Exorcism
In Catholic Christianity, exorcisms are performed in the name of Jesus Christ. A distinction is made between a formal exorcism, which can only be conducted by a priest during a baptism or with the permission of a bishop, and "prayers of deliverance" which can be said by anyone.
The Catholic rite for a formal exorcism, called a "Major Exorcism", is given in Section 11 of the Rituale Romanum. The Ritual lists guidelines for conducting an exorcism, and for determining when a formal exorcism is required. Priests are instructed to carefully determine that the nature of the affliction is not actually a psychological or physical illness before proceeding.
Gabriele Amorth
Amorth was also interviewed for the second episode of "True Horror with Anthony Head", presented by Anthony Head. He explained he would never perform an exorcism based solely on someone's claims of possession; always directs people to psychiatrists and doctors first, and that when he sees someone is not possessed but the person still insists, he replies: "You have no devil. If you have a problem, talk to a good vet."