subsequent journal article when appropriate. It also places responsibility on authors to link preprints to later versions. ICMJE guidance on preprints.
PubMed inclusion alone does not establish peer review: NLM’s NIH Preprint Pilot includes labeled preprints in PubMed and PMC. NLM links identified journal versions, retains earlier preprint versions and marks linked preprints as updated in PubMed. Search by title, author and identifier if a link is missing. NLM preprint and version guidance.
A version comparison worksheet
Use these editorial questions to decide whether your summary still matches its source:
- Participants or samples: Did the number analyzed change? Were exclusions added or explained?
- Outcome and timing: Is the headline result the same measurement at the same time point?
- Analysis: Are the comparison, statistical model, estimate and uncertainty unchanged?
- Interpretation: Did a causal claim become an association, or a firm conclusion become tentative?
- Transparency: Did the protocol, funding, conflicts, data availability or publication-status notices change?
Fictional example: a preprint describes an apparent improvement in 40 participants; the journal article explains exclusions and analyzes 34. Copying the first version’s sample size beside the later version’s estimate would produce a combination that neither document reports. Preserve the version-specific numbers and explain the change. If the reason is unclear, retain that uncertainty.
Two documents are not two independent studies
Before counting a preprint and its journal article as separate evidence, establish whether they describe the same participants and experiment. ICMJE warns that duplicate reports can lead to double-counting and distorted evidence summaries. A later document may add information without adding an independent replication. ICMJE overlapping-publication guidance.
A useful source note is: “This summary uses [identifier and version date]. The earlier preprint reports the same study and is not counted as a second experiment.” Only make that statement after matching the records.
Continue reading
Publication status is one part of appraisal. Use How to Read a Research Study for the methods and results, or return to Research Evidence Guides.
Review and corrections
Sources checked October 1, 2026. This AI-assisted educational summary was checked against the linked official guidance. No independent scientific or clinical specialist review is claimed. It is not medical advice or evidence that a catalog product matches a study material. Report a source discrepancy through Contact Us.