Anumber of randomized controlled trials showed the efficacy ofcognitive-behavioral therapy (CBT) in patients with psychotic disorders whenthe therapy was added to the antipsychotic medication. Given the strong evidencesupporting the efficacy of CBT for psychosis, CBT was included in the NICEguidelines. Up to the eighties of the 20th century, the attempts to influencedelusional beliefs by psychotherapy seemed to be unnecessary, sometimes evendangerous, and there were apprehensions that the patient might lose trust inthe psychiatrist. The first systematic attempts to influence delusional beliefsthrough psychotherapy appeared at the end of the eighties. The experience gainedfrom studies from this time showed that the content of delusions could beunderstood from personal experience and psychotherapy could be effective atleast in some patients.

Thepatient with chronic delusions gradually learns through inductive questioningto distinguish between perception and interpretation, firstly on the peripheryof the vicious system. Then he learns the Socratic dialogue himself tochallenge false assumptions, provide an alternative hypothesis, and test thebeliefs by behavioral experiments. The therapy includes an interconnection ofdelusional system with core schemas and conditional rules that the delusionalsystem originally arises from and now is involved in its maintenance.