Hi, I just thought I would let you know that we have similar problems in our family. I haven't found much of a solution. Ours isn't a joint custody issue, we simply allow my nephew to visit his paternal grandparents on weekends, summers, and holidays to maintain those relationships. They don't keep him on any kind of schedule and they try to talk him out of taking his meds. He comes home an emotional wreck. His first morning is h**l. Since they never see him on days when he has any responsibilities, they don't empathize at all.
I would think it would be different for your ex since he sees him when he has to actually function. Does he not understand that he responds better on a schedule? Would your son need the dosage increase if he did have a more set schedule? Routine helps so much with the meds and with ADHD. I would also think you would have some leverage since this is a medical condition and there are custody issues. If he doesn't want to follow doctor's orders, maybe his custody status could be reconsidered.
Total abdominal hysterectomy at age 26 due to abnormal bleeding. Kept ovaries.