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Understanding Clinical Trial Phases

Clinical trials are an important part of developing new treatments yet many patients do not understand the process.

Whether you’ve taken a medication today to manage a chronic disease or simply to keep a headache at bay, you know that medical innovations have the power to change lives. But these breakthroughs don’t just happen. Developing new medicines is a lengthy and complex process, relying heavily on volunteer participation to evaluate potential therapies for safety and effectiveness in clinical studies. Without the patients who volunteer to participate in clinical trials, the development of new medicines would not be possible.

Clinical trials are conducted in phases that accomplish different purposes.

Below is a simple explanation of the different stages in development of new treatments to help patients better understand the research process.

  • Observational study. This early phase allows researchers to better understand the natural progression of the disease they are studying. While experimental drugs are not typically provided during observational studies, participants are often able to continue taking existing medications prescribed by their own physicians.
  • Phase 1 trial. Before new medications are approved for human patients, researchers give the experimental drugs to a small group of healthy volunteers. Researchers determine appropriate dosage, and test for safety and side effects.
  • Phase 2 trial. Once an experimental drug is deemed safe for patients, it is administered to a small group of patients to see if it improves health outcomes for the condition being studied and to continue to evaluate safety.
  • Phase 3 trial. Once data demonstrates an experimental treatment is both safe and effective, a larger group of patients are given the drug. Researchers continue to evaluate the safety and determine if the new drug is more or less effective than current treatments.
  • Phase 4 trial. After the new treatment is marketed to patients, researchers continue to assess the drug’s safety and efficacy.


Additional Resources:
ASF Active and Completed Clinical Trials page
National Institutes of Health
Myths and Facts About Clinical Trials