Just sharing my anecdotal experience after taking Vyvanse for a week.
I haven’t experienced any unusual problems have a small cup of coffee or two in the mornings. My Dr. did inform me that I may experience afternoon headaches in the front of my brain – not so much related to caffeine or meds. She said a small protein rich snack can help. I keep a bag of almonds handy, and eat a few regularly through the day, as well as making sure I stay well hydrated.