[refurb]

I think the OP is overstating by calling generic drug "shit". However, generic drugs do not have to be identical to the branded versions. As measured by pharmacokinetics, they need to fall within 80% to 125% of the branded version. So there is some variation. This webpage does a nice job explaining.[1]

The generic drugs also do not have to have the same excipients (inactive materials used to make the final drug product like a pill or capsule). Normally this doesn't matter, but if you have an allergy to an excipient, the branded might be the only one you can take.

Finally, there have been issues with some generic drugs, namely generic Wellbutrin. The FDA asked for bioequivalence data on some dosage forms, but not the 300 mg pill. That pill released drug much faster than the branded and patients had some nasty side effects as a result. I've also heard the same with some generic anti-epileptics. Epilepsy is a disease where drug levels need to be very tightly controlled.

[1]http://www.pharmacytimes.com/contributor/timothy-o-shea/2016...