For most generic drugs, they function just as well as name brand drugs, but there are some differences.
The active ingredient is the same. If there is any difference, it is in the other items such as fillers and binders. Fillers are non-active ingredients needed to bulk up the tablet to a manageable size or give a tablet a specific color. Binders hold the ingredients together in a tablet form until the active ingredient is released when the tablet dissolves. Sometimes a person may be allergic to one of the fillers or binders in the generic or brand name drug.
Sometimes the amount of pressure used to compress the loose powder into a tablet is too much. This makes the tablet harder to dissolve and it just takes longer to get into the liquid state before absorption. Sometimes a coating can delay absorption, there by lowering the peak drug level.
Even though the active ingredient is the same, fillers, binders, compression and coatings do affect the more subjective responses any one person might experience.
Does this make any difference? Usually not.