My understanding of Vyvanse is that it uses metabolic mechanisms in order to time the release of the drug which helps to prevent abuse. I'm far from a doctor however.

I’m not sure about vyvanse specifically but for some medications the time release mechanism is the coating. my comment should have been more clear

vyvanse relies heavily on the second pass effect to activate, which is what makes it resistant to abuse. it also means if you don’t make sure to eat lunch the second half of the dose doesn’t kick in until supper and you end up being awake until 4-5am. ask me how i know…