Peptide basics
The eleven characters that settle most arguments about peptides
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An NCT number is the unique identifier ClinicalTrials.gov assigns to a registered study. It looks like NCT followed by eight digits.
Every registered trial has one, and it is issued before the trial starts — not after the results are known.
Typing it into clinicaltrials.gov brings up who ran the study, who could take part, what was measured, and often the results.
If someone cites a study and cannot give you an NCT number or a published paper, there may be no study to cite.
This page explains what a trial registration number is and how to use one. It is a guide to checking claims, not advice about any compound, and contains no dose, schedule or route.
What the number is
ClinicalTrials.gov assigns each registered study a National Clinical Trial number: the letters NCT followed by eight digits. It identifies that one study permanently and uniquely.1
The crucial property is timing. The number is issued when the trial is registered, which for most applicable trials must happen before the first participant is enrolled. So the record exists before anyone knows how the trial turned out.2
Why registration before results matters
A trial that declares in advance what it will measure cannot quietly change the question afterwards. If the registered primary outcome and the published headline differ, that is visible to anyone who looks.2
That is the entire point of the registry, and it is why a registration number carries more weight than a citation to a paper alone. The paper is written after the fact; the registration is not.2
What you can see in about a minute
- Who sponsored it, and who ran it.
- How many people took part, and who was eligible to.
- What phase it was, and whether it was randomised and masked.
- What the pre-specified primary outcome was.
- Start and completion dates, and often the posted results.13
STEP 1 is a good record to practise on. It shows 1,961 participants, a phase 3 randomised quadruple-masked design, a start date of 4 June 2018, and a full baseline characteristics table including the sex split.3
How to use it against a claim
The question is short: which trial, and what is its NCT number. A compound with human evidence produces one immediately. A compound without produces a link to a laboratory paper, a review article, or nothing.1
Common questions
Do all trials worldwide have an NCT number?
No. Other countries run their own registries with their own formats. ClinicalTrials.gov is the largest and the one most commonly cited, but a trial registered elsewhere is still registered.
What if the record has no results posted?
Common, and not necessarily a problem — results posting has its own deadlines and many trials publish in journals instead. The registration itself still tells you what was planned.
Can a registration be edited after the fact?
Records are updated, and the history of changes is public on each record. That history is worth looking at when a primary outcome appears to have moved.
Sources
- RegulatoryClinicalTrials.gov — how to read a study recordU.S. National Library of Medicine, 2026clinicaltrials.gov/study-basics/learn-about-studies ↗↩ Back to text
- RegulatoryFDAAA 801 and the Final Rule — trial registration and results reportingU.S. National Library of Medicine, 2025clinicaltrials.gov/policy/fdaaa-801-final-rule ↗↩ Back to text
- Primary studySTEP 1 (NCT03548935) — example registry recordClinicalTrials.gov, U.S. National Library of Medicine, 2021clinicaltrials.gov/study/NCT03548935 ↗↩ Back to text