But with any addict if there are no consequences for their actions their behavior will never change. We are basically enabling him to continue to live this way - his parents are continuing to enable him to live this way by giving him a place to live, stuff to eat.
Intervention isn't making anyone do anything. It is confronting the person with your concerns, laying out the consequences if they do not get help and they have to make a decision with what they want to do.
