Bookmarks Share Print

Glossary of clinical trial terms

Arm assignment
The assignment of a group or subgroup of participants in a clinical trial to receive interventions, or no interventions, as specified in the study protocol.

A procedure (e.g., a blood test, scan, etc.) used to generate data required by the trial.

Background therapy is the current medication that is routinely taken as a standard of care for a particular condition/disease.

A type of clinical trial design where information on which interventions have been assigned to whom is masked from one or more parties, such as the participant or investigator.

Control drug
Drug(s) used in trial to reduce bias, preserve blinding of an investigational drug, and/or to compare to the investigational drug in order to evaluate the comparative effect.

Cross-over trial
A clinical trial where groups of volunteers are administered two or more interventions in a specific order. For example, a “two-by-two” cross-over trial design is where one group receives drug A at the beginning of the trial and then receives drug B for the rest of the trial. In the second group, participants receive drug B first and then drug A. Thus, the term “cross-over” is used to describe the order in which they are assigned; for example drug A and then drug B, or drug B and then drug A. All participants receive both drugs during the study.

Dosing discontinuation
Point/time when a patient volunteer permanently stops taking study drug for any reason; may or may not also be the point/time of premature patient withdrawal.

In a double-blind trial, only the pharmacist knows what study medication a patient is receiving; the doctors, nurses, patients, and other clinical trial staff are not informed.

Early patient withdrawal (premature withdrawal)
Point/time when a patient exits from a trial prior to the planned completion of all investigational/trial drug administration and all assessments (including follow-up).

The point, or time, of a volunteer’s entry into the trial; the point at which informed consent must be obtained (i.e., prior to the start any procedures described in the protocol).

The planned stage of the volunteers’ participation in the trial. Typical epochs are: determination of subject eligibility, wash-out of previous treatments (i.e., a period of time when previous treatments are stopped), exposure of subject to treatment, or the follow-up on subjects after treatment has ended.

A disease, symptom or particular set of circumstances that make a particular test, medication, procedure, or surgery advisable. For a drug, an indication refers to the use of that drug in treating a particular disease.

Informed consent
Informed consent is used by researchers to explain the clinical trial to potential volunteers. Its purpose is to protect the participant. It is used when somebody who is interested in participating first asks about the study and it continues throughout the study, until the study ends. The research team will review the details of the trial with the potential participant and will answer any questions. This information is also written in a document, known as the informed consent form, which is designed to be clear and easy to understand.

If a person decides to enroll in a clinical trial, they will sign the informed consent form to acknowledge that they understand the details of the trial and consent to participating.  The informed consent form is not a contract and the participant can withdraw from the trial at any time, and for any reason

Institutional Review Board (IRB)
An IRB (also known as an independent ethics committee (IEC), ethical review board (ERB) or research ethics board (REB)) is an appropriately constituted group (e.g., including men and women, scientists and non-scientists) that has been formally designated to review and monitor biomedical research involving human subjects.

Investigational drug
The drug whose properties are being evaluated in the trial; this definition is synonymous with “investigational new drug” or “investigational medicinal product.”

Medication number
A unique number on the label of each investigational/trial drug package that is used in a trial to dispense medication. The number is used to track medication that is being used and ensure the drug is supplied in the right quantities to different research centers.

A subdivision of a single protocol into major building blocks. These parts often are independent of each other and have different objectives or different groups of volunteers. For example, a single-dose design and a multiple-dose design may be combined into one protocol (a protocol with two parts) or the same study design could be used with different groups of patients with different severity of a disease.

Categories, defined by the Food and Drug Administration (FDA), for describing the clinical trial of a drug based on the study's characteristics, such as the objective and number of participants. There are four phases:

Phase I trials test an experimental drug, vaccine or device in a small group of people to evaluate safety, identify side effects and determine safe dosages.

Phase II trials involve larger groups of people than Phase I and they are designed to assess the safety and efficacy of an experimental treatment. This phase can last several years.

Phase III trials are usually large studies comparing the experimental drug or vaccine to a placebo or standard treatment, to evaluate efficacy and collect information to allow it to be used safely.

Phase IV trials are performed once a drug has reached the market, to provide additional information about the optimal use of the drug.

Placebos are inactive substances. In a clinical trial a placebo, made to look like the investigational medicine, is sometimes used as a comparator to the actual investigational medicine. This allows the investigators to evaluate whether an investigational medicine provides any effects when compared to a substance with no active ingredients. Placebos versus investigational medicines can also often be administered in addition to current “standard treatment options” for the disease.

Principal Investigator
For the purposes of defining the responsible party, the principal investigator means “the individual who is responsible and accountable for conducting the clinical trial. The principle investigator assumes full responsibility for the evaluation of human subjects, and for the integrity of the research data and results.” In most cases the principal investigator of a trial will be a leading doctor in the disease area being studied. 

The written study plan on which the clinical trial is based. A protocol describes what types of people may or may not participate in the trial; the schedule of tests, procedures, medications, and dosages to be administered; the outcome measures that will be evaluated; and the length of the study.

Randomization number
A unique number assigned to each randomized patient that is used to identify individuals but maintain anonymity, corresponding to a specific study arm assignment.

Run-in period
The elapsed time before a trial starts when no investigational drug is given to trial participants. During this time patients may still receive standard treatments for their disease if these treatments are allowed within the trial period.

Stop trial participation
The point, or time, at which the patient volunteer comes in for a final evaluation visit or when trial/investigational treatment was discontinued (whichever is later).

An individual (either a healthy volunteer or a patient volunteer) whose reactions or responses are studied during a clinical trial.

Subject number
A number assigned to each patient who enrolls into a trial.

Information collected during a clinical trial either from direct or indirect data. For example, one variable might be “weight,” which would then be checked at specified time points throughout the trial.

Wash-out period
The period of time allowed for all of the administered drug to be eliminated from the body.