I have a child who was very similar. Here is our story.... He was in foster care (pre my adopting him) starting at 7 mo. He had a very good foster mom. She had to carry him everywhere after age 1 because he banged his head, bit, screamed, hit, etc...would have silly charming moments, said some words in between.... but they treated him behaviorally and he went to Special Education. He started having seizures which often started with those screams. The head banging ended up being intense pain. He had a large brain mass that had grown, was full of blood and was leaking and causing strokes. He also has autism. whether or not that was caused by the brain injury who knows, he does have a predisposition in his bio family as he has at least one confirmed bio brother with autism. It is very likely that there are other things going on with your son and ODD only describes behavior. It does not help define what is going on that is causing the symptoms of opposition and defiance.
Now, that said, from the time he was 2 he was on Clonidine (similar/same class of medication) and it is used for very very young kids in tiny doses ...when they are this aggressive. Often for kids with autism. It is a blood pressure medication that had the effect of calming and helping with aggression and attention (for some kids). He is on it again as a teen and it works beautifully for him. It doesn't for everyone, as you will find....medications are so variable. He was on it from before I adopted him at 2.9 years until he was nearly 5. Then we just managed with a stimulant and an anti seizure medication.
If I were you, and of course this is totally up to how comfortable you feel, I think ODD is a very incomplete picture of what could be triggering this. Because of my son's story I would say if you notice anything that seems odd physically to see a neurologist. (good to clear that area anyway). Then I would seek three complete evaluations. 1. A speech/language pathology evaluation looking at his understanding and use of language and how he uses language for engaging others (he is young, you need someone who understands how very young children play and communicate and most early therapy centers do a good job at this). Of course you need to make sure hearing is ok. At his age you can only get hints as to whether or not he is processing language (like does he need longer time to understand what you say and does he have a harder time when it is noisy around you etc....)
2. An occupational therapy evaluation: check motor and sensory integration function. 3. get a neuropsychological evaluation (neuropsychologist). These are specialized psychologists who look at the wide range of behaviors and symptoms people have and help connect that to how our brains work. They can help give a more specific diagnosis. They take longer to get into than the others so it is good to get the others done first and bring those results so they can put the pieces together.
In the mean time....What is his birth history like?? any difficulties during pregnancy, the birth, illnesses after?? How does he play?? mostly chase types of play (climbing, running, maybe some imitating, etc...) does he do back and forth imaginative play or does he just share the same area/piles of toys and play next to/sort of with other kids?? How does he do when you go from one activity or one place to another? Especially from a preferred to a non preferred activity? How is his eating, is he picky? Does he get more upset in noisy places? Does he have intense fears? Does he look at people when he is communicating with them? Does he like to be touched, if so is it only on HIS terms? Does he rock, shake his hands, do anything like that? (my son loved to sit on a couch or big chair that was fluffy behind and rock to bounce off of it, he likes that deep smashing pressure.
How is his sleep? How is his speech/language, did he talk early? Does he like books? Is he already learning to recognize letters, numbers, words, etc???
Just some questions that allow us to say if our kids were similar to yours and if our stories match at all it can give you some ideas of where to check for help. You will get lots of input and it is all out of care and understanding for how hard this is. And how wonderful our kids are and well worth the effort to help them.
A couple of books that may help What your Explosive Child is Trying to Tell you has specific early childhood ideas (by Douglas Riley) and The Explosive Child by Ross Greene has lots of ideas and there are sections on this board that help adapt it for early childhood.
Welcome to the group! I am glad you found us and hope you can find some comfort and support here. Let us know what you decide and how it works out for you!