By kaw, A generic drug must contain the exact drug as the name brand, but the inactive ingredients can vary. But, when one of my sons had juvenile migraines, his child psychiatrist said that for some reason, a lot of generic psych and neurotropic drugs don’t act the same as name brands.
Inactive ingredients are a factor
Some have different rates of breakdown/absorbtion than original drugs, ie original may have 12 or 24 hr release, steady breakdown, the generic may not
The amount of drug in a dose can vary by a significant percentage enough to cause problems due to lack of quality control on the generic. They know from history and reviewing generics the amount of drug in a pill or dose can vary from the brand name by up to 20% or more sometimes, despite what its labeled as having.