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Different Types of Clinical Trials

for Veterans and the Public

Are there different types of clinical trials?

There are four different types of clinical trials: Phase I, Phase II, Phase III, and Phase IV.

Phase I

  • is the first time they have tried the drug in people
  • tests for the drug's safety and helps find the right dose
  • may ask for frequent tests or a stay in the hospital to check for safety and effectiveness
  • lasts a fairly short time
  • has a small number of patient volunteers

Phase II

  • happens when early studies show that the drug may work well to fight HIV
  • tests for safety and effective dose level
  • lasts longer than Phase I trials
  • tries to find out what kind of side effects people may get with this medicine
  • has several hundred patients

Phase III

  • happens if the drug worked well in Phase I and II
  • compares standard treatments (medicines that you can already get by prescription) or sugar pills (placebos) with the new medicine
  • may last longer than Phases I and II
  • looks for ways to reduce the side effects and improve the quality of your life while you are taking the medicine
  • is the last phase of study before a drug is sent to the FDA for consideration for approval
  • has many patients (sometimes thousands)

Phase IV

  • happens when the drug is already available by prescription
  • happens less often than other phases
  • checks other safety issues and long-term side effects
  • may be used to check higher or lower amounts (or doses) of the medicine