Concerta kept losing effectiveness for my son too. We tried adding lots of different medications to sustain efficacy. Ammantadine helped for a couple years, but built up in his system and caused side effects like severe anxiety.
There are two types of stimulants: amphetamine (Adderall, Vyvanse, Evekeo…) and methylphenidate (Ritalin, Concerta, Quillivant…). Almost everyone does well on one type or the other, but not both. It may be that your child would do better on an amphetamine-based stimulant. Or simply on a different methylphenidate. Every medication is somewhat different, even if they’re the same type.
ADDitude Community Moderator, Parenting ADHD Trainer & Author, Mom to teen w/ ADHD, LDs, and autism