Exorcism in the Catholic Church
According to the Vatican guidelines issued in 1999, “the person who claims to be possessed must be evaluated by doctors to rule out a mental or physical illness.” Most reported cases do not require an exorcism because twentieth-century Catholic officials regard genuine demonic possession as an extremely rare phenomenon that is easily confounded with natural mental disturbances. Despite that fact, every diocese is required to have at least one priest that is an exorcist, or is trained to perform exorcisms (17). As the demand for exorcisms has increased over the past few decades, the number of trained exorcists has also risen. In prior times, exorcists were kept fairly anonymous, and the performance of exorcisms remained a secret. Some exorcists attribute the rise in demand of exorcisms to the rise in drug abuse and violence, which leads to the suggestion that such things might work hand in hand. Many times a person just needs spiritual or medical help, especially if drugs or other addictions are present. The specially trained priest and medical professionals will be able to work together to address the patient, and be able to determine what type of illness the patient is suffering from. After the need of the person has been determined then the appropriate help will be met. In the circumstance of spiritual help, prayers may be offered, or the laying on of hands or a counseling session may be prescribed. The exorcist might not perform an exorcism if he does not know the person.
The Exorcist (film)
Lankester Merrin, a veteran Catholic priest who performed an exorcism in the 1950s, is on an archaeological dig in the ancient city of Hatra in Iraq. There he finds an amulet that resembles a statue of Pazuzu, a demon of ancient origins with whose history Merrin is familiar.
In Georgetown, actress Chris MacNeil is living on location with her 12-year-old daughter Regan; she is starring in a film about student activism directed by her friend and associate Burke Dennings. After playing with a Ouija board and contacting a supposedly imaginary friend whom she calls Captain Howdy, Regan begins acting strangely, including making mysterious noises, stealing, constantly using obscene language and exhibiting abnormal strength. Chris hosts a party, during which Regan comes downstairs unannounced, tells one of the guests—an astronaut—that he will die in space and then urinates on the floor. Later, Regan's bed begins to shake violently, adding further to her mother's horror. Chris consults a number of physicians, but Dr. Klein and his associates find nothing physiologically wrong with her daughter, despite Regan undergoing a battery of diagnostic tests. 
One night when Chris is out, Burke Dennings is babysitting a heavily sedated Regan. Chris returns to hear he has died falling out the window. Although this is assumed to have been an accident given Burke's history of heavy drinking, his death is investigated by Lieutenant William Kinderman. Kinderman interviews Chris. He also consults psychiatrist Father Damien Karras, recently shaken after the death of his frail mother.