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What is a clinical trial?

Clinical trials are scientific studies conducted to find better ways to prevent, screen for, diagnose, or treat disease. These clinical trials may also show which medical approaches work best for certain illnesses or groups of people.

The purpose of a clinical trial is to answer scientific questions. Therefore, these studies follow strict, scientific standards that protect patients and help produce reliable clinical trial results. Clinical trials are an important stage in a long and careful research and development process. The process often begins in a laboratory, where scientists first develop and test new ideas.

Every clinical trial has a protocol or study plan that describes what will be done during the clinical trial, how the clinical trial will be conducted, and why each part of the clinical trial is necessary. The protocol or study plan also includes guidelines, called eligibility criteria, for who can and cannot participate in the clinical trial.

Common eligibility criteria may include:

  • Having a certain type or stage of disease
  • Having received (or not having received) a certain kind of therapy in the past
  • Being in a certain age group
  • Medical history
  • Current health status

Criteria such as these help to reduce the medical differences among people taking part in the clinical trial so that researchers can be more certain that the results are due to the drug, vaccine or device being tested and not to another reason.

In addition, because some people who want to take part in a clinical trial have health problems, outside of the disease being studied, that could be affected by the drug, vaccine or device being evaluated, anyone interested in joining a clinical trial will receive medical tests to confirm their eligibility.