I have not worked w/ 4 yr olds, but have worked with 5 - 10!
I know that I am not a parent of a child on Risperdone, but I taught kiddos that had/have emotional impairments/behavioral disorders at the Elem. level (K-5).
We had a few kiddos that Risperdone did wonders for. Honestly- night and day. It did not zone them out, rather reduced the intensity of anger/rages/etc. Soemtimes it took some dosage tweeking, but the school I worked at was flexible and would help parents look for side-effects as well as keep a log of behaviors to chart improvements/worsening symptoms.
I can not imagine as a parent the anxiety you feel to try such a med on a young kiddo (and feel isolating if you dont know anyone else that is going through the same thing and/or are not supportive of your situation), but as a teacher - I have seen it work well for some kids age 5-7 and again the older kids (as they go through puberty) it helps them focus/contain emotions long enough to learn some coping mechanisms and be able to absorb academic and social skills as well.
Is there a local support group or other parents you can talk with to ease your anxiety? Families that have children that may be facing the same behavior patterns as your DS may have ideas, personal stories, or just be able to provide much needed support.
Often, there is a lull between ages 7-13/14 where a certain maturity (depending on the developmental age of the kid vs chronological age) allows some coping skills to develop and a few kids go med free or are able to take something else....some kids go back on it (or another med) when they are dealing with puberty related hormonal moods. But at age 4-6, sometimes the natural bubbling emotions of a preschooler are simply overwhelming and using medication is a well-thought out solution to enable them to stop the 'react- act' cycle and start to learn some proactive, preventation and self-soothing techniques. It can be scary for a family and for the kiddo to rage : finding a way (through meds, talk therapy, play therapy, ABA, etc) to help the child feel more control and empowered over their own emotions is huge. Under the care of a good Dr, use what methods you can and know you are doing the best for your child and your family with the information you have the current situation.
Also, know if it does not work--- try something else, then you will know what you have tried and can take a new path. If it does help, know that it is the best choice right now for your DS and your family.
*HUGS* I hope you continue to see improvement and have a successful visit with the psychiatrist.