What are the phases of a clinical drug trial?

Most clinical drug research progresses in an orderly series of steps or phases.

• Phase I trials are studies to evaluate how a new drug should be given, and how safe it is to humans.
  
  
• Phase II trials provide preliminary information about how well the new drug works, and generates more information about its safety and benefits.
  
  
• Phase III trials compare a promising new drug, combination of drugs, or procedure with a current standard of treatment.
  
  
• Phase IV trials include the continuing evaluation that takes place after FDA approval, when the drug is already on the market and available for general use.