Probably somewhere in the area of a week before they are back to their “normal” or even less, because unless I am mistaken this is not a drug that needs weaning. It flushes out of your system in like 2 days at max, sometimes less. If you’re going to do meds with your child, do yourself a favor and find someone who will do a GeneSight test for you. That test is a simple swab of the mouth and they test his DNA against a whole battery of medications (not just ADHD meds) and they will tell you exactly what kind of meds will work with him and what won’t. If he’s on Concerta that’s a methyphenidate based drug. That means he won’t respond well to Ritalin, Focalin or likely any methyphenidate drug. Try an amphetamine based drug like Vyvanse or one of the non-stimulants instead. There are basically three classes of drugs to treat ADHD, methyphenidate, amphetamines or non-stimulants and you already know which one doesn’t work for him now.