Well...this is  a tough one. You (and others) have been there all his life to remind him and it sounds like you have had the typical rough time with a CAH kid. At some point however, you are not going to be there, and he will have to make the decisions about not just this, but everything else that effects him.

I have CAH and have refused my meds. Fortunately mine is a mild form and I can go without for quite awhile. Your son is now an adult and seems to be saying "NO" possibly to assert his independance or because he just can't take it anymore.

What would you do with an adult in the same situation? Obviously the adult knows the consequences, so telling them what they already know doesn't work.

When I was a youngster and won't go to school or study, my parents didn't get angry. They simply pointed out that I would be the one to repeat the year (not them) and my friends would laugh at me. Well... I went on to University and have two degrees.

Maybe you could try to treat him like an adult (if you haven't already), listen to his reasons (eventhough you maybe horriffied) and possibly work out something with your doctor to meet some terminally ill young adults so he has a concept of death.

Hope this helps!