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Glossary of Clinical Trial Terms

ADVERSE REACTION: (Adverse Event):

Also known as side effects, adverse

reactions include any undesired actions or effects of the experimental drug or treatment.

Experimental treatments must be evaluated for both immediate and long-term side



A drug, device or biologic must be approved by a country’s regulatory

agency before it can be marketed. The approval process involves several steps

including pre-clinical (animal) studies, clinical trials for safety and efficacy, filing of a New

Drug Application (NDA) in the United States or Marketing Authorization Application

(MAA) in Europe by the manufacturer, regulatory agency review of the application, and

agency approval/rejection of application.


Any of the treatment groups in a clinical trial. Most randomized trials have two

“arms,” but some have three “arms,” or even more.


Baseline information is gathered at the beginning of a study from which

variations found in the study are measured. Baseline can also be described as a known

value or quantity with which an unknown is compared when measured or assessed.

Safety and efficacy of a drug are often determined by monitoring changes from the

baseline values.


When a point of view prevents impartial

judgment on issues relating to the subject

of that point of view. In clinical studies, bias is controlled by blinding and randomization.


A clinical trial is “blinded” if the participants are

unaware on whether they are in the experiment

al or control arm of the study. Blinding

may also be extended to the investigators so that their patient observations are less

likely to be biased by their awareness of the treatment the patient is receiving.


A scientific study that compares a group of people with a

disease (such as leukemia) to a similar gr

oup of people without that disease. This type

of study compares the levels of exposure (for example, radiation or chemical) each

group had before appearance of the disease.