The FDA currently trusts independent organizations to test drugs produced by pharmaceutical companies that are used by the American people.The FDA checks the results these organizations produce but, not to sound paranoid, these results can be fudged so as to make the drug pass examination. I say that because the organizations are chosen by the drug companies and there is nothing to stop them from "financing" these organizations to get more positive results.
This article I am going to link is able to articulate what I am trying to get across better and also provides some specific examples, so I ask you to please read it too.
http://www.searcylaw.com/do-you-know/dyk-fda-approval/
Here is the link to what the FDA has to say about this.
http://www.fda.gov/drugs/developmentapprovalprocess/d