Clinical trial terms, explained
Trial listings are written for researchers. These are the terms you’ll run into most, in plain language — 62 of them.
Progress comes only from learning — terms and concepts, never from what you do with any one trial. All the terms
Adverse event
Any medical problem that happens during a study, whether or not the treatment caused it.
Arm
One of the groups in a study, each receiving something different.
Baseline
Your starting measurements, taken before treatment begins.
Behavioural (as an intervention type)
A programme, therapy, education, or lifestyle approach being studied.
Biological (as an intervention type)
A treatment made from or by living systems — such as antibodies, vaccines, or cell-based therapies.
Biomarker
Something measurable in the body used as a signal of what is happening.
Cohort
A group of participants sharing a characteristic, followed together.
Combination product (as an intervention type)
A product that combines two categories — for example a drug delivered by a device.
Confidence interval
A range showing how precisely a result has been pinned down.
Control group
The group a new treatment is measured against.
Crossover
Each participant receives both treatments in turn, in a set order.
Data Safety Monitoring Board (DSMB)
An independent group that reviews safety data while a study is running.
Device (as an intervention type)
A physical instrument, implant, app or piece of equipment being studied.
Diagnostic test (as an intervention type)
A scan, blood test, or other test being studied for how well it detects or measures something.
Dietary supplement (as an intervention type)
A vitamin, mineral, or other supplement being studied.
Dose escalation
Later groups receive higher amounts than earlier ones, increased step by step.
Double-blind
Neither you nor the study team knows which group you are in.
Drug (as an intervention type)
A medicine — a chemical or small-molecule treatment — given as the thing being studied.
Early Phase 1
A very small, very early study of how the body handles a treatment.
Eligibility criteria
The full list of requirements for taking part in a study.
Endpoint
The specific thing a study measures to answer its question.
Enrolment
The number of participants a study plans to include, or has included.
Exclusion criteria
The things that would prevent someone from taking part.
Follow-up
Continued check-ins after the treatment part is finished.
Genetic (as an intervention type)
A gene-based treatment — such as gene transfer or gene editing — being studied.
Healthy volunteer
Someone without the condition being studied who takes part anyway.
Inclusion criteria
The things you must have or be for a study to consider you.
Informed consent
The process of being told what taking part involves, then choosing freely.
Intention-to-treat
Everyone is analysed in the group they were assigned to, even if they stopped.
Interventional study
A study where participants are given something to see what happens.
Maximum tolerated dose
The highest amount that can be given before side effects become unacceptable.
Observational study
A study that watches what happens without assigning any treatment.
Open-label
Everyone knows which treatment is being given — nothing is hidden.
Other (as an intervention type)
An intervention the registry did not place in another category.
Pharmacokinetics
The study of how the body absorbs, distributes, and clears a treatment.
Phase 1
The earliest stage of human testing, in a small group, focused on safety.
Phase 2
A middle-stage study looking at what a treatment does and watching for side effects.
Phase 3
A large study comparing a treatment against the current standard.
Phase 4
A study of a treatment that is already approved and in use.
Placebo
A dummy treatment with no active medicine, used for comparison.
Placebo-controlled
The study compares the treatment against a dummy treatment.
Primary endpoint
The single main question the study is designed to answer.
Principal investigator
The doctor or researcher responsible for running the study at a site.
Procedure (as an intervention type)
A surgery, technique or clinical procedure being studied.
Protocol
The detailed plan a study must follow.
Radiation (as an intervention type)
A form of radiotherapy or radiation-based treatment being studied.
Randomised
Which group you go into is decided by chance, not by you or your doctor.
Recruiting
The study is currently looking for participants.
Research Ethics Board (REB)
The independent committee that must approve a study before it can run.
Run-in period
A short trial period before the study proper begins.
Screening
The checks done before joining, to see whether a study fits.
Secondary endpoint
Additional things measured alongside the main question.
Serious adverse event
An adverse event meeting a formal severity threshold, such as requiring hospital admission.
Sham procedure
A procedure made to feel like the real one, without the active step.
Side effect
An unwanted effect thought to be caused by the treatment itself.
Single-blind
One side — usually the participant — does not know which treatment is which.
Sponsor
The organisation responsible for the study overall.
Standard of care
The treatment normally given for a condition outside a study.
Statistical significance
A measure of how likely a result could have arisen by chance alone.
Stratification
Splitting participants into subgroups first, so groups stay balanced.
Trial site
A hospital or clinic where a study is actually run.
Washout period
A gap with no treatment, so the previous one clears your system.
These explain how clinical research works. They are not medical advice, and they don’t describe any specific condition or treatment. Your care team is the right place for questions about your own situation.