i found on the fda website under how drugs are developed and approved this i a very great article but way to much to copy on here so i highlighted section 5 and 6
A manufacturer applying for FDA approval of a brand-name drug must conduct a series of animal and in vitro studies evaluating the pharmacology and toxicology of the drug before opening an investigational new-drug application to conduct human clinical studies. Subsequently, adequate, well-controlled clinical studies
are necessary to demonstrate the safe and effective use of the drug in the planned
patient population. In general, these clinical studies include clinical safety, pharmacokinetic, and bioavailability studies in healthy human volunteers (phase I studies); proof-of-concept studies showing the drug may be effective in treating the specific disease (phase IIa studies); dose- ranging studies to define the lowest effective dose (phase IIb studies); and large, well-controlled studies evaluating drug safety and efficacy (phase III studies). The number of clinical studies needed for approval varies by therapeutic indication and availability of other adequate treatments for the disease (6) FDA approval of generic drugs requires the applicant drug company to supply the proposed drug label, CMC information (6), and bioavailability and bioequivalence data for the generic drug. A side-by-side label comparison of the generic and brand- name drugs is required in the application, with any differences in labels annotated and justified.
also later in the article it states this towards the end
The main difference between generic and brand-name drugs is the amount and type of evidence supporting the market application of the respective drug. A brand-name drug is required to demonstrate substantial preclinical and clinical evidence showing safety and efficacy in apatient population. A generic drug does not have to demonstrate this safety or efficacy, as it is assumed the drug will act in a similar manner. However, a generic drug is required to demonstrate bioequivalence to the brand-name drug.