How can I help my childs severe Adult Defiant Disorder?

I've had him on Prozac, and Adderall, he's 8 now and has been on his meds since he was 6... but he still throws fits to anyone in authority position who tries to tell him what to do, my therapist says he's just very independent but has severe symptoms of Adult Defian Disorder, i'm at my wits end, he is always crying in the store, etc.