Most if not all addicts have some sort of personality disorder. Whether it be NPD, BPD etc.
It's the chicken or the egg concept are they mentally ill because of the addiction or did they become addicts because of their mental illness.
My opinion, and it's only my opinion, they became addicts because of their mental illness.
I also think many of us humans have some emotional issues and some use subsances to numb, and others use, sex, shopping, drama, codependency etc.
Find me one emotionally healthy human on this planet! There isn't one! We are all a work in progress. I also think many mentally ill people CAN change, though there is little hope for NPD unless they accept they are and work on it. But it's truly engrained in them
There is also healthy narcissism and unhealthy narcissism, depends how much the person hates themselves and needs to keep their false self alive and well.
I used to have a hard time saying addiction was a "disease" ....addiction is NOT a disease, but the underlying mental illness that causes people to become addicts is a disease.
In my opinion, it's healthy to identify the person or persons in your life to better understand yourself. Life is not all about ME ME ME, it's about who you chose to share it with or who you chose to not share it with. Unless of course, you want to live in a hole alone forever!