There have been a few examples where the FDA received complaints, looked at the data and asked the generic manufacturer to rest test/reformulate their drug since it wasn't therapeutically equivalent.
The best example is generic Wellbutrin[1]. Many patients complained of side-effects from generics that they didn't experience with the brand-name drug. The FDA did testing and realized that the generic Wellbutrin extended-release resulted in much high blood concentrations than the branded version. The generics in questions were withdrawn from the market.
The interesting thing is that to get approval for an "AB-rated" (therapeutically equivalent) generic drug, you don't have to be identical. The FDA only requires that the generic drug deliver 80-125% of the drug the branded drug does[2]. Normally that range is fine, but for some drugs (antiepileptics are a good example) the differences can produced a less than equivalent therapeutic outcome.
Problematic generics seem to come up often about extended release formulations when hanging around ADHD communities. Judging from this latest one I remember, it takes a big push for the FDA to start looking into it and ask questions:
As consumers, we don't really have much of a way to test for placebo effects or when generics are actually subpar other than complaining until someone listens... so... it's a bit of a chicken/egg problem.
I think that's my question, as an individual, you can't say that one is more effective than the other because, as an individual, you can't account for the placebo effect. Personally, if it works, it works, placebo or otherwise.
If you search online, you can find isolated regulatory incidents, patient anecdotes, and even statements by doctors that they prefer patients not switching brands when something works for them. Beyond that, I'm not sure what is really known, or how you would go about studying this phenomenon in a scientific fashion.
Even if it is a placebo, if two medications that are supposedly the same cause different effects on me, e.g. one has much more manageable side effects than the other, then why shouldn't I take the one that makes my life better?
The best example is generic Wellbutrin[1]. Many patients complained of side-effects from generics that they didn't experience with the brand-name drug. The FDA did testing and realized that the generic Wellbutrin extended-release resulted in much high blood concentrations than the branded version. The generics in questions were withdrawn from the market.
The interesting thing is that to get approval for an "AB-rated" (therapeutically equivalent) generic drug, you don't have to be identical. The FDA only requires that the generic drug deliver 80-125% of the drug the branded drug does[2]. Normally that range is fine, but for some drugs (antiepileptics are a good example) the differences can produced a less than equivalent therapeutic outcome.
[1]http://www.fda.gov/Drugs/DrugSafety/PostmarketDrugSafetyInfo...
[2]http://www.nature.com/clpt/journal/v94/n4/full/clpt2013104a....