I have just read an very interesting article by Odette Nightsky on the subject of Exorcism and Mental Illness. Odette is a trained Shaman and works with people that hear voices. It is a very rounded article , well written with pertinent information and advice. Well worth a read. You can see it here on the Intervoice website
This is a sensitive subject. Often people are told they are delusional and ignored when they talk of such things. I am of the opinion it is better to address the topic. Explore it in detail, demystify it and therefore take away the fear it produces. Instead looking for what may help, solutions and empowerment. Odette covers this nicely.