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A mental disorder, also called a mental illness or psychiatric disorder, is a behavioral or mental pattern that may cause suffering or a poor ability to function in life. Such features may be persistent, relapsing and remitting, or occur as a single episode. Many disorders have been described, with signs and symptoms that vary widely between specific disorders. Such disorders may be diagnosed by a mental health professional. The causes of mental disorders are often unclear. Theories may incorporate findings from a range of fields. Mental disorders are usually defined by a combination of how a person behaves, feels, perceives, or thinks. This may be associated with particular regions or functions of the brain, often in a social context. A mental disorder is one aspect of mental health. Cultural and religious beliefs, as well as social norms, should be taken into account when making a diagnosis. Services are based in psychiatric hospitals or in the community, and assessments are carried out by psychiatrists, psychologists, and clinical social workers, using various methods but often relying on observation and questioning. Treatments are provided by various mental health professionals. Psychotherapy and psychiatric medication are two major treatment options. Other treatments include social interventions, peer support, and self-help. In a minority of cases there might be involuntary detention or treatment. Prevention programs have been shown to reduce depression. Common mental disorders include depression, which affects about 400 million, dementia which affects about 35 million, and schizophrenia, which affects about 21 million people globally. 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.


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 classify 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 brain or body. According to DSM-IV, a mental disorder is a psychological syndrome or pattern which 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 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. DSM-IV precedes the definition with caveats, stating that, as in the case with many medical terms, mental disorder "lacks a consistent operational definition that covers all situations", noting 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.


There are currently two widely established systems that classify mental disorders:
ICD-10 Chapter V: Mental and behavioural disorders, since 1949 part of the International Classification of Diseases produced by the WHO, the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) produced by the American Psychiatric Association (APA) since 1952. 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, for example the Psychodynamic Diagnostic Manual. In general, mental disorders are classified separately from neurological disorders, learning disabilities or intellectual disability. 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. 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.
​Mental Disorders

