Schizophrenia is a mental illness characterized by abnormal behavior, strange speech, and a decreased ability to understand reality.^[2] Other symptoms may include false beliefs, unclear or confused thinking, hearing voices that do not exist, reduced social engagement and emotional expression, and lack of motivation.^[2][3] People with schizophrenia often have additional mental health problems such as anxiety, depression, or substance-use disorders.^[11] Symptoms typically come on gradually, begin in young adulthood, and, in many cases, never resolve.^[3][6]

The causes of schizophrenia include environmental and genetic factors.^[5] Possible environmental factors include being raised in a city, cannabis use during adolescence, certain infections, the age of a person's parents, and poor nutrition during pregnancy.^[5][12] Genetic factors include a variety of common and rare genetic variants.^[13] Diagnosis is based on observed behavior, the person's reported experiences and reports of others familiar with the person.^[6][6][6]dissociative identity disorder with which it is often confused in public perception.^[14]

The mainstay of treatment is antipsychotic medication, along with counselling, job training, and social rehabilitation.^[2][5] It is unclear whether typical or atypical antipsychotics are better.^[15] In those who do not improve with other antipsychotics, clozapine may be tried.^[5] In more serious situations where there is risk to self or others, involuntary hospitalization may be necessary, although hospital stays are now shorter and less frequent than they once were.^[16]

About 0.3% to 0.7% of people are affected by schizophrenia during their lifetimes.^[9] In 2013, there were an estimated 23.6 million cases globally.^[17] Males are more often affected and onset is on average earlier in age.^[2] About 20% of people eventually do well, and a few recover completely.^[6] About 50% have lifelong impairment.^[18] Social problems, such as long-term unemployment, poverty, and homelessness, are common.^[6][19] The average life expectancy of people with the disorder is 10–25 years less than that of the general population.^[8] This is the result of increased physical health problems and a higher suicide rate (about 5%).^[9][20] In 2015, an estimated 17,000 people worldwide died from behavior related to, or caused by, schizophrenia.^[10]

People with schizophrenia may experience hallucinations (most reported are hearing voices), delusions (often bizarre or persecutory in nature), and disorganized thinking and speech. The last may range from loss of train of thought, to sentences only loosely connected in meaning, to speech that is not understandable known as word salad. Social withdrawal, sloppiness of dress and hygiene, and loss of motivation and judgment are all common in schizophrenia.^[21]

Distortions of self-experience such as feeling as if one's thoughts or feelings are not really one's own to believing thoughts are being inserted into one's mind, sometimes termed passivity phenomena, are also common.^[22] There is often an observable pattern of emotional difficulty, for example lack of responsiveness.^[23] Impairment in social cognition is associated with schizophrenia,^[24] as are symptoms of paranoia. Social isolation commonly occurs.^[25] Difficulties in working and long-term memory, attention, executive functioning, and speed of processing also commonly occur.^[9] In one uncommon subtype, the person may be largely mute, remain motionless in bizarre postures, or exhibit purposeless agitation, all signs of catatonia.^[26] People with schizophrenia often find facial emotion perception to be difficult.^[27] It is unclear if the phenomenon called "thought blocking", where a talking person suddenly becomes silent for a few seconds to minutes, occurs in schizophrenia.^[28][29]

About 30 to 50 percent of people with schizophrenia fail to accept that they have an illness or comply with their recommended treatment.^[30] Treatment may have some effect on insight.^[31]

People with schizophrenia may have a high rate of irritable bowel syndrome, but they often do not mention it unless specifically asked.^[32] Psychogenic polydipsia, or excessive fluid intake in the absence of physiological reasons to drink, is relatively common in people with schizophrenia.^[33]

Schizophrenia is often described in terms of positive and negative (or deficit) symptoms.^[34]Symptoms%20in%20the%20mind%3A%20an%20introduct]] not normally experience, but are present in people with schizophrenia. They can include delusions, disordered thoughts and speech, and tactile, auditory, visual, olfactory and gustatory hallucinations, typically regarded as manifestations of psychosis.^[35] Hallucinations are also typically related to the content of the delusional theme.^[36] Positive symptoms generally respond well to medication.^[36]

Negative symptoms are deficits of normal emotional responses or of other thought processes, and are less responsive to medication.^[21] They commonly include flat expressions or little emotion, poverty of speech, inability to experience pleasure, lack of desire to form relationships, and lack of motivation. Negative symptoms appear to contribute more to poor quality of life, functional ability, and the burden on others than positive symptoms do.^[18][37] People with greater negative symptoms often have a history of poor adjustment before the onset of illness, and response to medication is often limited.^[21][38]

The validity of the positive and negative construct has been challenged by factor analysis studies observing a three dimension grouping of symptoms.

