Generics can have from 20 to 25% difference from "brand" drugs. And, as my Dr. says, "You never hear of the drug companies putting 20 to 25% MORE in the generics!" Through a painful journey of over a year, he determined that I cannot take generic drugs, especially pain meds. He tells me that this sensitivity is not uncommon, even though the FDA, and everyone else says that there is no difference, Not true---at least for me.