Taking 40mg vyvanse (lisdexamfetamine) and i feel dazed and confused. why is that?

That's not really a: High dose, as about 1/3 of it is the active ingredient, adderall, but it may be high for you, or just the wrong med. Onset of action of vyvanse (lisdexamfetamine) is ~ 2 hrs. & it lasts 12-14 hrs. Tell your prescribing physician your symptoms & what time of day or night they occur. Also, list all other medications, herbs etc., you're taking, to rule out a drug interaction. Together you'll find the right med & dose.