UK Community Advisory Board (UK-CAB)

Clinical trials – a guide for CAB members (page 6)

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  • This picture shows the stages of clinical trials.
  • If a new medicine looks promising in the laboratory, and is safe when tested in animals, a Phase I study in humans is the next step. Phase I trials test the medicine in only a few people (usually healthy volunteers) to learn whether it is safe for humans to take.
  • Phase II studies usually involve more people. The goals of a Phase II study are to assess if the medicine is safe, if it slows down or stops the progression of the disease, and the dose at which the medicine is effective. If the results show the medicine is safe and effective, the researchers conduct a Phase III study. The study sample (the number of people who join) of the Phase III study will be much larger than that of the Phase II study.
  • In Phase III studies, researchers continue to monitor the safety and effectiveness of the medicine. They also observe and record how the new medicine works compared to a medicine that is already known to be safe and effective. For example, A Phase III study might compare a new medicine for TB with an existing medicine.