Different terminology is used, but a dimension for hallucinations, a dimension for disorganization, and a dimension for negative symptoms are usually described.^[39]

Deficits in cognitive abilities are widely recognized as a core feature of schizophrenia.^[40][41][42] The extent of the cognitive deficits someone experiences is a predictor of how functional they will be, the quality of occupational performance, and how successful they will be in maintaining treatment.^[43] The presence and degree of cognitive dysfunction in people with schizophrenia has been reported to be a better indicator of functionality than the presentation of positive or negative symptoms.^[40] The deficits impacting the cognitive function are found in a large number of areas: working memory, long-term memory,^[44][45] verbal declarative memory,^[46] semantic processing,^[47] episodic memory,^[43] attention,^[18] learning (particularly verbal learning).^[44] Deficits in verbal memory are the most pronounced in someone with schizophrenia, and are not accounted for by deficit in attention. Verbal memory impairment has been linked to a decreased ability in those with schizophrenia to semantically encode (process information relating to meaning), which is cited as a cause for another known deficit in long-term memory.^[44] When given a list of words, healthy people remember positive words more frequently (known as the Pollyanna principle), but people with schizophrenia tend to remember all words equally regardless of their connotations, suggesting that the experience of anhedonia impairs the semantic encoding of the words.^[44] These deficits have been found in people before the onset of the illness to some extent.^[40][42][48] First-degree family members of those with schizophrenia and other high-risk people also show a degree of deficit in cognitive abilities, and specifically in working memory.^[48] A review of the literature on cognitive deficits in people with schizophrenia shows that the deficits may be present in early adolescence, or as early as childhood.^[40] The deficits which a person with schizophrenia presents tend to remain the same over time in most patients, or follow an identifiable course based upon environmental variables.^[40][44]

Although the evidence that cognitive deficits remain stable over time is reliable and abundant,^[43][44] much of the research in this domain focuses on methods to improve attention and working memory.^[44][45] Efforts to improve learning ability in people with schizophrenia using a high- versus low-reward condition and an instruction-absent or instruction-present condition revealed that increasing reward leads to poorer performance while providing instruction leads to improved performance, highlighting that some treatments may exist to increase cognitive performance.^[44] Training people with schizophrenia to alter their thinking, attention, and language behaviors by verbalizing tasks, engaging in cognitive rehearsal, giving self-instructions, giving coping statements to the self to handle failure, and providing self-reinforcement for success, significantly improves performance on recall tasks.^[44] This type of training, known as self-instructional (SI) training, produced benefits such as lower number of nonsense verbalizations and improved recall when distracted.^[44]

Late adolescence and early adulthood are peak periods for the onset of schizophrenia,^[9] critical years in a young adult's social and vocational development.^[49] In 40% of men and 23% of women diagnosed with schizophrenia, the condition manifested itself before the age of 19.^[50] The most general symptoms of schizophrenia tend to appear between ages 16 and 30.^[3][6] The onset of the disorder is usually between ages 18 and 25 for men and between 25 and 35 for women.^[51] To minimize the developmental disruption associated with schizophrenia, much work has recently been done to identify and treat the prodromal (pre-onset) phase of the disorder, which has been detected up to 30 months before the onset of symptoms.^[49] Those who go on to develop schizophrenia may experience transient or self-limiting psychotic symptoms^[52] and the non-specific symptoms of social withdrawal, irritability, dysphoria,^[53] and clumsiness before the onset of the disease.^[54] Children who go on to develop schizophrenia may also demonstrate decreased intelligence, decreased motor development (reaching milestones such as walking slowly), isolated play preference, social anxiety, and poor school performance.^[55][56][57]

