When my difficult child 2 was first rx'd Risperdal for his agressive behavior in the 3rd grade, I had a similar reaction as yours. I read the words "schizophrenia" and "antipsychotic" and panicked. Turns out, that medication really did help him for a good long while. In his case, much of the aggressive behaviors and lousy impulse control (despite the ADHD stimulants he was on), were likely prodromal symptoms of the bipolar disorder he is now confirmed to have some four years later. I'm not suggesting that's the course your child will take by any stretch. That's just the path we've been on.
My point is that you should not worry too much about the labeling of the primary diagnoses for which a medication is typically rx'd. With many mental health problems, drugs are used off-label from their originally FDA-approved use. It happens a lot that way in medicine. A drug is developed for one disorder/disease, and by happy coincidence another use is found for it. It just takes time for the practical uses to catch up with the legal labeling. That's where doctors rely on their years of experience, research studies and trial and error.
As far as side effects, it did cause a big jump in my son's appetite, and consequently some weight gain. However, the stimulant medications he was on seemed to balance out the appetite issue to a degree. He put on a few extra pounds, but it was nothing that an active lifestyle couldn't address. He did have sedation from it, so dosing at bedtime is usually the way to go to minimize that effect. I hope it works for your son!