The classification of mental disorders, also known as psychiatric nosology or psychiatric taxonomy, is central to the practice of psychiatry and other mental health professions. The two most widely used psychiatric classification systems are the International Classification of Diseases, 11th edition (ICD-11; in effect since 1 January 2022.), produced by the World Health Organization (WHO); and the Diagnostic and Statistical Manual of Mental Disorders produced by the American Psychiatric Association since 1952. The latest edition is the Fifth Edition, Text Revision (DSM-5-TR), which was released in 2022. The ICD is a broad medical classification system; mental disorders are contained in Chapter 06: Mental, behavioural or neurodevelopmental disorders (06). Both systems list disorders thought to be distinct types, and in recent revisions the two systems have deliberately converged their codes so that their manuals are often broadly comparable, though differences remain. Both classifications employ operational definitions. Other classification schemes, used more locally, include the Chinese Classification of Mental Disorders. Manuals of limited use, by practitioners with alternative theoretical persuasions, include the Psychodynamic Diagnostic Manual.
Definitions In the scientific and academic literature on the definition or categorization of mental disorders, one extreme argues that it is entirely a matter of value judgments (including of what is normal) while another proposes that it is or could be entirely objective and scientific (including by reference to statistical norms); other views argue that the concept refers to a "fuzzy prototype" that can never be precisely defined, or that the definition will always involve a mixture of scientific facts (e.g. that a natural or evolved function is not working properly) and value judgments (e.g. that it is harmful or undesired). Lay concepts of mental disorder vary considerably across different cultures and countries, and may refer to different sorts of individual and social problems. The WHO and national surveys report that there is no single consensus on the definition of mental disorder, and that the phrasing used depends on the social, cultural, economic and legal context in different contexts and in different societies. The WHO reports that there is intense debate about which conditions should be included under the concept of mental disorder; a broad definition can cover mental illness, intellectual disability, personality disorder and substance dependence, but inclusion varies by country and is reported to be a complex and debated issue. There may be a criterion that a condition should not be expected to occur as part of a person's usual culture or religion. However, despite the term "mental", there is not necessarily a clear distinction drawn between mental (dys)functioning and brain (dys)functioning, or indeed between the brain and the rest of the body. Most international clinical documents avoid the term "mental illness", preferring the term "mental disorder". However, some use "mental illness" as the main overarching term to encompass mental disorders. Some consumer/survivor movement organizations oppose use of the term "mental illness" on the grounds that it supports the dominance of a medical model. The term "serious mental impairment" (SMI) is sometimes used to refer to more severe and long-lasting disorders while "mental health problems" may be used as a broader term, or to refer only to milder or more transient issues. Confusion often surrounds the ways and contexts in which these terms are used. Mental disorders are generally classified separately to neurological disorders, learning disabilities or intellectual disabilities.
Classification systems
ICD-10
The International Classification of Diseases (ICD) is an international standard diagnostic classification for a wide variety of health conditions. The ICD-10 states that mental disorder is "not an exact term", although it is generally used "...to imply the existence of a clinically recognisable set of symptoms or behaviours associated in most cases with distress and with interference with personal functions." Chapter V focuses on "mental and behavioural disorders" and consists of 10 main groups:
F0 – F9: Organic, including symptomatic mental disorders F10 – F-19: Mental and behavioural disorders due to use of psychoactive substances F20 – F29: Schizophrenia, schizotypal and delusional disorders F30 – F39: Mood (affective) disorders F40 – F49: Neurotic, stress-related and somatoform disorders F50 – F59: Behavioural syndromes associated with physiological disturbances and physical factors F60 – F69: Disorders of personality and behaviour in adult persons F70 – F79: Mental retardation F80 – F89: Disorders of psychological development F90 – 98: Behavioural and emotional disorders with onset usually occurring in childhood and adolescence In addition, a group of F99 "unspecified mental disorders". Within each group, there are more specific subcategories.
ICD-11
The WHO has revised ICD-10 to produce the latest version, ICD-11, adopted by the 72nd World Health Assembly in 2019, and came into effect on 1 January 2022. The ICD is a broad medical classification system; mental disorders are contained in Chapter 06: Mental, behavioural or neurodevelopmental disorders (06).
DSM-IV
The DSM-IV was originally published in 1994 and listed more than 250 mental disorders. It was produced by the American Psychiatric Association and it characterizes mental disorder as "a clinically significant behavioral or psychological syndrome or pattern that occurs in an individual,...is associated with present distress...or disability...or with a significantly increased risk of suffering" but that "...no definition adequately specifies precise boundaries for the concept of 'mental disorder'...different situations call for different definitions" (APA, 1994 and 2000). The DSM also states that "there is no assumption that each category of mental disorder is a completely discrete entity with absolute boundaries dividing it from other mental disorders or no mental disorders." The DSM-IV-TR (Text Revision, 2000) consisted of five axes (domains) on which disorders could be assessed. The five axes were:
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