A combination of genetic and environmental factors play a role in the development of schizophrenia.^[9][14] People with a family history of schizophrenia who have a transient psychosis have a 20–40% chance of being diagnosed one year later.^[58]

Estimates of the heritability of schizophrenia are around 80%, which implies that 80% of the individual differences in risk to schizophrenia is associated with genetics.^[59][60] These estimates vary because of the difficulty in separating genetic and environmental influences and some have labeled these estimates inaccurate.^[61][62] The greatest single risk factor for developing schizophrenia is having a first-degree relative with the disease (risk is 6.5%); more than 40% of monozygotic twins of those with schizophrenia are also affected.^[14] If one parent is affected the risk is about 13% and if both are affected the risk is nearly 50%.^[59] Results of candidate gene studies of schizophrenia have generally failed to find consistent associations,^[63] and the genetic loci identified by genome-wide association studies as associated with schizophrenia explain only a small fraction of the variation in the disease.^[64]

Many genes are known to be involved in schizophrenia, each of small effect and unknown transmission and expression.^[13][65] The summation of these effect sizes into a polygenic risk score can explain at least 7% of the variability in liability for schizophrenia.^[66] Around 5% of cases of schizophrenia are understood to be at least partially attributable to rare copy number variants (CNVs), including 22q11, 1q21 and 16p11.^[67] These rare CNVs increase the risk of someone developing the disorder by as much as 20-fold, and are frequently comorbid with autism and intellectual disabilities.^[67] There is a genetic relation between the common variants which cause schizophrenia and bipolar disorder, an inverse genetic correlation with intelligence and no genetic correlation with immune disorders.^[68]

The question of how schizophrenia could be primarily genetically influenced, given that people with schizophrenia have lower fertility rates, is a paradox.

It is expected that genetic variants that increase the risk of schizophrenia would be selected against due to their negative effects on reproductive fitness. A number of potential explanations have been proposed, including that alleles associated with schizophrenia risk confers a fitness advantage in unaffected individuals.^[69][70] While some evidence has not supported this idea,^[62] others propose that a large number of alleles each contributing a small amount can persist.^[5]

Environmental factors associated with the development of schizophrenia include the living environment, drug use, and prenatal stressors.^[9]

Maternal stress has been associated with an increased risk of schizophrenia, possibly in association with reelin.^[72] Maternal nutritional deficiencies, such as those observed during a famine, as well as maternal obesity have also been identified as possible risk factors for schizophrenia. Both maternal stress and infection have been demonstrated to alter fetal neurodevelopment through pro-inflammatory proteins such as IL-8 and TNF.^[73][74]

Parenting style seems to have no major effect, although people with supportive parents do better than those with critical or hostile parents.^[14] Childhood trauma, death of a parent, and being bullied or abused increase the risk of psychosis.^[75][76] Living in an urban environment during childhood or as an adult has consistently been found to increase the risk of schizophrenia by a factor of two,^[9][14] even after taking into account drug use, ethnic group, and size of social group.^[77] Other factors that play an important role include social isolation and immigration related to social adversity, racial discrimination, family dysfunction, unemployment, and poor housing conditions.^[14][78]

It has been hypothesized that in some people, development of schizophrenia is related to intestinal tract dysfunction such as seen with non-celiac gluten sensitivity or abnormalities in the intestinal flora.^[79] A subgroup of persons with schizophrenia present an immune response to gluten different from that found in people with celiac, with elevated levels of certain serum biomarkers of gluten sensitivity such as anti-gliadin IgG or anti-gliadin IgA antibodies.^[80]

About half of those with schizophrenia use drugs or alcohol excessively.^[81] Amphetamine, cocaine, and to a lesser extent alcohol, can result in a transient stimulant psychosis or alcohol-related psychosis that presents very similarly to schizophrenia.^[14][82] Although it is not generally believed to be a cause of the illness, people with schizophrenia use nicotine at much higher rates than the general population.^[83]

Alcohol abuse can occasionally cause the development of a chronic, substance-induced psychotic disorder via a kindling mechanism.^[84] Alcohol use is not associated with an earlier onset of psychosis.^[85]

Cannabis may be a contributory factor in schizophrenia, potentially causing the disease in those who are already at risk.^[12] The increased risk may require the presence of certain genes within an individual.^[12] Among those who are at risk of psychosis, it is associated with twice the rate.^[86]

