Clinical trial words, explained
The phases of a trial and the words you meet in registries, in plain language.
The phases of a trial
| Phase | How many people | What it asks |
|---|---|---|
| Early Phase 1 | About 10 to 15 people | Does the medicine reach its target in the body? A very small dose, for a short time. |
| Phase 1 | About 20 to 80 people | Is it safe, and what dose can people take? Often the first test in people. |
| Phase 2 | About 100 to 300 patients | Does it do anything against the disease? What are the side effects? |
| Phase 3 | Hundreds to thousands of patients | Is it better than the standard treatment? Groups are usually compared at random. |
| Phase 4 | Many patients, after approval | What happens in everyday use, over a longer time? |
Words
- Clinical trial
- A research study in people that tests a new treatment, a new use of an old one, or a new way to find or prevent a disease.
- Trial registry
- A public list of clinical trials, such as ClinicalTrials.gov or the EU Clinical Trials Information System (CTIS). Every serious trial is in one.
- Registry number
- The ID of a trial in a registry, for example NCT01234567 or 2024-512345-12-00. With it you can check the trial yourself.
- Recruiting
- The trial is looking for participants now. "Not yet recruiting" means it will start soon.
- Inclusion and exclusion criteria
- The rules on who can take part, for example age, earlier treatments or other illnesses. Only the trial team can say whether a person meets them.
- Randomised
- Participants are put into groups by chance, so the groups can be compared fairly.
- Placebo
- A dummy treatment with no active ingredient. In cancer trials it is usually given on top of standard treatment, not instead of it.
- Control group
- The group that gets the usual treatment (or a placebo), to compare with the group that gets the new one.
- Standard treatment
- The treatment doctors normally give for a disease, based on the best evidence so far.
- Sponsor
- The company, university or hospital that runs and pays for the trial.
- Informed consent
- Before joining, the team explains the trial in writing and in person. You sign only if you agree, and you can leave at any time.
- Case report
- A description of what happened to one patient or a few. It cannot show whether a treatment works.
- Observational study
- Researchers watch what happens without deciding the treatment. It can show links, but not cause and effect.
- Systematic review
- A careful summary of all good studies on one question, following set rules.
- Meta-analysis
- A systematic review that also pools the numbers of several studies.
- Guideline
- Advice for doctors written by expert groups, based on the evidence, on how to treat a disease.
- Lab and animal studies
- Tests on cells or animals before any test in people. Most of these never become treatments.
- Healthy volunteer
- A person without the disease who takes part in a trial, often in Phase 1, to check safety.
- Washout period
- The time you must wait between two trials, so the first one does not affect the second.
- Second opinion
- Asking another specialist to look at your diagnosis and treatment plan. It is common and usually welcome.
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