You may want to get your doctor to write your ex husband a letter explaining the issue and especially explaining the dangers of having a child go off and on this type of medication. Instead of letting the emotion (or perceived emotion) get a hold of the situation, let a third party communicate the facts--especially the dangers.

File a petition to alter the terms of your custody arrangement. I'm assuming you have a court-ordered or court-sanctioned custody agreement following your divorce? You can always go back to the Judge to change the terms of the agreement. File a petition and lay out the reasons you either need to have him more often or your ex can only have supervised visits, or however you feel you can best remedy the situation (YOU, not your ex, cause clearly you can't count on him to follow direction). Include a note or letter from your doctor stating that your son has to take the medication, how frequently, and why he cannot be allowed to self-administer. I can't guarantee it will work, but at least it's another option.

im working filing a petition but it also will cost me 3000 by the time I file and get a lawyer to help. I have all the letters from the doctors. guess its going to be the first part of the year until I can get things for money together.

Take video of your son with you on his medicine & record when he gets home and exactly how different he is. Remember unfortunately with courts it's what you can prove not what you say

I don't know how old your son is but maybee if you got a pill box labeled for your ex it would be easier for him to give meds in morning and night. Sometimes men just want the easiest way and if it is 90% done for them then maybe he will follow giving directions. But you can also get a watch with a timer for your son to wear and set alarms and teach him to say time for my meds when the alarms go off. If he has an ipod he could use that too.