What is a clinical trial?
A clinical trial is a research study involving people. Depending on the study, researchers may evaluate medicines, devices, procedures, behavioral approaches, screening methods, or other interventions under a defined protocol.
Common study phases
Phase I
Often focuses on safety, dosage, and how an intervention behaves in the body, usually with a relatively small group.
Phase II
Continues safety evaluation while gathering more information about whether the intervention has the intended effect.
Phase III
Typically involves larger groups and may compare a new approach with an existing standard, placebo, or another study design specified in the protocol.
Phase IV
May occur after an intervention is approved and can examine longer-term effectiveness, safety, or use in broader populations.
Terms you may see
- Protocol: the study plan describing who may participate and what will happen.
- Eligibility criteria: characteristics used to determine who can join.
- Randomization: assignment to study groups by chance in some trials.
- Placebo: an inactive comparison used in certain study designs.
- Blinding: limiting who knows the assigned study group to reduce bias.