FDA requirements for drug approval

I was wondering if anyone knows generally what criteria that the FDA uses when it comes to approving drugs. Is it something like "It needs to work for X percentage of people" or is it something like "It just needs to work better than a sugar pill"?

All new drugs need to be proven both "safe and effective" by clincal analysis. Since no drug is absolutely safe (there is always the chance of an adverse reaction) the FDA does a risk/benefit analysis. If the benefits outweigh the risks of a drug the FDA declares the drug safe enough to approve. (I can elaborate on the approval process but it would make this a serious FRAT.) It isn't just a matter of it working in a certain percentage of the population. The drug's value must outweigh the risks of its use. Not only must the drug be shown to be effective but it must also be shown to be worth while in relation to its side effects.