A mental disorder or mental illness is a psychological or behavioral pattern that occurs in an individual and is thought to cause distress or disability that is not expected as part of normal development or culture. The recognition and understanding of mental disorders has changed over time and across cultures. Definitions, assessments, and classifications of mental disorders can vary, but guideline criteria listed in the ICD, DSM and other manuals are widely accepted by mental health professionals. Categories of diagnoses in these schemes may include dissociative disorders, mood disorders, anxiety disorders, psychotic disorders, eating disorders, developmental disorders, personality disorders, ambulatory disorders and many other categories. In many cases there is no single accepted or consistent cause of mental disorders, although they are often explained in terms of a diathesis-stress model and biopsychosocial model. Mental disorders have been found to be common, with over a third of people in most countries reporting sufficient criteria at some point in their life. Services for mental disorders may be based in hospitals or in the community. Mental health professionals diagnose individuals using different methodologies, often relying on case history and interview. Psychotherapy and psychiatric medication are two major treatment options, as well as supportive interventions and self-help. Treatment may be involuntary where legislation allows. Several movements campaign for changes to services and attitudes.


The definition and classification of mental disorders is a key issue for mental health and for users and providers of mental health services. Most international clinical documents use the term "mental disorder" rather than "mental illness". There is no single definition and the inclusion criteria are said to vary depending on the social, legal and political context. In general, however, a mental disorder has been characterized as a clinically significant behavioral or psychological pattern that occurs in an individual and is usually associated with distress, disability or increased risk of suffering. The term "serious mental illness" [SMI] is sometimes used to refer to more severe and long-lasting disorders. A broad definition of the term would cover mental disorder, mental retardation, personality disorder and substance dependence. The phrase "mental health problems" may be used to refer only to milder or more transient issues. There is often a criterion that a condition does not occur as part of a person's usual culture or religion. Nevertheless, the use of the term "mental" does not necessarily imply a distinction between mental dysfunction and brain dysfunction.

There are currently two widely established systems that classify mental disorders - Chapter V of the International Classification of Diseases (ICD-10), produced by the World Health Organization (WHO), and the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) produced by the American Psychiatric Association (APA). Both list categories of disorder and provide standardized criteria for diagnosis. They have deliberately converged their codes in recent revisions so that the manuals are often broadly comparable, although significant differences remain. Other classification schemes are used in non-western cultures (see, for example, the Chinese Classification of Mental Disorders. Other manuals may be used by those of alternative theoretical persuasions, for example the Psychodynamic Diagnostic Manual.

Some approaches to classification do not employ distinct categories based on cut-offs separating the abnormal from the normal. They are variously referred to as spectrum, continuum or dimensional systems. There is a significant scientific debate about the relative merits of a categorical vs a non-categorical system. There is also significant controversy about the role of science and values in classification schemes, and about the professional, legal and social uses to which they are put.


There are many different categories of mental disorder, and many different facets of human behavior and personality that can become disordered.

The state of anxiety or fear can become disordered, so that it is unusually intense or generalized over a prolonged period of time. Commonly recognized categories of anxiety disorders include specific phobia, Generalized anxiety disorder, Social Anxiety Disorder, Panic Disorder, Agoraphobia, Obsessive-Compulsive Disorder, Post-traumatic stress disorder. Relatively long lasting affective states can also become disordered. Mood disorder involving unusually intense and sustained sadness, melancholia or despair is know as Clinical depression (or Major depression), and may more generally be described as Emotional dysregulation. Milder but prolonged depression can be diagnosed as dysthymia. Bipolar disorder involves abnormally "high" or pressured mood states, known as mania or hypomania, alternating with normal or depressed mood. Whether unipolar and bipolar mood phenomena represent distinct categories of disorder, or whether they usually mix and merge together along a dimension or spectrum of mood, is under debate in the scientific literature.

