Clinical Trial Phases

This section describes phases I, II, III, and IV in the trial process. 

Treatments that are tested in clinical treatment trials typically go through several phases of study, in a step-by-step fashion. Each phase asks different questions about the potential treatment.  If a phase of a treatment trial is successful, then the researchers will go on to test the treatment in the next phase of research. If a phase of a treatment trial shows that the treatment is dangerous or does not provide benefit, the treatment is generally not used in any further trials
In Phase I trials, researchers test an experimental drug or treatment for the first time in humans by using a small group of research participants (usually 20-80) to test the treatment’s safety, begin to understand how the treatment effects the body, find a safe dosage range, and identify side effects.

In Phase II trials, researchers give the experimental treatment to a larger group of people to see how well it works, identify common short-term side effects, and further test its safety.

In Phase III trials, researchers give the treatment to large groups of people to confirm that it works, look for and describe side effects, compare it to other available treatments, and collect information that will allow the treatment to be used safely.  The results from this phase are used to make recommendations to healthcare providers about the use of the treatment in all patients.

In Phase IV trials, researchers look at a therapy after it has been offered to the public to get more information, for example about the drug's risks, benefits, and optimal use.

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When the study is done

After a clinical trial is completed, the researchers look carefully at the data collected during the trial before making decisions about the meaning of the results. After a phase I or II trial, the researchers decide whether to move to the next phase, or to stop testing the drug or intervention because it was not safe or effective. When a phase III trial is done, the researchers look at the data and decide whether the results have medical importance.
The results of clinical trials are often published in peer-reviewed, scientific journals. Peer review is a process by which experts review the report before it is published to make sure the analysis and conclusions are sound. If the results are particularly important, they may be featured by the media and discussed at scientific meetings and by patient advocacy groups before they are published. Once a new approach has been proven safe and effective in a clinical trial, it may become standard practice or standard of care. (Standard practice/standard of care refers to a currently accepted and widely used approach.)