Hi there

I can see where you would be very concerned about this particular behavior.  It isn't good for your son or for the cats he cannot take care of properly.  Are you saying that he is presently not on any medication?  And...I assume he is living alone?  What about the cats now...does he still have a large number of cats? 

I am also wondering if he may have obsessive compulsive disorder...as the hoarding behavior may go along with this.  OCD can also be a co-morbid condition of ADHD.

Have you discussed this problem with his doctor?

This type of behavior is usually done by women.  Here is a NY Daily News article about cat hoarding.  The thing is...I am sure your son probably feels he is actually rescuing the cats but without thinking that he cannot take care of a lot of cats.

It really is imperative that a way is found to help your son to cease this behavior not only for his sake but for the animals.

Let us know more about the situation and maybe we can research some help or options for you to explore.