A mental disorder, also referred to as a mental illness, a mental health condition, or a psychiatric disability, is a behavioral or mental pattern that causes significant distress or impairment of personal functioning. A mental disorder is also characterized by a clinically significant disturbance in an individual's cognition, emotional regulation, or behavior, often in a social context. Such disturbances may occur as single episodes, may be persistent, or may be relapsing–remitting. There are many different types of mental disorders, with signs and symptoms that vary widely between specific disorders. A mental disorder is one aspect of mental health.

The causes of mental disorders are often unclear. Theories incorporate findings from a range of fields. Disorders may be associated with particular regions or functions of the brain. Disorders are usually diagnosed or assessed by a mental health professional, such as a clinical psychologist, psychiatrist, psychiatric nurse, or clinical social worker, using various methods such as psychometric tests, but often relying on observation and questioning. Cultural and religious beliefs, as well as social norms, should be taken into account when making a diagnosis.

Services for mental disorders are usually based in psychiatric hospitals, outpatient clinics, or in the community. Treatments are provided by mental health professionals. Common treatment options are psychotherapy or psychiatric medication, while lifestyle changes, social interventions, peer support, and self-help are also options. In a minority of cases, there may be involuntary detention or treatment. Prevention programs have been shown to reduce depression.

In 2019, common mental disorders around the globe include: major depression, which affects about 264 million people; dementia, which affects about 50 million; bipolar disorder, which affects about 45 million; and schizophrenia and other psychoses, which affect about 20 million people. Neurodevelopmental disorders include attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (autism), and intellectual disability, of which onset occurs early in the developmental period. Stigma and discrimination can add to the suffering and disability associated with mental disorders, leading to various social movements attempting to increase understanding and challenge social exclusion.

Definition The definition and classification of mental disorders are key issues for researchers as well as service providers and those who may be diagnosed. For a mental state to be classified as a disorder, it generally needs to cause dysfunction. Most international clinical documents use the term mental "disorder", while "illness" is also common. It has been noted that using the term "mental" (i.e., of the mind) is not necessarily meant to imply separateness from the brain or body, although the distinction between mind and brain, as well as the question of their fundamental nature, is often insufficiently examined in psychiatry.

According to the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), published in 1994, a mental disorder is a psychological syndrome or pattern that is associated with distress (e.g., via a painful symptom), disability (impairment in one or more important areas of functioning), increased risk of death, or causes a significant loss of autonomy; however, it excludes normal responses such as the grief from loss of a loved one and also excludes deviant behavior for political, religious, or societal reasons not arising from a dysfunction in the individual.

The DSM-IV definition states that, like many medical terms, mental disorder "lacks a consistent operational definition that covers all situations". It notes that different levels of abstraction can be used for medical definitions, including pathology, symptomology, deviance from a normal range, or etiology, and that the same is true for mental disorders, so that sometimes one type of definition is appropriate and sometimes another, depending on the situation.

In 2013, the American Psychiatric Association (APA) redefined mental disorders in the DSM-5 as "a syndrome characterized by clinically significant disturbance in an individual's cognition, emotion regulation, or behavior that reflects a dysfunction in the psychological, biological, or developmental processes underlying mental functioning." The final draft of ICD-11 contains a very similar definition.

Nervous illness

A mental breakdown, nervous breakdown or mental health crisis is an acute, time-limited, mental disorder that manifests primarily as severe, stress-induced depression, anxiety, paranoia, or dissociation in a previously functional individual, to the extent that they are no longer able to function on a day-to-day basis until the disorder is resolved. A nervous breakdown is often closely tied to psychological burnout, severe overwork, sleep deprivation, and similar stressors, which may combine to temporarily overwhelm an individual with otherwise sound mental functions. A mental breakdown can last for hours at a time, to months at a time. While these time periods can vary between different people, their reactions to the mental breakdown may also vary. These terms have not been formally defined through a medical diagnostic system such as the DSM-5 or ICD-10 and are nearly absent from scientific literature regarding mental illness.Hall-Flavin, Daniel K. (26 October 2016). "Nervous Breakdown" Mayo Clinic. Archived copy, 2 November 2021. In addition to the concept of mental disorder, some people have argued for a return to the old-fashioned concept of nervous illness. In How Everyone Became Depressed: The Rise and Fall of the Nervous Breakdown (2013), Edward Shorter, a professor of psychiatry and the history of medicine, says:

Classifications

There are currently two widely established systems that classify mental disorders: International Classification of Diseases produced by the WHO. The latest edition is the ICD-11, which is in effect since 1 January 2022. The ICD is a broad medical classification system; mental disorders are contained in Chapter 06: Mental, behavioural or neurodevelopmental disorders (). 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.