Other drugs may be used only as coping mechanisms by people who have schizophrenia, to deal with depression, anxiety, boredom, and loneliness.^[81][87]

Factors such as hypoxia and infection, or stress and malnutrition in the mother during fetal development, may result in a slight increase in the risk of schizophrenia later in life.^[9] People diagnosed with schizophrenia are more likely to have been born in winter or spring (at least in the northern hemisphere), which may be a result of increased rates of viral exposures in utero.^[14] The increased risk is about five to eight percent.^[88] Other infections during pregnancy or around the time of birth including Toxoplasma gondi and Chlamydia, and some pathogens seropositivity are linked to an increase in risk.^[89] Viral infections of the brain during childhood are also linked to a risk of psychosis during adulthood.^[90]

While the mechanism of schizophrenia is unknown, a number of attempts have been made to explain the link between altered brain function and schizophrenia.^[9] One of the most common is the dopamine hypothesis, which attributes psychosis to the mind's faulty interpretation of the misfiring of dopaminergic neurons.^[9] Other possible mechanisms include glutaminergic neurotransmission and neurodevelopment. Frameworks have hypothesized links between these biological abnormalities and symptoms.^[91]

Abnormal dopamine signalling has been implicated in schizophrenia based on the usefulness of medications that effect the dopamine receptor and the observation that dopamine levels are increased during acute psychosis.^[92][93] Abnormalities in dopamine signalling have been hypothesized to underlie delusions.^[94][95][96] A decrease in D1 receptors in the prefrontal cortex may also be responsible for deficits in working memory.^{[97][98][99][100]}

Reduced NMDA receptor signalling is suggested by multiple lines of evidence. Studies demonstrate reduced NMDA receptor expression and NMDA receptor blockers mimic both schizophrenia symptoms and the physiological abnormalities associated with schizophrenia.^{[101][102][103]} Post-mortem studies consistently find that a subset of these neurons fail to express GAD67,^[104] in addition to abnormalities in morphology. The subsets of interneurons that are abnormal in schizophrenia are responsible for the synchronizing of neural ensembles that is necessary during working memory tasks, a process that is electrophysiologically reflected in gamma frequency (30–80 Hz) oscillations. Both working memory tasks and gamma oscillations are impaired in schizophrenia, which may reflect abnormal interneuron functionality.^{[104][105][106][107]}

Evidence suggest that schizophrenia has a neurodevelopmental component.

Before the onset of schizophrenia there is often impairments in cognition, social functioning, and motor skills.^[108] Furthermore, problems before birth such as maternal infection,^[109][110] maternal malnutrition and complications during pregnancy all increase risk for schizophrenia.^[73] Schizophrenia usually emerges 18-25, an age period that overlaps with certain stages of neurodevelopment that are implicated in schizophrenia.^[111]

Deficits in executive functions, such as planning, inhibition, and working memory, are pervasive in schizophrenia. Although these functions are dissociable, their dysfunction in schizophrenia may reflect an underlying deficit in the ability to represent goal related information in working memory, and to utilize this to direct cognition and behavior.^[112][113] These impairments have been linked to a number of neuroimaging and neuropathological abnormalities. For example, functional neuroimaging studies report evidence of reduced neural processing efficiency, whereby the dorsolateral prefrontal cortex is activated to a greater degree to achieve a certain level of performance relative to controls on working memory tasks. These abnormalities may be linked to the consistent post-mortem finding of reduced neuropil, evidenced by increased pyramidal cell density and reduced dentritic spine density. These cellular and functional abnormalities may also be reflected in structural neuroimaging studies that find reduced grey matter volume in association with deficits in working memory tasks.^[114]

Positive and negative symptoms have been linked to reduced cortical thickness in the superior temporal lobe,^[115] and orbitofrontal cortex, respectively.^[116] Anhedonia, traditionally defined as a reduced capacity to experience pleasure, is frequently reported in schizophrenia. However, a large body of evidence suggests that hedonic responses are intact in schizophrenia,^[117] and that what is reported to be anhedonia is a reflection of dysfunction in other processes related to reward.^[118] Overall, a failure of online maintenance and reward associativity is thought to lead to impairment in the generation of cognition and behavior required to obtain rewards, despite normal hedonic responses.^[119]

