Clinical Trial Glossary

Clinical trials have a language of their own. If you are considering joining 1 of these studies, it helps to understand the common terms doctors and researchers use when talking about clinical trials. Here are some of the terms you may hear if you decide to join a trial.¹

Adverse event: An undesirable side effect that affects a person during, and sometimes after, a clinical trial. The adverse event may or may not be caused by the treatment being studied.^1,2

Arm: A certain group of people in the study. Each arm of a study may get a specific treatment, or no treatment, so that their results can be compared.¹

Baseline: Information collected at the beginning of a study on each person. This may include things like age, gender, weight, race, and test results.^1,2

Clinical trial: A medical research study in which doctors and researchers compare new treatments and/or tests to existing treatments and/or tests to see which works better. New drugs, devices, surgical techniques, lab tests, imaging techniques, vaccines, diet changes, exercise methods, educational interventions, and counseling approaches are tested this way.^1,2

Controlled trial: A type of study that compares a new treatment to another standard treatment or no treatment. The group of participants getting the standard treatment or no treatment (a placebo) is called a control group.^1,2

Double-blind trial: A type of study in which, typically, neither the doctors/researchers nor the participants know which study group each participant is assigned. This is done to avoid any bias in the results. It is considered the strictest form of clinical trial.^1,2

Exclusion criteria: Things that prevent a person from joining a clinical trial. This could be many factors, such as age, weight, gender, treatments tried before, or certain health conditions.^1,2

FDA: The US Food and Drug Administration. The FDA is the government agency that approves new treatments to be sold in the United States.^1,2

Inclusion criteria: Reasons why a person can join a clinical trial. Things that qualify a person to join a study may include age, sex, type and stage of disease, or treatments tried before. Inclusion criteria also may be called eligibility criteria.^1,2

Informed consent: The process of making sure that a person joining a clinical trial understands the potential risks and benefits of that study. Informed consent also includes making sure the person understands what they will need to do to join the study and that they can stop participating in the study at any time. An informed consent form outlines all of this information.^1,2

Intervention: The treatment or test being studied. This may be a new drug, device, surgery, lab test, imaging technique, vaccine, diet change, exercise routine, or type of education or counseling. It can also be something else completely.^1,2

Institutional Review Board (IRB): An independent group that reviews the details of a study before it starts and can continue to monitor while it is performed. This is done to protect the rights, safety, and well-being of the people who join the study. An IRB also may be called an Independent Ethics Committee (IEC).^1,2

Investigator: One of the researchers carrying out the study.^1,2

NCT number: A unique number given to each clinical trial that is registered on ClinicalTrials.gov. This is 1 way to find a study you want to learn more about.¹

Phase 1, Early: A clinical trial stage used to gather basic information before Phase 1 begins. Humans may take what is known as a microdose of a new drug at this stage. Phase 1, Early was once known as Phase 0.¹

Phase 1: A stage in which a small group of volunteers takes a drug or tests a new device. Doctors and researchers then study the most common and serious side effects, how the drug is processed in the body, and what a safe dose is. The group of volunteers may include a little as 10 to 20 people or as many as 100 people.^1,2

Phase 2: A stage that looks closer at how well the new treatment works on a slightly larger group of people with the disease/condition being studied. This helps doctors and researchers learn more about the safety and effectiveness of the new treatment.^1,2

Phase 3: The stage in which several hundred to several thousand people may be trying the new treatment. The new treatment may be compared to standard forms of treatment or other treatments being studied. Researchers continue to collect information about safety and how well the new treatment works. This is the last step before a new treatment is sent to the FDA for approval to be sold in the United States^1,2

Phase 4: The stage after the FDA approves a treatment for sale in the United States. Researchers continue to track information about its safety and how well it works. This long-term phase includes the largest number of people because the drug or device is being sold on the open market.^1,2

Open-label trial: A type of study in which the doctors, researchers, and participants all know what treatment is being tested and who is receiving it. This compares to a single-blind test, in which typically only the participants do not know, or a double-blind test, in which typically neither the doctors/researchers nor the participants know.^1,2

Placebo: A pill, powder, liquid, device, or method designed to look the same as the treatment being studied. A placebo does not contain active ingredients or involve the treatment method being studied, and it has no treatment value. A placebo may be used as a study comparison to see how well a new treatment works.^1,2

Principal investigator: The researcher (often a doctor) who leads the study and is responsible for the accuracy and standards of the study.^1,2

Protocol: A plan that outlines everything about the clinical trial. This includes what is being studied, how the study is organized, who can join, and how success or failure will be measured.^1,2