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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 life while 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 (doses) of the medicine