Patterns of belief, language use and perception can become disordered. Psychotic disorders centrally involving this domain include Schizophrenia, and Delusional disorder. Schizoaffective disorder is a category used for individuals showing aspects of both schizophrenia and affective disorders. Schizotypy is a category used for individuals showing some of the traits associated with schizophrenia but without meeting cut-off criteria.

The fundamental characteristics of a person that influence his or her cognitions, motivations, and behaviors across situations and time - can be seen as disordered due to being abnormally rigid and maladaptive. Categorical schemes list a number of different personality disorders, such as those classed as eccentric (e.g. Paranoid personality disorder, Schizoid personality disorder, Schizotypal personality disorder), those described as dramatic or emotional (Antisocial personality disorder, Borderline personality disorder, Histrionic personality disorder, Narcissistic personality disorder) or those seen as fear-related (Avoidant personality disorder, Dependent personality disorder, Obsessive-compulsive personality disorder).

There is an emerging consensus that personality disorders, like personality traits in the normal range, incorporate a mixture of more acute dysfunctional behaviors that resolve in relatively short periods, and maladaptive temperamental traits that are relatively more stable Non-categorical schemes may rate individuals via a profile across different dimensions of personality that are not seen as cut off from normal personality variation, commonly through schemes based on the Big Five personality traits.

Other disorders may involve other attributes of human functioning. Eating practices can be disordered, at least in relatively rich industrialized areas, with either compulsive over-eating or under-eating or binging. Categories of disorder in this area include Anorexia nervosa, Bulimia nervosa, Exercise bulimia or Binge eating disorder. Sleep disorders such as Insomnia also exist and can disrupt normal sleep patterns. Sexual and gender identity disorders, such as Dyspareunia or Gender identity disorder or ego-dystonic homosexuality. People who are abnormally unable to resist urges, or impulses, to perform acts that could be harmful to themselves or others, may be classed as having an impulse control disorder, including various kinds of Tic disorders such as Tourette's Syndrome, and disorders such as Kleptomania (stealing) or Pyromania (fire-setting). Substance-use disorders include Substance abuse disorder. Addictive gambling may be classed as a disorder. Inability to sufficiently adjust to life circumstances may be classed as an Adjustment disorder. The category of adjustment disorder is usually reserved for problems beginning within three months of the event or situation and ending within six months after the stressor stops or is eliminated. People who suffer severe disturbances of their self-identity, memory and general awareness of themselves and their surroundings may be classed as having a Dissociative identity disorder, such as Depersonalization disorder or Dissociative Identity Disorder itself (which has also been called multiple personality disorder, or "split personality"). Factitious disorders, such as Munchausen syndrome, also exist where symptoms are experienced and/or reported for personal gain.

Disorders appearing to originate in the body, but thought to be mental, are known as somatoform disorders, including Somatization disorder. There are also disorders of the perception of the body, including Body dysmorphic disorder. Neurasthenia is a category involving somatic complaints as well as fatigue and low spirits/depression, which is officially recognized by the ICD-10 but not by the DSM-IV. Memory or cognitive disorders, such as amnesia or Alzheimer's disease exist.


Different societies or cultures and even different individuals in a culture can disagree as to what constitutes optimal vs. pathological biological and psychological functioning.Research has demonstrated that cultures vary in the relative importance placed on, for example, happiness, autonomy, or social relationships for pleasure. Likewise, the fact that a behaviour pattern is valued, accepted, encouraged, or even statistically normative in a culture does not necessarily mean that it is conducive to optimal psychological functioning.

People in all cultures find some behaviours bizarre or even incomprehensible. But just what they feel is bizarre or incomprehensible is ambiguous and subjective These differences in determination can become highly contentious.

Intangible experiences

Religious, spiritual, or transpersonal experiences and beliefs are typically not defined as disordered, especially if widely shared, despite meeting many criteria of delusional or psychotic disorders. Even when a belief or experience can be shown to produce distress or disability, the ordinary standard for judging mental disorders; the presence of a strong cultural basis for that belief, experience, or interpretation of experience generally disqualifies it from counting as evidence of mental disorder.

