Glossary

Clinical research terms in plain language

Short definitions of words you may see in a study listing or consent document.

Studies and phases

Clinical trial: A research study in people that tests a medical approach, such as a medicine, device or procedure. It follows a written plan.
Interventional study: A study that gives people a treatment or other intervention, as set by the study plan, to see its effects.
Observational study: A study that watches what happens to people over time without assigning them a treatment.
Phase: A step in testing a medicine, from Phase 1 (small group, safety) to Phase 4 (after approval). Some studies have no phase.
Protocol: The written plan for a study: who can join, what will be done, what will be measured and how safety is watched.
Control group: A group that does not receive the treatment being tested, or receives standard care or a placebo, so results can be compared.
Placebo: An inactive substance or treatment that looks like the real one.
Randomization: Assigning people to study groups by chance.
Blinding: Keeping participants, and sometimes the study team, from knowing which treatment a person receives.

Sponsor: The company, university, agency or other group that starts, manages or pays for a study.
CRO: Contract research organization. A company that a sponsor hires to manage parts of a study, such as monitoring sites or handling data.
Investigator: The doctor or other qualified person who conducts a study at a site and is responsible for participants there.
Principal investigator: The lead investigator at a study site.
Study team: The investigator and staff, such as nurses and coordinators, who carry out the study and answer your questions.
Institutional review board (IRB): An independent committee that reviews a study to help protect the rights and safety of participants.

Eligibility criteria: The rules for who can and cannot join a study, such as age, diagnosis or other treatments. A study team decides eligibility, not a website.
Healthy volunteer: A person without a health problem related to the condition being studied who joins a study, for example to help test safety.
Informed consent: The process of learning about a study, asking questions, and agreeing in writing to take part. It continues during the study.
Adverse event: Any unwanted medical problem that happens while someone is in a study, whether or not the treatment caused it.
Withdrawal: Leaving a study before it ends. Participants may do this at any time.

Definitions are written in our own words from the sources below and are general. A study document may use a term slightly differently.