What an NCT number is, and how to check a study

Section 01

What the number is

When a study is registered on the main public trial registry it is issued an identifier: the letters NCT followed by eight digits, such as NCT02210780. That number never changes and never gets reused. It appears in journal papers, on product packaging, in press releases and in the small print of advertising claims.[1][2]

Other registries exist — the European one, the Chinese one, several national ones — and the World Health Organization runs a search that spans many of them. But NCT numbers are the ones you will meet most often in dermatology.[5][1]

Section 02

Looking one up in under a minute

• Search the number itself on the registry site, or add it to a web search. The official record is normally the first result.[1]
• Read the Sponsor field. It tells you who paid, and whether the maker of the product also ran the study.[1][3]
• Read Arms and Interventions. This shows what the treatment was actually compared against — placebo, nothing, or a real alternative.[1]
• Read Primary Outcome Measures. This is the single thing the study was designed to answer, and the timepoint it was measured at.[1][2]
• Check Study Results. Either results are posted or they are not, and the difference is the whole ballgame.[3][4]

Section 03

The three fields that decide whether a claim holds

The comparator tells you how hard the test was. A cream that beat a plain base cream has cleared a low bar. A cream that beat the standard prescription treatment has cleared a high one. Most advertising quotes the first kind and phrases it like the second.[1][2]

The primary outcome tells you what was really measured, which is often narrower than the marketing suggests. "Improves skin texture" in an advertisement can trace back to a primary outcome of change in a photographic roughness score at week 12, assessed by one grader. That is a genuine result and a much smaller claim.[1][4]

The results status tells you whether anyone ever reported what happened. Studies can complete and stay silent for years. In our snapshot of 3,745 skin studies, 2,557 have completed and 1,074 have posted results, so silence is close to a coin flip.[4][3]

Section 04

What a record cannot tell you

The registry records plans and postings, not quality. It cannot tell you whether blinding held, whether the graders were consistent, or whether the people enrolled resemble you. Those questions need the published paper, and often the paper does not exist.[1][3]

It is also blind to everything unregistered. Cosmetic products can be sold on consumer perception surveys with no registered trial anywhere, which is why a search returning nothing does not mean a product is untested — it means it was not tested this way.[4][2]

Section 05

A worked habit

Next time a product page cites a study, look for a number. If there is no NCT number and no journal citation, the claim is unverifiable by design and you can stop there. If there is one, thirty seconds in the registry will tell you the comparator and the outcome, which is usually enough to know whether the claim is fair.[1][2]

Our condition pages do this at scale, listing what has been registered for acne, eczema, psoriasis, rosacea and melasma, including which treatments were never compared against each other. The individual study pages carry the same fields laid out in plain language.[4]