Psychosocial variables

In the mental health community, the psychosocial interaction is being discussed.

In recent years, some psychiatrists and psychologists have argued that current diagnostic standards tend to overstate or misinterpret neurophysiological findings and to understate the scientific importance of social-psychological variables.Advocating a more culturally sensitive approach to psychology, critics such as Carl Bell and Marcello Maviglia contend that the cultural and ethnic diversity of individuals is often discounted by researchers and service

Western bias

Current diagnostic guidelines have been criticized as having a fundamentally Euro-American outlook. They have been widely implemented, but opponents argue that even when diagnostic criteria are accepted across different cultures, it does not mean that the underlying constructs have any validity within those cultures; even reliable application can prove only consistency, not legitimacy.

Cross-cultural psychiatrist Arthur Kleinman contends that the Western bias is ironically illustrated in the introduction of cultural factors to the DSM-IV: that disorders or concepts from non-Western or non-mainstream cultures are described as "culture-bound", whereas standard psychiatric diagnoses are given no cultural qualification whatsoever, reveals to Kleinman an underlying assumption that Western cultural phenomena are universal. Kleinman's negative view towards the culture-bound syndrome is largely shared by other cross-cultural critics, common responses included both disappointment over the large number of documented non-Western mental disorders still left out and frustration that even those included were often misinterpreted or misrepresented

Many mainstream psychiatrists are dissatisfied with the new culture-bound diagnoses, although for different reasons. Robert Spitzer, a lead architect of the DSM-III, has opined that adding cultural formulations was an attempt to placate cultural critics and that the formulations lack any scientific motivation or support. Spitzer also posits that the new culture-bound diagnoses are rarely used, maintaining that the standard diagnoses apply regardless of the culture involved. In general, mainstream psychiatric opinion remains that if a diagnostic category is valid, cross-cultural factors are either irrelevant or are significant only to specific symptom presentations.


Clinical conceptions of mental illness also overlap with cultural values and in the realm of morality and social behaviour, so much so that it is sometimes argued that separating the two would be impossible without fundamentally redefining a person's role in societyIn clinical psychiatry, persistent distress and disability indicate an internal disorder requiring treatment; but in another context, that same distress and disability can be seen as an indicator of emotional struggle and the need to address social and structural problems. This dichotomy has lead some academics and clinicians to advocate a postmodernist conceptualization of mental distress and well-being.

Such approaches, along with cross-cultural and "heretical" psychologies centred on alternative cultural and ethnic identities and experiences, stand in contrast to the mainstream psychiatric community's active avoidance of any involvement with either morality or culture.[21]


Many mental health professionals, particularly psychiatrists, seek to diagnose individuals by ascertaining their particular mental disorder. Some professionals, for example some clinical psychologists, may avoid diagnosis in favor of other assessment methods such as formulation of a client's difficulties and circumstances. The majority of mental health problems are actually assessed and treated by family physicians during consultations, who may refer on for more specialist diagnosis in acute or chronic cases. Routine diagnostic practice in mental health services typically involves an interview (which may be referred to as a mental status examination), where judgments are made of the interviewee's appearance and behavior, self-reported symptoms, mental health history, and current life circumstances. The views of relatives or other third parties may be taken into account. A physical examination to check for ill health or the effects of medications or other drugs may be conducted. Psychological testing is sometimes used via paper-and-pen or computerized questionnaires, which may include algorithms based on ticking off standardized diagnostic criteria, and in relatively rare specialist cases neuroimaging tests may be requested, but these methods are more commonly found in research studies than routine clinical practice. Time and budgetary constraints often limit practicing psychiatrists from conducting more thorough diagnostic evaluations.It has been found that most clinicians evaluate patients using an unstructured, open-ended approach, with limited training in evidence-based assessment methods, and that inaccurate diagnosis may be common in routine practice.Mental illness involving hallucinations or delusions (especially schizophrenia) are prone to misdiagnosis in developing countries due to the presence of psychotic symptoms instigated by nutritional deficiencies. Comorbidity is very common in psychiatric diagnosis, i.e. the same person given a diagnosis in more than one category of disorder.

