Meds can definitely be a part in him being argumentative and having meltdowns. Too high/ow a dose or the wrong med/medcombo can exacerbate behavior instead of mitigate it. My son takes Straterra with Vyvanse and as I understand it Straterra is used to augment the stimulant to help with impulsivity and ocd. In our case iwe saw an improvement when combining the two where Straterra alone did nothing and Vyvanse alone helped with attention but ramped up ocd so the two together were the answer for us. You don’t say how long he’s been taking the Vyvanse but at 11/12 (my son is 12) their bodies start changing, puberty hormones start impacting their behavior, etc so adjustments to meds wouldn’t be uncommon at this age. Good that you’re seeing a specialist – family doctors and regular pediatricians in my experience don’t have the knowledge to manage adhd. Finding the right medication can be a long road so hang in there!