What symptoms does your son manifest?
Risperdal is an antipsychotic given for many disorders at this point although it was originally intended for schizophrenia. There are other medications that are traditionally used for bipolar. I think you really need to consult a pediatric psychiatrist for decisions revolving around medication----- and there is also a doctor's forum here that may be of more assistence. But that is all so personal to the child ----- only a professional in your area can give you legitimate advice. Good luck.