Surprise he is on Meds

My step son's mother surprised us with new medication for him for ADHD. He has currently been on it for about a week. She already knows his father is dead set against it and they have legal joint custody in NY.The issues she claims to have with him we have not seen while he is with us. Yes, he is very active but what 7 year boy is not. Has anyone gone thru this? We will be talking to our lawyer within the next week.