Drug Approval Process:
a)    Phase I:  Drug company can test the drug on 20-30 people to test the drug’s toxicity.  These people don’t have the disease that the drug may be useful for.  See if the drug is safe.
b)    Phase II: Test the efficacy of the drug.  Tests people with the disease to see what effects the drug has on the disease.
c)    Phase III: Most of the action occurs here.  Clinical trials are held to test the scientific validity.  The largest number of patients are tested here to determine whether the drug is more effective than the placebo or if it is more effective for a disease than an existing drug.
(1)    A key to getting the FDA to approve the clinical trial, is to have an IRB–an institutional review board.  Trials have to be approved by this board.  FDA will not approve study unless the study has been approved by the IRB.
(2)    Up until recently, the process ended here.  The FDA left it up to the company to notify doctors of the product, etc.  It is possible that after the drug is distributed to a larger population, side effects would arise that were not seen with the smaller class of patients.  So a fourth phase developed.
d)    Phase IV: Post-market surveillance.  The FDA continues to watch the use of the drug.  Some drugs have been pulled off the market by the FDA or even voluntarily by the manufacturer.