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Phase and Purpose   Sample Size   Length of Study   Questions Researchers Aim to Answer
I. Assess the safety of a drug   20-100 health volunteers or people with the disease/condition   Several months  
  • How it works in the body?
  • What are the side effects associated with increased dosage?
  • Might the IMP work in patients?
II. Test the efficacy of a drug   Up to several hundred people with the disease/condition   Several months to 2 years  
  • Is the IMP safe in patients?
  • Does the IMP seem to work in patients?
III. Efficacy and monitoring of adverse reactions   300 to 3000 volunteers with the disease/condition   1 to 4 years  
  • Is the IMP really safe in patients?
  • Does the IMP work in patients?
IV. Safety and efficacy   Several thousand volunteers with the disease/condition   After the FDA approval during the Post-Market Safety Monitoring  
  • How safe is the new medicine?
  • Does the medicine work in the real world?