Services and treatments

Treatment and support may be provided in psychiatric hospitals, clinics or any of a diverse range of community mental health services. Often an individual may engage in different treatment modalities. A strong sense of being part of an interdependent society in developing countries makes the community-based treatment model the most effective mode of treatment. A combination of community-based treatment and the use of typical antipsychotic drugs have been found to yield the most positive, cost-effective results. Individuals may be treated against their will in some cases. Services in many countries are increasingly based on a Recovery model that supports an individual's personal journey to regain a meaningful life.


A major option for many mental disorders is psychotherapy. There are several main types. Cognitive behavioral therapy (CBT) is widely used and is based on modifying the patterns of thought and behavior associated with a particular disorder. Psychoanalysis, addressing underlying psychic conflicts and defenses, has been a dominant school of psychotherapy and is still in use. Systemic therapy or family therapy is sometimes used, addressing a network of significant others as well as an individual. Some psychotherapies are based on a humanistic approach. There are a number of specific therapies used for particular disorders, which may be offshoots or hybrids of the above types. Mental health professionals often employ an eclectic or integrative approach. Much may depend on the therapeutic relationship, and there may be problems with trust, confidentiality and engagement.


A major option for many mental disorders is psychiatric medication. There are several main groups.

Antidepressants are used for the treatment of clinical depression as well as often for anxiety and other disorders. There are a number of antidepressants beginning with the tricyclics, moving through a wide variety of drugs that modify various facets of the brain chemistry dealing with intercellular communication. Beta-blockers, developed as a heart medication, are also used as an antidepressant.

Anxiolytics are used for anxiety disorders and related problems such as insomnia.

Mood stabilizers are used primarily in bipolar disorder. Lithium carbonate (a salt) and Lamictal (an epileptic drug) are notable for treating both mania and depression. The others, mainly targeting mania rather than depression, are a wide variety of epilepsy medications and antipsychotics.

Antipsychotics are used for psychotic disorders, notably for positive symptoms in schizophrenia. Although there has not been any evidence of the superiority of newer, atypical antipsychotic drugs, they are being prescribed to individuals throughout the world. The prescription of relatively cheaper, older typical antipsychotic drugs is also used.

Stimulants are commonly used, notably for ADHD. Despite the different conventional names of the drug groups, there can be considerable overlap in the kinds of disorders for which they are actually indicated.

There may also be off-label use of medications. There can be problems with adverse effects of medication and adherence.

Recently, the pharmaceutical industry has come into severe criticism for hiding negative results from clinical trials from the public and the USFDA and for promoting medications for unapproved uses by pharmaceutical sales representatives. Prominent psychiatric researchers have also come under fire recently for failing to disclose drug company compensation which poses serious potential conflicts of interest with their research and professional activities.


Electroconvulsive therapy (ECT) is sometimes used in severe cases when other interventions for severe intractable depression have failed. Psychosurgery is considered experimental but is advocated by certain neurologists in certain rare cases.[27][28]

Psychoeducation may be used to provide people with the information to understand and manage their problems. Creative therapies are sometimes used, including music therapy, art therapy or drama therapy. Lifestyle adjustments and supportive measures are often used, including peer support, self-help groups for mental health and supported housing or supported employment (including social firms). Some advocate dietary supplements. Many things have been found to help at least some people. A placebo effect may play a role in any intervention.


