My friends parents are both in pharma and work at a high level in drug development. We had a conversation about this years ago, and they both told me to never use generic anything.
They said that the way you arrive at synthesizing a drug and the excipients used can have a significant effect on how the end product behaves, even if the chemical structure of the drug is technically the same.
I am not educated on the matter so I can't explain it in detail/scientifically the way they did, and have no way to verify it.
I can say I've noticed differences between pharma/generics/UGL with testosterone a few times, but this could be due to quality control. Other times no difference. I'm using generic GH now with no problems. I've had pharma test cyp from a generic give me significantly lower levels than the name brand. So who knows. I just use name brand pharma when I can for peace of mind.