This can often be explained by formulation differences. Pharma companies often times learn formulation tricks about their drug that they keep proprietary that can significantly affect pharmacodynamics.There is a strange phenomenon in the Rx world where *sometimes* name brand drugs are better or worse for people than the generics. I don't know if it's placebo or what because if the drug and dose are the same, it shouldn't be different, but a lot of people swear it is.
Most common example of this I've seen is Synthroid vs Levothyroxine. For some reason there are a ton of people who can only take one or the other without getting negative side effects. Placebo is a helluva a drug though so it's also possible that the doctor or pharmacy telling someone "you're taking the cheaper stuff" could contribute to that.