There are many different categories of mental disorder, and many different facets of human behavior and personality that can become disordered. Anxiety or fear that interferes with normal functioning may be classified as an anxiety disorder. Commonly recognized categories include specific phobias, generalized anxiety disorder, social anxiety disorder, panic disorder, agoraphobia, obsessive-compulsive disorder and post-traumatic stress disorder. 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.[non-primary source needed]. Patterns of belief, language use and perception of reality can become disordered (e.g., delusions, thought disorder, hallucinations). Psychotic disorders in 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 characteristics associated with schizophrenia but without meeting cutoff criteria.
Personality—the fundamental characteristics of a person that influence thoughts and behaviors across situations and time—may be considered disordered if judged to be abnormally rigid and maladaptive. Although treated separately by some, the commonly used categorical schemes include them as mental disorders, albeit on a separate "axis II" in the case of the DSM-IV. A number of different personality disorders are listed, including those sometimes classed as "eccentric", such as paranoid, schizoid and schizotypal personality disorders; types that have described as "dramatic" or "emotional", such as antisocial, borderline, histrionic or narcissistic personality disorders; and those sometimes classed as fear-related, such as anxious-avoidant, dependent, or obsessive-compulsive personality disorders. The personality disorders, in general, are defined as emerging in childhood, or at least by adolescence or early adulthood. The ICD also has a category for enduring personality change after a catastrophic experience or psychiatric illness. If an inability to sufficiently adjust to life circumstances begins within three months of a particular event or situation, and ends within six months after the stressor stops or is eliminated, it may instead be classed as an adjustment disorder. There is an emerging consensus that so-called "personality disorders", like personality traits in general, actually incorporate a mixture of acute dysfunctional behaviors that may resolve in short periods, and maladaptive temperamental traits that are more enduring. Furthermore, there are also non-categorical schemes that rate all individuals via a profile of different dimensions of personality without a symptom-based cutoff from normal personality variation, for example through schemes based on dimensional models. Eating disorders involve disproportionate concern in matters of food and weight. Categories of disorder in this area include anorexia nervosa, bulimia nervosa, exercise bulimia or binge eating disorder. Sleep disorders such as insomnia involve disruption to normal sleep patterns, or a feeling of tiredness despite sleep appearing normal. Sexual disorders and gender dysphoria may be diagnosed, including dyspareunia and ego-dystonic homosexuality. Various kinds of paraphilia are considered mental disorders (sexual arousal to objects, situations, or individuals that are considered abnormal or harmful to the person or others). People who are abnormally unable to resist certain urges or impulses that could be harmful to themselves or others, may be classed as having an impulse control disorder, and disorders such as kleptomania (stealing) or pyromania (fire-setting). Various behavioral addictions, such as gambling addiction, may be classed as a disorder. Obsessive-compulsive disorder can sometimes involve an inability to resist certain acts but is classed separately as being primarily an anxiety disorder. The use of drugs (legal or illegal, including alcohol), when it persists despite significant problems related to its use, may be defined as a mental disorder. The DSM incorporates such conditions under the umbrella category of substance use disorders, which includes substance dependence and substance abuse. The DSM does not currently use the common term drug addiction, and the ICD simply refers to "harmful use". Disordered substance use may be due to a pattern of compulsive and repetitive use of the drug that results in tolerance to its effects and withdrawal symptoms when use is reduced or stopped. 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"). Other memory or cognitive disorders include amnesia or various kinds of old age dementia. A range of developmental disorders that initially occur in childhood may be diagnosed, for example autism spectrum disorders, oppositional defiant disorder and conduct disorder, and attention deficit hyperactivity disorder (ADHD), which may continue into adulthood. Conduct disorder, if continuing into adulthood, may be diagnosed as antisocial personality disorder (dissocial personality disorder in the ICD). Popularist labels such as psychopath (or sociopath) do not appear in the DSM or ICD but are linked by some to these diagnoses. Somatoform disorders may be diagnosed when there are problems that appear to originate in the body that are thought to be manifestations of a mental disorder. This includes somatization disorder and conversion disorder. There are also disorders of how a person perceives their body, such as body dysmorphic disorder. Neurasthenia is an old diagnosis involving somatic complaints as well as fatigue and low spirits/depression, which is officially recognized by the ICD-10 but no longer by the DSM-IV. Factitious disorders, such as Munchausen syndrome, are diagnosed where symptoms are thought to be experienced (deliberately produced) and/or reported (feigned) for personal gain. There are attempts to introduce a category of relational disorder, where the diagnosis is of a relationship rather than on any one individual in that relationship. The relationship may be between children and their parents, between couples, or others. There already exists, under the category of psychosis, a diagnosis of shared psychotic disorder where two or more individuals share a particular delusion because of their close relationship with each other.
There are a number of uncommon psychiatric syndromes, which are often named after the person who first described them, such as Capgras syndrome, De Clerambault syndrome, Othello syndrome, Ganser syndrome, Cotard delusion, and Ekbom syndrome, and additional disorders such as the Couvade syndrome and Geschwind syndrome. Various new types of mental disorder diagnosis are occasionally proposed. Among those controversially considered by the official committees of the diagnostic manuals include self-defeating personality disorder, sadistic personality disorder, passive-aggressive personality disorder and premenstrual dysphoric disorder. Two recent unique unofficial proposals are solastalgia by Glenn Albrecht and hubris syndrome by David Owen. The application of the concept of mental illness to the phenomena described by these authors has in turn been critiqued by Seamus Mac Suibhne.

Signs and symptoms


The likely course and outcome of mental disorders varies and is dependent on numerous factors related to the disorder itself, the individual as a whole, and the social environment. Some disorders are transient, while others may be more chronic in nature. Even those disorders often considered the most serious and intractable have varied courses i.e. schizophrenia, psychotic disorders, and personality disorders. 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.


