Duloxetine
"I switched from the brand name Cymbalta to the generic version.  After 4 weeks I felt like it wasnt working.  My old symptoms were returning with a vengeance.  I did some research about how generics become approved. Apparently, how fast a drug is absorbed, the extent to which it is absorbed and then leaves the body is calculated and compared to the brand name.  Using this calculation, when the Generic Version falls within 80% to 125% of its Brand Name counterpart then it is considered a bioequivalent (meaning the Generic Version can be officially made-available as a cheaper alternative to the Brand Name version).  So, they are not identical but rather fall within a range of bioequivalent acceptance.  For me, the generic was not effective."