Bayesian models of brain functioning have been utilized to link abnormalities in cellular functioning to symptoms.^[120][121] Both hallucinations and delusions have been suggested to reflect improper encoding of prior expectations, thereby causing expectation to excessively influence sensory perception and the formation of beliefs. In canonical models of circuits that mediate predictive coding, hypoactive NMDA receptor activation, similar to that seen in schizophrenia, could theoretically result in classic symptoms of schizophrenia such as delusions and hallucinations.^[122][123]

Schizophrenia is diagnosed based on criteria in either the American Psychiatric Association's (APA) fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM 5) or the World Health Organization's International Statistical Classification of Diseases and Related Health Problems (ICD-10). These criteria use the self-reported experiences of the person and reported abnormalities in behavior, followed by a clinical assessment by a mental health professional. Symptoms associated with schizophrenia occur along a continuum in the population and must reach a certain severity and level of impairment before a diagnosis is made.^[14] As of 2013, there is no objective test.^[6]

In 2013, the American Psychiatric Association released the fifth edition of the DSM (DSM-5). To be diagnosed with schizophrenia, two diagnostic criteria have to be met over much of the time of a period of at least one month, with a significant impact on social or occupational functioning for at least six months. The person had to be suffering from delusions, hallucinations, or disorganized speech. A second symptom could be negative symptoms, or severely disorganized or catatonic behaviour.^[6] The definition of schizophrenia remained essentially the same as that specified by the 2000 version of DSM (DSM-IV-TR), but DSM-5 makes a number of changes.

The ICD-10 criteria are typically used in European countries; the DSM criteria are used in the United States and some other countries, and are prevailing in research studies.

The ICD-10 criteria put more emphasis on Schneiderian first-rank symptoms.

In practice, agreement between the two systems is high.^[128] The current proposal for the ICD-11 criteria for schizophrenia recommends adding self-disorder as a symptom.^[22]

If signs of disturbance are present for more than a month but less than six months, the diagnosis of schizophreniform disorder is applied. Psychotic symptoms lasting less than a month may be diagnosed as brief psychotic disorder, and various conditions may be classed as psychotic disorder not otherwise specified; schizoaffective disorder is diagnosed if symptoms of mood disorder are substantially present alongside psychotic symptoms. If the psychotic symptoms are the direct physiological result of a general medical condition or a substance, then the diagnosis is one of a psychosis secondary to that condition.^[6] Schizophrenia is not diagnosed if symptoms of pervasive developmental disorder are present unless prominent delusions or hallucinations are also present.^[6]

With the publication of DSM-5, the APA removed all sub-classifications of schizophrenia.^[129] The five sub-classifications included in DSM-IV-TR were:^[130][131]

The ICD-10 defines additional subtypes:^[130]

Psychotic symptoms may be present in several other mental disorders, including bipolar disorder,^[133] borderline personality disorder,^[134] drug intoxication, and drug-induced psychosis. Delusions ("non-bizarre") are also present in delusional disorder, and social withdrawal in social anxiety disorder, avoidant personality disorder and schizotypal personality disorder. Schizotypal personality disorder has symptoms that are similar but less severe than those of schizophrenia.^[6] Schizophrenia occurs along with obsessive-compulsive disorder (OCD) considerably more often than could be explained by chance, although it can be difficult to distinguish obsessions that occur in OCD from the delusions of schizophrenia.^[135] A few people withdrawing from benzodiazepines experience a severe withdrawal syndrome which may last a long time. It can resemble schizophrenia and be misdiagnosed as such.^[136]

A more general medical and neurological examination may be needed to rule out medical illnesses which may rarely produce psychotic schizophrenia-like symptoms, such as metabolic disturbance, systemic infection, syphilis, AIDS dementia complex, epilepsy, limbic encephalitis, and brain lesions. Stroke, multiple sclerosis, hyperthyroidism, hypothyroidism, and dementias such as Alzheimer's disease, Huntington's disease, frontotemporal dementia, and the Lewy body dementias may also be associated with schizophrenia-like psychotic symptoms.^[137] It may be necessary to rule out a delirium, which can be distinguished by visual hallucinations, acute onset and fluctuating level of consciousness, and indicates an underlying medical illness. Investigations are not generally repeated for relapse unless there is a specific medical indication or possible adverse effects from antipsychotic medication. In children hallucinations must be separated from typical childhood fantasies.^[6]

