Not medical advice. This website is not medical advice, a diagnosis, a match to a trial, or a recommendation to join a study. Listings are plain-English rewrites of public ClinicalTrials.gov records. Whether a site is still enrolling, and whether you qualify, can only be confirmed by the study team and your clinician. Source registry: ClinicalTrials.gov. Editorial rules: methodology.
PlainTrials

Vocabulary · reviewed 2026-08-17

A glossary for ClinicalTrials.gov

Short definitions of the words that show up on registry cards. These are reading aids, not legal or medical definitions. For how we rewrite records, see methodology.

NCT number
The unique ClinicalTrials.gov identifier for a study (NCT followed by eight digits). Quote it when you contact a site.
Recruiting
The sponsor has posted that the study is looking for participants. It is not a live count of open slots at every hospital.
Inclusion criteria
Protocol rules that describe who the study wants to enroll (diagnosis, age, labs, prior treatment).
Exclusion criteria
Protocol rules that usually prevent enrollment (other diseases, medicines, pregnancy, recent procedures).
IRB / ethics board
An institutional review board (or equivalent ethics committee) that reviews the protocol and consent materials. PlainTrials is not an IRB.
Phase 1
Usually the first tests in people, focused on safety, dose, and how the body handles the product. Small groups. Not designed to prove a cure.
Phase 2
Looks for a signal that the approach may help, and continues to watch side effects, in a larger but still limited group.
Phase 3
Larger comparison, often against standard care or placebo, used in decisions about whether to seek approval. Not a guarantee of approval.
Phase 4
After approval: new questions about other uses, longer follow-up, or everyday practice.
Placebo
A dummy treatment used so researchers can compare against the investigational product. Not used in every trial.
Randomization
A chance process assigns participants to groups so investigators do not hand-pick who gets which arm.
Blinding (masking)
Keeping assignment hidden from the participant, the clinicians, or both, to reduce biased reporting.
Open-label
Assignments are known. Common in some oncology and device studies.
Standard of care
The usual accepted treatment for a condition in that setting. A trial may compare a new approach with standard care instead of placebo.
Study arm
A group in the protocol (for example experimental vs control). You are assigned to an arm; you do not design it.
Endpoint / outcome
What the study measures to answer its question (survival, symptom score, a lab, a scan). Primary outcome is the main one listed on the registry.
Principal investigator (PI)
The lead researcher at a site or for the whole study. Day-to-day questions often go to a coordinator.
Study coordinator
Staff who schedule visits, collect data, and are often the public contact on ClinicalTrials.gov.
Protocol
The detailed rulebook for the study. The registry record is a public summary, not the full protocol.
Screening
Tests and reviews that check whether you match eligibility before the study intervention starts. Screening can take weeks.
Washout
A required pause after stopping a prior medicine so it does not confuse the study. Ask whether stopping anything is safe for you — only your clinicians can say.
Adverse event (AE)
An unwanted medical occurrence during the study, whether or not it is caused by the product. Sites are required to record them.
Serious adverse event (SAE)
An AE that results in death, is life-threatening, requires hospitalization, or meets other regulatory definitions of serious.
DSMB / safety committee
An independent group that may review safety data while a trial is running and can recommend stopping or changing the study.
Biomarker
A measurable signal (gene, protein, scan) used to select participants or track the disease. A required biomarker is an eligibility rule, not a marketing slogan.
Companion diagnostic
A test used to decide whether a targeted therapy study (or later, a labeled drug) applies to a tumor or disease subtype.
Expanded access (compassionate use)
A separate pathway that is not the same as enrolling in the trial. If a record mentions it, read that section on ClinicalTrials.gov; most NCT interventional records are not expanded-access programs.
Observational study
Researchers measure what happens without assigning the experimental treatment as the intervention.
Interventional study
The protocol assigns a drug, device, procedure, or program to participants.
Healthy volunteer
A participant enrolled without the disease under study, usually in early safety research.
Enrollment number
The registry EnrollmentCount is a planned or reported headcount for the whole study, not a promise of a local opening.
Site / location
A hospital or clinic listed on the record. Listing ≠ current opening.
CRO
A contract research organization hired by a sponsor to help run the trial. Not your clinician.
Good Clinical Practice (GCP)
International quality standard for designing and running trials that involve humans.
IND
Investigational New Drug application in the US, a regulatory file that allows certain clinical investigations of a drug. You will not see the IND number as a patient-facing ID; you will see the NCT number.
FDA
US Food and Drug Administration. Phase labels on drug studies follow common FDA/ICH usage. An NCT listing is not an FDA approval of the product for you.
ICH
International Council for Harmonisation — the source of many shared trial definitions, including phase language.
Primary completion date
When the last participant is examined for the primary outcome, as posted by the sponsor. Dates slip. They are not appointments for you.
Has results
ClinicalTrials.gov flag that the sponsor posted a results module. Many recruiting studies will not have results yet because the study is still running.
Brief summary
The sponsor’s short public description. PlainTrials’ in-plain-English field is grounded in this text plus other public fields.
Intervention
What the study assigns or evaluates: a drug name, device, procedure, or behavioral program listed on the registry.
Condition
The disease or problem the study lists. One NCT number can list several related condition strings.
YMYL
“Your Money or Your Life” — Google’s label for topics (including health) where thin or invented advice can cause harm. PlainTrials answers that with source links, disclaimers, and a named method, not with treatment rankings.