Prognosis depends on the disorder, the individual and numerous related factors. Some disorders are transient, while others may last a lifetime. Some disorders may be very limited in their functional effects, while others may involve substantial disability and support needs. The degree of ability or disability may vary across different life domains. Continued disability has been linked to institutionalization, discrimination and social exclusion as well as to the inherent properties of disorders.

Even those disorders often considered the most serious and intractable have varied courses. Long-term international studies of schizophrenia have found that over a half of individuals recover in terms of symptoms, and around a fifth to a third in terms of symptoms and functioning, with some requiring no medication. At the same time, many have serious difficulties and support needs for many years, although "late" recovery is still possible. The World Health Organization concluded that the long-term studies' findings converged with others in "relieving patients, carers and clinicians of the chronicity paradigm which dominated thinking throughout much of the 20th century."Around half of people initially diagnosed with bipolar disorder achieve syndromal recovery (no longer meeting criteria for the diagnosis) within six weeks, and nearly all achieve it within two years, with nearly half regaining their prior occupational and residential status in that period. However, nearly half go on to experience a new episode of mania or major depression within the next two years. Functioning has been found to vary, being poor during periods of major depression or mania but otherwise fair to good, and possibly superior during periods of hypomania in Bipolar II.

Despite often being characterized in purely negative terms, some mental states labeled as disorders can also involve above-average creativity, non-conformity, goal-striving, meticulousness, or empathy. In addition, the public perception of the level of disability associated with mental disorders can change.


Mental disorders have been found to be relatively common, with more than one in three people in most countries reporting sufficient criteria for at least one diagnosis at some point in their life up to the time they were assessed. A new WHO global survey currently underway indicates that anxiety disorders are the most common in all but 1 country, followed by mood disorders in all but 2 countries, while substance disorders and impulse-control disorders were consistently less prevalent. Rates varied by region. Such statistics are widely believed to be underestimates, due to poor diagnosis (especially in countries without affordable access to mental health services) and low reporting rates, in part because of the predominant use of self-report data rather than semi-structured instruments. Actual lifetime prevalence rates for mental disorders are estimated to be between 65% and 85%.

A review of anxiety disorder surveys in different countries found average lifetime prevalence estimates of 16.6%, with women having higher rates on average.A review of mood disorder surveys in different countries found lifetime rates of 6.7% for major depressive disorder (higher in some studies, and in women) and 0.8% for bipolar 1 disorder.

The updated US National Comorbidity Survey (NCS) reported that nearly half of Americans (46.4%) meet criteria at some point in their life for either an anxiety disorder (28.8%), mood disorder (20.8%), impulse-control disorder (24.8%) or substance use disorder (14.6%).

A 2004 cross-Europe study found that approximately one in four people reported meeting criteria at some point in their life for at least one of the DSM-IV disorders assessed, which included mood disorders (13.9%), anxiety disorders (13.6%) or alcohol disorder (5.2%). Approximately one in ten met criteria within a 12-month period. Women and younger people of either gender showed more cases of disorder. A 2005 review of surveys in 16 European countries found that 27% of adult Europeans are affected by at least one mental disorder in a 12 month period

An international review of studies on the prevalence of schizophrenia found an average (median) figure of 0.4% for lifetime prevalence; it was consistently lower in poorer countries.

Studies of the prevalence of personality disorders (PDs) have been fewer and smaller-scale, but one broad Norwegian survey found a five-year prevalence of almost 1 in 7 (13.4%). Rates for specific disorders ranged from 0.8% to 2.8%, differing across countries, and by gender, educational level and other factors. A US survey that incidentally screened for personality disorder found a rate of 14.79%.

Approximately 7% of a preschool pediatric sample were given a psychiatric diagnosis in one clinical study, and approximately 10% of 1- and 2-year-olds receiving developmental screening have been assessed as having significant emotional/behavioral problems based on parent and pediatrician reports.


