What Causes Aggressive Behaviour On Withdrawal From Ritalin?

my nephew has been put in my care he has been diagnosed with arid since 6yrs old he s now 14 the drs are prescribing him quick release rittalin at school only he s been suspended for 8 days and doesn t take it at home so he s only had his meds twice in two weeks also he doesn t take it on weekends which he really needs but he used to be on slow release tabs but they ve changed it like this this boy is an angel on his meds but off it he s aggressive and just flat out he doesn t sleep much at all which is having an impact on him and my family s and when I tell him off he tells me he can t stop cos he needs his meds allso the pediatrician had him on catapress at night to sleep can u please give me advice I m sitting here at drs now and would like a second apinnon is it healthy for this boy to take these meds only in school hours