Health Insurance for 20 year-old | ADHD Information

My son, who is 20, has been dropped from our insurance.  Is there any way we can get them to let us keep him on ours?  He takes 3 medications, hates school after years of bad treatment from both teachers and students, so college is out of the question, at least for now, and is having a hard time finding a job.  So far, he hasn't gotten into any trouble, but if he can't get his meds, and without insurance it would be very expensive for us, I'm afraid of what might happen.  I heard that if your adult child has a disability, he can't be dropped, but is ADHD a disabilty?  It was considered one all through school, but now he seems to be on his own.  After 20 years of keeping him out-of-trouble, I would die if it came down to lack of health insurance.  Any ideas? is there anything in the US that states that if a child has a disability/disorder and require their parents help, that they can stay on as a dependant.

I know for my family I could stay on my parents insurance until I was 21. Now I'm 27 without insurance or a job (although I've been job hunting forever)and it is damn expensive. The cheapests I can get my Adderall is 5 a month. I got that buy going to every pharmacy within 25 miles and asking for there price for the med for someone without insurance. If I hadn't shopped around I would be paying over 0 at the pharmacy down the street.

I lost my job a little less then 2 years ago. At that job I had health insurance so I only paid for my prescribtion every month. When the insurance ran out it was a real shock. Until I find another job I've been picking a different bill to not pay every month so I can afford my meds. Not taking them is not an option for me, especially if I want to find a job. This month the electric bill doesn't get paid, next month will probably be the water or gas bill. This works for now since in my state at least nothing gets turned off unless you don't pay two months in a row. So I'm struggling but making due. Hopefully the job market will open up again soon or else I'm in real trouble.