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Types of Clinical Trials


There are several types of clinical trials.  Each trial has a goal and a question that it seeks to answer such as the examples below:

Treatment trials

  • What types of new treatments can help people who have a disease or condition?
  • What is the most-effective treatment for people who have a specific disease or condition?

Prevention trials

  • What approaches can prevent people from developing diseases?

Early-detection/screening trials

  • What are new ways of finding disease in people before they have any symptoms?

Diagnostic trials

  • How can new tests or procedures identify disease symptoms more accurately and at an earlier stage?

Quality-of-life/supportive care/survivorship trials

  • What kinds of new approaches can improve the comfort and quality of life of people who are being treated or have been treated for a disease? 

What Are The Phases of Clinical Trials?

Most clinical research that involves the testing of a new drug progresses in an orderly series of steps, called phases. This allows researchers to ask and answer questions in a way that results in reliable information about the drug and protects the patients. Most clinical trials are classified into one of three phases:

  • Phase I trials: These first studies in people evaluate how a new drug should be given (by mouth, injected into the blood, or injected into the muscle), how often, and what dose is safe. A Phase I trial usually enrolls only a small number of patients, sometimes as few as a dozen.

  • Phase II trials: A Phase II trial continues to test the safety of the drug, and begins to evaluate how well the new drug works. Phase II studies usually focus on a particular type of disease.

  • Phase III trials: Phase III trials focus on learning how a new treatment compares with standard, or the most widely accepted, treatment. Researchers want to learn whether the new treatment is better than, the same as, or worse than the standard treatment. In Phase III trials, participants have an equal chance to be assigned to 1 of 2 or more groups (also called “arms”). In a study with 2 groups:
    • 1 group gets the standard treatment and is called the “control group,” in trials that are not for chronic disease like cancer or diabetes; the control group may be given a placebo. 
    • The other group gets the new treatment being tested and is called the “investigational group.”


Phase III trials may involve thousands of people and a trial may have multiple sites in different cities and different countries around the world.

In addition, after a treatment has been approved and is being marketed, the drug's maker may study it further in a Phase IV trial. The purpose of phase IV trials is to evaluate the side effects, risks, and benefits of a drug over a longer period of time and in a larger number of people than in phase III clinical trials. Thousands of people are involved in a phase IV trial.