Prevention of schizophrenia is difficult as there are no reliable markers for the later development of the disorder.^[138] There is tentative evidence for the effectiveness of early interventions to prevent schizophrenia.^[139] There is some evidence that early intervention in those with a psychotic episode may improve short-term outcomes, but there is little benefit from these measures after five years.^[9] Attempting to prevent schizophrenia in the prodrome phase is of uncertain benefit and therefore as of 2009 is not recommended.^[140] Cognitive behavioral therapy may reduce the risk of psychosis in those at high risk after a year^[141] and is recommended in this group, by the National Institute for Health and Care Excellence (NICE).^[142] Another preventative measure is to avoid drugs that have been associated with development of the disorder, including cannabis, cocaine, and amphetamines.^[14]

The primary treatment of schizophrenia is antipsychotic medications, often in combination with psychological and social supports.^[9] Hospitalization may occur for severe episodes either voluntarily or (if mental health legislation allows it) involuntarily. Long-term hospitalization is uncommon since deinstitutionalization beginning in the 1950s, although it still occurs.^[16] Community support services including drop-in centers, visits by members of a community mental health team, supported employment^[143] and support groups are common. Some evidence indicates that regular exercise has a positive effect on the physical and mental health of those with schizophrenia.^[144] As of 2015 it is unclear if transcranial magnetic stimulation (TMS) is useful for schizophrenia.^[145]

The first-line psychiatric treatment for schizophrenia is antipsychotic medication,^[146] which can reduce the positive symptoms of psychosis in about 7 to 14 days.

Antipsychotics fail to significantly improve the negative symptoms and cognitive dysfunction.^[38][147] In those on antipsychotics, continued use decreases the risk of relapse.^[148][149] There is little evidence regarding effects from their use beyond two or three years.^[149] Use of anti-psychotics can lead to dopamine hypersensitivity increasing the risk of symptoms if antipsychotics are stopped.^[150]

The choice of which antipsychotic to use is based on benefits, risks, and costs.^[9] It is debatable whether, as a class, typical or atypical antipsychotics are better.^[15][151] Amisulpride, olanzapine, risperidone, and clozapine may be more effective but are associated with greater side effects.^[152] Typical antipsychotics have equal drop-out and symptom relapse rates to atypicals when used at low to moderate dosages.^[153] There is a good response in 40–50%, a partial response in 30–40%, and treatment resistance (failure of symptoms to respond satisfactorily after six weeks to two or three different antipsychotics) in 20% of people.^[38] Clozapine is an effective treatment for those who respond poorly to other drugs ("treatment-resistant" or "refractory" schizophrenia),^[154] but it has the potentially serious side effect of agranulocytosis (lowered white blood cell count) in less than 4% of people.^[9][14][155]

Most people on antipsychotics have side effects.

People on typical antipsychotics tend to have a higher rate of extrapyramidal side effects; some atypicals are associated with considerable weight gain, diabetes and risk of metabolic syndrome. This is most pronounced with olanzapine; risperidone and quetiapine are also associated with weight gain.^[152] Risperidone has a similar rate of extrapyramidal symptoms to haloperidol.^[152] It remains unclear whether the newer antipsychotics reduce the chances of developing neuroleptic malignant syndrome or tardive dyskinesia, a rare but serious neurological disorder.^[156]

For people who are unwilling or unable to take medication regularly, long-acting depot preparations of antipsychotics may be used to achieve control.^[157] They reduce the risk of relapse to a greater degree than oral medications.^[148] When used in combination with psychosocial interventions, they may improve long-term adherence to treatment.^[157] The American Psychiatric Association suggests considering stopping antipsychotics in some people if there are no symptoms for more than a year.^[149]