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 over time and across different life domains. Furthermore, continued disability has been linked to institutionalization, discrimination and social exclusion as well as to the inherent effects of disorders. Alternatively, functioning may be affected by the stress of having to hide a condition in work or school etc., by adverse effects of medications or other substances, or by mismatches between illness-related variations and demands for regularity. It is also the case that, while often being characterized in purely negative terms, some mental traits or 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. Nevertheless, internationally, people report equal or greater disability from commonly occurring mental conditions than from commonly occurring physical conditions, particularly in their social roles and personal relationships. The proportion with access to professional help for mental disorders is far lower, however, even among those assessed as having a severely disabling condition. Disability in this context may or may not involve such things as:
Basic activities of daily living. Including looking after the self (health care, grooming, dressing, shopping, cooking etc.) or looking after accommodation (chores, DIY tasks etc.)
Interpersonal relationships. Including communication skills, ability to form relationships and sustain them, ability to leave the home or mix in crowds or particular settings
Occupational functioning. Ability to acquire a job and hold it, cognitive and social skills required for the job, dealing with workplace culture, or studying as a student.
In terms of total Disability-adjusted life years (DALYs), which is an estimate of how many years of life are lost due to premature death or to being in a state of poor health and disability, mental disorders rank amongst the most disabling conditions. Unipolar (also known as Major) depressive disorder is the third leading cause of disability worldwide, of any condition mental or physical, accounting for 65.5 million years lost. The total DALY does not necessarily indicate what is the most individually disabling because it also depends on how common a condition is; for example, schizophrenia is found to be the most individually disabling mental disorder on average but is less common. Alcohol-use disorders are also high in the overall list, responsible for 23.7 million DALYs globally, while other drug-use disorders accounted for 8.4 million. Schizophrenia causes a total loss of 16.8 million DALY, and bipolar disorder 14.4 million. Panic disorder leads to 7 million years lost, obsessive-compulsive disorder 5.1, primary insomnia 3.6, and post-traumatic stress disorder 3.5 million DALYs.
The first ever systematic description of global disability arising in youth, published in 2011, found that among 10- to 24-year-olds nearly half of all disability (current and as estimated to continue) was due to mental and neurological conditions, including substance use disorders and conditions involving self-harm. Second to this were accidental injuries (mainly traffic collisions) accounting for 12 percent of disability, followed by communicable diseases at 10 percent. The disorders associated with most disability in high income countries were unipolar major depression (20%) and alcohol use disorder (11%). In the eastern Mediterranean region it was unipolar major depression (12%) and schizophrenia (7%), and in Africa it was unipolar major depression (7%) and bipolar disorder (5%).
Suicide, which is often attributed to some underlying mental disorder, is a leading cause of death among teenagers and adults under 35. There are an estimated 10 to 20 million non-fatal attempted suicides every year worldwide.


Risk factors for mental illness include genetic inheritance, such as parents having depression, or a propensity for high neuroticism  or "emotional instability".
In depression, parenting risk factors include parental unequal treatment, and there is association with high cannabis use. In schizophrenia and psychosis, risk factors include migration and discrimination, childhood trauma, bereavement or separation in families, and abuse of drugs, including cannabis, and urbanicity.
In anxiety, risk factors may include family history (e.g. of anxiety), temperament and attitudes (e.g. pessimism), and parenting factors including parental rejection, lack of parental warmth, high hostility, harsh discipline, high maternal negative affect, anxious childrearing, modelling of dysfunctional and drug-abusing behaviour, and child abuse (emotional, physical and sexual). Environmental events surrounding pregnancy and birth have also been implicated. Traumatic brain injury may increase the risk of developing certain mental disorders. There have been some tentative inconsistent links found to certain viral infections, to substance misuse, and to general physical health. Social influences have been found to be important,[50] including abuse, neglect, bullying, social stress, traumatic events and other negative or overwhelming life experiences. For bipolar disorder, stress (such as childhood adversity) is not a specific cause, but does place genetically and biologically vulnerable individuals at risk for a more severe course of illness. The specific risks and pathways to particular disorders are less clear, however. Aspects of the wider community have also been implicated, including employment problems, socioeconomic inequality, lack of social cohesion, problems linked to migration, and features of particular societies and cultures.


Psychiatrists seek to provide a medical diagnosis of individuals by an assessment of symptoms, signs and impairment associated with particular types of mental disorder. Other mental health professionals, such as clinical psychologists, may or may not apply the same diagnostic categories to their clinical formulation of a client's difficulties and circumstances. The majority of mental health problems are, at least initially, assessed and treated by family physicians (in the UK general practitioners) during consultations, who may refer a patient on for more specialist diagnosis in acute or chronic cases. Routine diagnostic practice in mental health services typically involves an interview known as a mental status examination, where evaluations are made of appearance and behavior, self-reported symptoms, mental health history, and current life circumstances. The views of other professionals, 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 rare specialist cases neuroimaging tests may be requested, but such 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. In addition, comorbidity is very common in psychiatric diagnosis, where the same person meets the criteria for more than one disorder. On the other hand, a person may have several different difficulties only some of which meet the criteria for being diagnosed. There may be specific problems with accurate diagnosis in developing countries. More structured approaches are being increasingly used to measure levels of mental illness.

