This is an antipsychotic drug used mainly to treat schizophrenia. Did the Dr. diagnose schiphrenia or is he using the drug off label? Has a psychiatrist prescribed this for him or just a pediatrician or family doctor.
I am a clinical child and family psychology and child development major and working towards getting my license. I am also a member of the American Psychological Society. I really try to get parents to see a psychologist or psychiatrist (they prescribe the meds) instead of family Dr.s for things like this. The rate at which family Drs. are prescribing these medications really concerns me because I have seen many children have bad side effect from medications and good results from therapy without putting these toxins in their developing bodies.
If you are seeing a psychiatrist who put him on the medication, great, if not please get a 2nd opinion from a psychologist/psychiatrist who is well versed in these disorders. I think of it like this, would you go see a dentist for a problem with your toes? No you'd see a podiatrist (foot Dr).
You really need to see a specialist if you aren't already. Drugs alone rarely work, there is a much more successful treatment rate when medication and therapy are used in conjunction with each other.