Maybe it was the generic version of Ritalin? The law of the land in the US is there can be a plus or minus of 20% of bioavailability of the active ingredient! FDA still uses the plus-or-minus-twenty percent test to determine blood serum bioavailability (i.e., the amount of active ingredient in the blood over a period of time has to come within plus-or-minus twenty percent of that which is observed when the innovatorís drug is ingested.