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Clinical Trial Terminology

These definitions will help you understand the various stages of research, and the steps that a drug must go through before it is approved for use by the Food and Drug Administration (FDA).

Clinical Trial

A clinical trial is a research study designed to test the safety and/or effectiveness of drugs, devices or treatments in humans.

Clinical trials can usually be divided into four categories or "phases" that a drug must undergo before it can be approved by the FDA.

The four phases must be completed in order, and positive results must be obtained before moving to the next phase.

Phase I

This is the first of four stages of clinical trials in humans. In Phase I studies, the experimental drug is usually given to a small group (20-80) of healthy volunteers.

The purpose of a Phase I study is to gather information on safety.

Phase II

A Phase II trial involves a larger number of participants (100-300) who usually have the disease for which the experimental drug is being tested.

The purpose of this phase is to gather additional information on safety and effectiveness. Often these studies are "blinded" - neither the patients nor the researchers know who is getting the study drug.

About one-third of experimental drugs successfully complete both phase 1 and phase 2 studies.

Phase III

The third stage of testing involves large numbers of patients (1000-3000) who have the disease for which the experimental drug is being tested.

This stage of testing usually compares the experimental drug to the current approved treatment for the disease.

An application to approve the experimental drug can be submitted after this stage of testing.

Phase IV

This stage is performed after the drug has been approved by the FDA.

In Phase IV, studies are done to compare the drug to a competitor, examine the long-term effects of the drug, or look at the drug in new types of patients.

What is a Placebo?

A placebo is an inactive pill, liquid or powder designed to resemble the treatment being tested.

It is used as a control to measure any psychological effects testing may present.

Most studies compare a placebo with the treatment drug to assess its effectiveness.