How Would You Counsel Someone Who You Suspect Might Be Demon-Possessed?
My good friend, seminary professor and theologian, Gerry Breshears, has written/compiled three different articles related to this subject. He has done extensive research and has firsthand experience in dealing with demon possession.
Three Models of Deliverance (from demon possessions)
Also, see the article “How should a Christian respond to mental illness?” There are several resources listed there.