List of mental disorders
The Diagnostic and Statistical Manual of Mental Disorders (DSM) is the American Psychiatric Association's standard reference for psychiatry which includes over 450 different definitions of mental disorders. The International Classification of Diseases (ICD) published by the World Health Organization (WHO) is the international standard system for classifying all medical diseases. It also includes a section on mental and behavioral disorders. The diagnostic criteria and information in the DSM and ICD are revised and updated with each new version. This list contains conditions which are currently recognised as mental disorders as defined by these two systems. There is disagreement in various fields of mental health care, including the field of psychiatry, over the definitions and criteria used to delineate mental disorders. Of concern to some professionals is whether certain mental disorders should be classified as 'mental illnesses' or whether they may be better described as neurological disorders, or in other ways.

Acute stress disorder
Adjustment disorder
Adolescent antisocial behavior
Adult antisocial behavior
Alcohol abuse
Alcohol dependence
Alcohol withdrawal
Alcoholic hallucinosis
Alzheimer's disease
Amnestic disorder
Amphetamine dependence
Anorexia nervosa
Anterograde amnesia
Antisocial personality disorder
Asperger syndrome
Attention deficit disorder
Attention deficit hyperactivity disorder
Avoidant personality disorder
Avoidant/restrictive food intake disorder

Barbiturate dependence
Benzodiazepine dependence
Benzodiazepine misuse
Benzodiazepine withdrawal
Binge eating disorder
Bipolar disorder
Bipolar I disorder
Bipolar II disorder
Body dysmorphic disorder
Borderline intellectual functioning
Borderline personality disorder
Brief psychotic disorder
Bulimia nervosa

Caffeine-induced anxiety disorder
Caffeine-induced sleep disorder
Cannabis dependence
Catatonic schizophrenia
Circadian rhythm sleep disorder
Cocaine dependence
Cocaine intoxication
Cognitive disorder
Communication disorder
Conduct disorder
Cotard delusion

Delirium tremens
Depersonalization disorder
Developmental coordination disorder
Diogenes Syndrome
Dissociative identity disorder

Ekbom's Syndrome (Delusional Parasitosis)
Enuresis (not due to a general medical condition)

Factitious disorder
Fregoli delusion
Fugue state

Ganser syndrome
Generalized anxiety disorder
General adaptation syndrome
Grandiose delusions
Gender identity disorder

Hallucinogen-related disorder
Hallucinogen persisting perception disorder
Histrionic personality disorder
Huntington's disease
Hypomanic episode

Intermittent explosive disorder

Korsakoff's syndrome

Lacunar amnesia

Major depressive disorder
Major depressive episode
Maladaptive daydreaming
Male chauvinism
Male erectile disorder
Manic episode
Mathematics disorder
Minor depressive disorder
Mixed episode
Mood disorder
Munchausen's syndrome

Narcissistic personality disorder
Neurodevelopmental disorder
Nicotine withdrawal
Night eating syndrome
Nightmare disorder

Obsessive-compulsive disorder (OCD)
Obsessive-compulsive personality disorder (OCPD)
Ondine's curse
Opioid dependence
Opioid-related disorder
Oppositional defiant disorder (ODD)
Orthorexia (ON)

Panic disorder
Paranoid personality disorder
Parkinson's Disease
Pathological gambling
Persecutory delusion
Personality disorder
Pervasive developmental disorder not otherwise specified (PDD-NOS)
Phencyclidine (or phencyclidine-like)-related disorder
Phobic disorder
Pica (disorder)
Phonological disorder
Physical abuse
Polysubstance-related disorder
Posttraumatic stress disorder (PTSD)
Premature ejaculation
Primary hypersomnia
Primary insomnia
Pseudologia fantastica
Psychogenic amnesia
Psychotic disorder

Reactive attachment disorder of infancy or early childhood
Recurrent brief depression
Relational disorder
Residual schizophrenia
Retrograde amnesia
Rumination syndrome

Schizoaffective disorder
Schizoid personality disorder
Schizophreniform disorder
Schizotypal personality disorder
Seasonal affective disorder
Sedative-, hypnotic-, or anxiolytic-related disorder
Selective mutism
Separation anxiety disorder
Sexual fetishism
Sexual masochism disorder
Sexual sadism disorder
Shared psychotic disorder
Sleep disorder
Seasonal affective disorder
Sleep terror disorder
Sleepwalking disorder
Sleep paralysis
Social anxiety disorder
Social phobia
Somatization disorder
Somatoform disorder
Specific phobia
Stereotypic movement disorder
Stockholm syndrome
Substance-related disorder

Tardive dyskinesia
Transient global amnesia
Transient tic disorder
Transvestic disorder