A number of psychosocial interventions may be useful in the treatment of schizophrenia including: family therapy,^[158] assertive community treatment, supported employment, cognitive remediation,^[159] skills training, token economic interventions, and psychosocial interventions for substance use and weight management.^[160] Family therapy or education, which addresses the whole family of a patient, may reduce relapses and hospitalizations.^[158] Evidence for the effectiveness of cognitive-behavioral therapy (CBT) in either reducing symptoms or preventing relapse is minimal.^[161][162] Evidence for metacognitive training is mixed with some reviews finding benefit and another not.^{[163][164][165]} Art or drama therapy have not been well-researched.^[166][167] Peer support, in which people with experiential knowledge of mental illness provide help to each other, is of unclear benefit in schizophrenia.^[168]

Schizophrenia has great human and economic costs.^[9] It results in a decreased life expectancy by 10–25 years.^[8] This is primarily because of its association with obesity, poor diet, sedentary lifestyles, and smoking, with an increased rate of suicide playing a lesser role.^[9][8][169] Antipsychotic medications may also increase the risk.^[8] These differences in life expectancy increased between the 1970s and 1990s.^[170]

Schizophrenia is a major cause of disability, with active psychosis ranked as the third-most-disabling condition after quadriplegia and dementia and ahead of paraplegia and blindness.^[171] Approximately three-fourths of people with schizophrenia have ongoing disability with relapses^[38] and 16.7 million people globally are deemed to have moderate or severe disability from the condition.^[172] Some people do recover completely and others function well in society.^[173] Most people with schizophrenia live independently with community support.^[9] About 85% are unemployed.^[5] Some evidence suggests that paranoid schizophrenia may have a better prospect than other types of schizophrenia for independent living and occupational functioning.^[36] In people with a first episode of psychosis a good long-term outcome occurs in 42%, an intermediate outcome in 35% and a poor outcome in 27%.^[175] Outcomes for schizophrenia appear better in the developing than the developed world.^[176] These conclusions have been questioned.^[177][178]

There is a higher than average suicide rate associated with schizophrenia. This has been cited at 10%, but a more recent analysis revises the estimate to 4.9%, most often occurring in the period following onset or first hospital admission.^[20][179] Several times more (20 to 40%) attempt suicide at least once.^[6][180] There are a variety of risk factors, including male gender, depression, and a high intelligence quotient.^[180]

Schizophrenia and smoking have shown a strong association in studies worldwide.^[181][182] Use of cigarettes is especially high in those diagnosed with schizophrenia, with estimates ranging from 80 to 90% being regular smokers, as compared to 20% of the general population.^[182] Those who smoke tend to smoke heavily, and additionally smoke cigarettes with high nicotine content.^[183] Some propose that this is in an effort to improve symptoms.^[184] Among people with schizophrenia use of cannabis is also common.^[81]

Schizophrenia affects around 0.3–0.7% of people at some point in their life,^[9] or 24 million people worldwide as of 2011.^[185] It occurs 1.4 times more frequently in males than females and typically appears earlier in men^[14]—the peak ages of onset are 25 years for males and 27 years for females.^[186] Onset in childhood is much rarer,^[187] as is onset in middle or old age.^[188]

Despite the prior belief that schizophrenia occurs at similar rates worldwide, its frequency varies across the world,^[6][189] within countries,^[190] and at the local and neighborhood level.^[191] This variation has been estimated to be fivefold.^[5] It causes approximately one percent of worldwide disability adjusted life years^[14] and resulted in 20,000 deaths in 2010.^[192] The rate of schizophrenia varies up to threefold depending on how it is defined.^[9]

In 2000, the World Health Organization found the percentage of people affected and the number of new cases that develop each year is roughly similar around the world, with age-standardized prevalence per 100,000 ranging from 343 in Africa to 544 in Japan and Oceania for men, and from 378 in Africa to 527 in Southeastern Europe for women.^[193] About 1.1% of adults have schizophrenia in the United States.^[194]

In the early 20th century, the psychiatrist Kurt Schneider listed the forms of psychotic symptoms that he thought distinguished schizophrenia from other psychotic disorders. These are called first-rank symptoms or Schneider's first-rank symptoms. They include delusions of being controlled by an external force, the belief that thoughts are being inserted into or withdrawn from one's conscious mind, the belief that one's thoughts are being broadcast to other people, and hearing hallucinatory voices that comment on one's thoughts or actions or that have a conversation with other hallucinated voices.^[195] Although they have significantly contributed to the current diagnostic criteria, the specificity of first-rank symptoms has been questioned. A review of the diagnostic studies conducted between 1970 and 2005 found that they allow neither a reconfirmation nor a rejection of Schneider's claims, and suggested that first-rank symptoms should be de-emphasized in future revisions of diagnostic systems.^[196] The absence of first-rank symptoms should raise suspicion of a medical disorder.^[22]

