Yes, you should avoid Vitamin C and citric acid within an hour of taking stimulant medication. Your best bet would be to work with your doctor or an integrative meds doctor to try to devise a plan of supplements and medication that is safe and effective.
One idea would be to get a B-complex without Vitamin C in it, then take a simple Vitamin C at bedtime (as long as your doctor agrees, of course).
Penny
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism