Hun you're not killing your son by putting him on Ritalin. You're a fantastic mum & you're doing what's best for your little boy. The behaviors he is displaying he can't control & there is no way he wants to behave the way he is so you have to do what is best for him.
There is a little boy at my work with ADHD, he is a beautiful little boy, on Ritalin. When he is not on his medication he swears at the carers, lashes out at the other children, can't focus at all on an activity, is running around from one thing to the next & will repeat things over & over, like kicking the wall, he could stand there and do it for an hr. It breaks my heart to see him like that, he is such a sweetheart & doesn't want to be like this he just can't help it when he hadn't had his medicine. When he has had it he is kind, loving, gives hugs, likes to help out with things, helps the other kids out & has a permanent smile on his face & enjoys being involved in social activities.
You're his mum, don't let anyone tell you what you're doing is killing your son. You're at your wits end by the sound of things and are making an informed decision based on professional medical advice.
Good luck Hun xox