Well, lisdexamfetaine is interesting because of how it is absorbed. It is basically novel in the sense that it doesn't enter your bloodstream until it is fully digested by your stomach.
I know people that take a large dose of vyvanse and literally don't feel ANYTHING for 3 hours, and then it peaks.
I know people that take a large dose of vyvanse and it speeds them up for 2 + DAYS AT A TIME.
Me? I take a good dose, it peaks in 1 and a half hours, euphoric for 3 hours after that, followed by a mild/next-to-nothing crash and then I'm perfectly fine. This drug affects people differently than any I have ever seen.....it could be that you just don't digest it right.