Both of these 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 may be used in non-western cultures, for example, the Chinese Classification of Mental Disorders, and other manuals may be used by those of alternative theoretical persuasions, such as the Psychodynamic Diagnostic Manual. In general, mental disorders are classified separately from neurological disorders, learning disabilities or intellectual disability. Additionally, there are separate diagnostic schemes for mental illness in intellectual disability, such as the American Diagnostic Manual - Intellectual Disability and the British DC-LD.

Unlike the DSM and ICD, some approaches are not based on identifying distinct categories of disorder using dichotomous symptom profiles intended to separate the abnormal from the normal. There is significant scientific debate about the relative merits of categorical versus such non-categorical (or hybrid) schemes, also known as continuum or dimensional models. A spectrum approach may incorporate elements of both.

In the scientific and academic literature on the definition or classification of mental disorder, one extreme argues that it is entirely a matter of value judgements (including of what is normal) while another proposes that it is or could be entirely objective and scientific (including by reference to statistical norms). Common hybrid views argue that the concept of mental disorder is objective even if only a "fuzzy prototype" that can never be precisely defined, or conversely that the concept always involves a mixture of scientific facts and subjective value judgments.Perring, C. (2005) Mental Illness Stanford Encyclopedia of Philosophy Although the diagnostic categories are referred to as 'disorders', they are presented as medical diseases, but are not validated in the same way as most medical diagnoses. Some neurologists argue that classification will only be reliable and valid when based on neurobiological features rather than clinical interview, while others suggest that the differing ideological and practical perspectives need to be better integrated.

The DSM and ICD approach remains under attack both because of the implied causality model and because some researchers believe it better to aim at underlying brain differences which can precede symptoms by many years.

Dimensional models The high degree of comorbidity between disorders in categorical models such as the DSM and ICD have led some to propose dimensional models. Studying comorbidity between disorders have demonstrated two latent (unobserved) factors or dimensions in the structure of mental disorders that are thought to possibly reflect etiological processes. These two dimensions reflect a distinction between internalizing disorders, such as mood or anxiety symptoms, and externalizing disorders such as behavioral or substance use symptoms. A single general factor of psychopathology, similar to the g factor for intelligence, has been empirically supported. The p factor model supports the internalizing-externalizing distinction, but also supports the formation of a third dimension of thought disorders such as schizophrenia. Biological evidence also supports the validity of the internalizing-externalizing structure of mental disorders, with twin and adoption studies supporting heritable factors for externalizing and internalizing disorders. A leading dimensional model is the Hierarchical Taxonomy of Psychopathology.

Disorders

There are many different categories of mental disorder, and many different facets of human behavior and personality that can become disordered.Gazzaniga, M.S., & Heatherton, T.F. (2006). Psychological Science. New York: W.W. Norton & Company, Inc.Teacher's Guide: Information about Mental Illness and the Brain National Institute of Mental Health. 2005. Curriculum supplement from The NIH Curriculum Supplements Series

Anxiety disorders

An anxiety disorder is anxiety or fear that interferes with normal functioning. Commonly recognized categories include specific phobias, generalized anxiety disorder, social anxiety disorder, panic disorder, agoraphobia, and post-traumatic stress disorder. Obsessive–compulsive disorder was categorized as an anxiety disorder in DSM-III, which was published in 1980, but was later placed in its own section called "Obsessive-Compulsive and Related Disorder" in DSM-5.

Mood disorders

Other affective (emotion/mood) processes can also become disordered. Mood disorder involving unusually intense and sustained sadness, melancholia, or despair is known as major depression (also known as unipolar or clinical depression). Milder, but still prolonged depression, can be diagnosed as dysthymia. Bipolar disorder (also known as manic depression) involves abnormally "high" or pressured mood states, known as mania or hypomania, alternating with normal or depressed moods. The extent to which unipolar and bipolar mood phenomena represent distinct categories of disorder, or mix and merge along a dimension or spectrum of mood, is subject to some scientific debate.

Psychotic disorders