Eight women representing prominent mental diagnoses in the nineteenth century. (Armand Gautier)

Ancient civilizations

Ancient civilisations described and treated a number of mental disorders. The Greeks coined terms for melancholy, hysteria and phobia and developed the humorism theory. Psychiatric theories and treatments developed in Persia, Arabia and the Muslim Empire, particularly in the medieval Islamic world from the 8th century, where the first psychiatric hospitals were built.


Middle Ages

Conceptions of madness in the Middle Ages in Christian Europe were a mixture of the divine, diabolical, magical and humoral, as well as more down to earth considerations. In the early modern period, some people with mental disorders may have been victims of the witch-hunts but were increasingly admitted to local workhouses and jails or sometimes to private madhouses. Many terms for mental disorder that found their way into everyday use first became popular the 16th and 17th centuries.

ighteenth century

By the end of the 17th century and into the Enlightenment, madness was increasingly seen as an organic physical phenomenon with no connection to the soul or moral responsibility. Asylum care was often harsh and treated people like wild animals, but towards the end of the 18th century a moral treatment movement gradually developed. Clear descriptions of some syndromes may be relatively rare prior to the 1800s.

Nineteenth century

Industrialization and population growth led to a massive expansion of the number and size of insane asylums in every Western country in the 19th century. Numerous different classification schemes and diagnostic terms were developed by different authorities, and the term psychiatry was coined, though medical superintendents were still known as alienists.

Twentieth century

The turn of the 20th century saw the development of psychoanalysis, which would later come to the fore, along with Kraepelin's classification scheme. Asylum "inmates" were increasingly referred to as "patients" and asylums renamed as hospitals.

Europe and the U.S.

In the twentieth century in the United States, a mental hygiene movement developed, aiming to prevent mental disorders. Clinical psychology and social work developed as professions. World War I saw a massive increase of conditions that came to be termed "shell shock."

World War II saw the development in the U.S. of a new psychiatric manual for categorizing mental disorders, which along with existing systems for collecting census and hospital statistics led to the first Diagnostic and Statistical Manual of Mental Disorders (DSM). The International Classification of Diseases (ICD) followed suit with a section on mental disorders.

The term stress, having emerged out of endocrinology work in the 1930s, was increasingly applied to mental disorders. Electroconvulsive therapy, insulin shock therapy, lobotomies and the "neuroleptic" chlorpromazine came to be used by mid-century. An antipsychiatry movement came to the fore in the 1960s. Deinstitutionalization gradually occurred in the West, with isolated psychiatric hospitals being closed down in favor of community mental health services. A consumer/survivor movement gained momentum. Other kinds of psychiatric medication gradually came into use, such as "psychic energizers" and lithium. Benzodiazepines gained widespread use in the 1970s for anxiety and depression, until dependency problems curtailed their popularity.

Advances in neuroscience and genetics led to new research agendas. Cognitive behavioral therapy was developed. The DSM and then ICD adopted new criteria-based classifications, and the number of "official" diagnoses saw a large expansion. Through the 1990s, new SSRI antidepressants became some of the most widely prescribed drugs in the world. Also during the 1990s, a recovery model developed.

Professions and fields

A number of professions have developed that specialise in the treatment of mental disorders, including the medical speciality of psychiatry (including psychiatric nursing),a subset of psychology known as clinical psychology, social work, as well as hental health counselors, marriage and family therapists, psychotherapists, counselors and public health professionals. Those with personal experience of using mental health services are also increasingly involved in researching and delivering mental health services and working as mental health professionals.The different clinical and scientific perspectives draw on diverse fields of research and theory, and different disciplines may favor differing models, explanations and goals.


The consumer/survivor movement (also known as user/survivor movement) is made up of individuals (and organizations representing them) who are clients of mental health services or who consider themselves "survivors" of mental health services. The movement campaigns for improved mental health services and for more involvement and empowerment within mental health services, policies and wider society. Patient advocacy organizations have expanded with increasing deinstitutionalization in developed countries, working to challenge the stereotypes, stigma and exclusion associated with psychiatric co