They are not the same drug, reread what I said. You can't be very familiar with pharmacology if you don't understand prodrugs. They turn into almost Adderall, which isn't straight dextroamphetamine. This changes how they effect the body, you can say "essentially the same" all you want, but it's not true when it comes to how they actually impact people. Differing metabolic rates due to naturally different levels of metabolizing enzymes causes prodrugs to have more variance in their peak blood serum levels, it causes later onset of effect and can cause large variance in duration of effect. This can be very helpful or even dangerous for some people. They are not perfectly interchangeable, even if most people find them pretty similar.