the prefix para-, the term crops up causing trouble as the contentious but stubbornly persistent concept of paraphrenia". At least 50% of the diagnosed cases of schizophrenia experience delusions of reference and delusions of persecution. Paranoia perceptions and behavior may be part of many mental illnesses, such as depression and dementia, but they are more prevalent in three mental disorders: paranoid schizophrenia, delusional disorder (persecutory type), and paranoid personality disorder. Treatment Paranoid delusions are often treated with antipsychotic medication, which exert a medium effect size. Cognitive behavioral therapy (CBT) improves paranoid delusions relative to control conditions according to a meta-analysis. A meta-analysis of 43 studies reported that metacognitive training (MCT) reduces (paranoid) delusions at a medium to large effect size relative to control conditions. History The word paranoia comes from the Greek παράνοια (paránoia), "madness", and that from παρά (pará), "beside, by" and νόος (nóos), "mind". The term was used to describe a mental illness in which a delusional belief is the sole or most prominent feature. In this definition, the belief does not have to be persecutory to be classified as paranoid, so any number of delusional beliefs can be classified as paranoia. For example, a person who has the sole delusional belief that they are an important religious figure would be classified by Kraepelin as having 'pure paranoia'. The word “paranoia” is associated from the Greek word “para-noeo”. Its meaning was "derangement", or "departure from the normal". However, the word was used strictly and other words were used such as "insanity" or "crazy", as these words were introduced by Aurelius Cornelius Celsus. The term “paranoia” first made an appearance during plays of Greek tragedians, and was also used by sufficient individuals such as Plato and Hippocrates. Nevertheless, the word “paranoia” was the equivalent of “delirium” or “high fever”. Eventually, the term made its way out of everyday language for two millennia. “Paranoia” was soon revived as it made an appearance in the writings of the nosologists. It began to take appearance in France, with the writings of Rudolph August Vogel (1772) and François Boissier de Sauvage (1759). According to Michael Phelan, Padraig Wright, and Julian Stern (2000), paranoia and paraphrenia are debated entities that were detached from dementia praecox by Kraepelin, who explained paranoia as a continuous systematized delusion arising much later in life with no presence of either hallucinations or a deteriorating course, paraphrenia as an identical