Choosing to participate in a research study (clinical trial) is an important personal decision. The following glossary of terms provides detailed information about research studies. In addition, it is often helpful to talk to a physician, family members, or friends about deciding to join a trial. After identifying some trial options, the next step is to contact the study research staff and ask questions about specific trials.

Glossary of Terms

The following glossary was prepared to help the consumer become familiar with many of the common terms used in clinical trials.


An unwanted effect caused by the administration of drugs. Onset may be sudden or develop over time. See Side Effects.

Glossary Sources (we have made minor changes to this copy):

AIDSinfo: Glossary of HIV/AIDS-Related Terms 4th Edition.
CenterWatch, Inc. Patient Resources: Glossary.
ECRI (formerly the Emergency Care Research Institute).
Eli Lilly and Company: Lilly Clinical Trials Glossary. Inc: ClinicalTrials: A-Z Glossary.
National Cancer Institute: Dictionary.