Talk to your dr, Tell him whats happening. Ask him if there's a different medication he can take. Maybe Ritalin is not right for him. Sometimes kids have side effects on one medication and have less or none on another. I personally hate the thought of medication. I think my son is ADHD. He is 9 now and I know I have to test him and put him on MEds. School is a big struggle for him. It's a difficult decidtion to medicate and it's also equally difficult not to medicate.
Pull him off Ritalin and try Concerta and try it in lower to higher doses. Ritalin at a higher dose was hard on my 10 yr old. He was diagnosed with ODD when he was 5 and it takes time. We got over hurdles by therapy, putting him in extracurrricular activites. He is now on Concerta 54mg in the morning and takes 5mg of Ritalin in the afternoon.
Concerta has been great, no side effects or anything. We had bad reactions with vyvvanse with my 6yr old - as in hallucinations big time. They are both on Concerta actually.
keep in mind the medication is not for ODD - there is no medication for that. They give the medication for ADD or ADHD, which mine have. It only helps them focus.
Another issue could be the dose is to low and its wearing off to soon. Ask your doctor about that based on your childs weight and age.
I am very grateful that I've met a child pshycologist and psychiatrist that actually beleive that medication of children in general should take place only after all behavior management techniques proved as not working....They actually only reccomend it in very severe cases. Main problem with meds is that they "help to concentrate", but they do not teach to concentrate. Your child still is not able to concentrate - without meds. Meds mess with his growing brain function. There may be underlying anxiety problems etc. Meds only fight the symptoms, but do not work on a problem. I will only medicate my child when I will admit that nothing else works with him (and it is not true - it already works) if he is endangering himself/others. What is that your child doing that makes you think that he needs medication in such an early age? Especially if you do not see difference in behavior anyway? There is no magic pill to "fix" behavioral problems. I understand medicating if school is struggle, but, cmon - for a 4 year old? That psychiatrist that I reffered to earlier said that long-term effects of medications on young children is unknown.
If pre-school cannot deal with his behaviors - you may be able to get him into early childhood developmental program; good programs use all kinds of techniques to actually teach children compliance.
Most children do not come to this world, knowing how to act; some learn from their environment, and some need more instruction, time, and structure. US is way, way overmedicated. Hence people lost ability to work through their mental issues. Give him a chance to work through things (with most importanly your and also professional help). Get an advice from behavioral consultant, get a behaviour management plant. Consistency and systematic approach make miracles happen:) If I were you, I would get a second opinion from another doctor. Good luck