The history of schizophrenia is complex and does not lend itself easily to a linear narrative.^[197] Accounts of a schizophrenia-like syndrome are thought to be rare in historical records before the 19th century, although reports of irrational, unintelligible, or uncontrolled behavior were common. A detailed case report in 1797 concerning James Tilly Matthews, and accounts by Philippe Pinel published in 1809, are often regarded as the earliest cases of the illness in the medical and psychiatric literature.^[198] The Latinized term dementia praecox was first used by German alienist Heinrich Schule in 1886 and then in 1891 by Arnold Pick in a case report of a psychotic disorder (hebephrenia). In 1893 Emil Kraepelin borrowed the term from Schule and Pick and in 1899 introduced a broad new distinction in the classification of mental disorders between dementia praecox and mood disorder (termed manic depression and including both unipolar and bipolar depression).^[199]American%20madness%3A%20the%20rise%20and%20fal]] Kraepelin believed that erm, smouldering systemic or "whole body" disease process that affected many organs and peripheral nerves in the body but which affected the brain after puberty in a final decisive cascade.^[200] His use of the term "praecox" distinguished it from other forms of dementia such as Alzheimer's disease which typically occur later in life.^[201]Conditions%20in%20occup]]It is sometimes argued that the use of the term in 1852 by the French physician Bénédict Morel constitutes the medical discovery of schizophrenia. This account ignores the fact that there is little to connect Morel's descriptive use of the term and the independent development of the aecox* disease concept at the end of the nineteenth century.^[202]

The word schizophrenia—which translates roughly as "splitting of the mind" and comes from the Greek roots schizein (σχίζειν, "to split") and phrēn, phren- (φρήν, φρεν-, "mind")^[203]—was coined by Eugen Bleuler in 1908 and was intended to describe the separation of function between personality, thinking, memory, and perception. American and British interpretations of Bleuler led to the claim that he described its main symptoms as four A's: flattened affect, autism, impaired association of ideas, and ambivalence.^{[[204]](https://portal.issn.org/resource/ISSN/"Epistemological aspects of Eugen Bleuler's conception of schizophrenia in 1911")[205]} Bleuler realized that the illness was not a dementia, as some of his patients improved rather than deteriorated, and thus proposed the term schizophrenia instead. Treatment was revolutionized in the mid-1950s with the development and introduction of chlorpromazine.^[206]

In the early 1970s, the diagnostic criteria for schizophrenia were the subject of a number of controversies which eventually led to the operational criteria used today. It became clear after the 1971 US–UK Diagnostic Study that schizophrenia was diagnosed to a far greater extent in America than in Europe.^[207] This was partly due to looser diagnostic criteria in the US, which used the DSM-II manual, contrasting with Europe and its ICD-9. David Rosenhan's 1972 study, published in the journal Science under the title "On being sane in insane places", concluded that the diagnosis of schizophrenia in the US was often subjective and unreliable.^[208] These were some of the factors leading to the revision not only of the diagnosis of schizophrenia, but the revision of the whole DSM manual, resulting in the publication of the DSM-III in 1980.^[209]

The term schizophrenia is commonly misunderstood to mean that affected persons have a "split personality".

Although some people diagnosed with schizophrenia may hear voices and may experience the voices as distinct personalities, schizophrenia does not involve a person changing among distinct, multiple personalities; the confusion arises in part due to the literal interpretation of Bleuler's term "schizophrenia" (Bleuler originally associated schizophrenia with dissociation, and included split personality in his category of schizophrenia).^[210][211] Dissociative identity disorder (having a "split personality") was also often misdiagnosed as schizophrenia based on the loose criteria in the DSM-II.^{[211][212][213][214]} the illness.^[215]

In 2002, the term for schizophrenia in Japan was changed from seishin-bunretsu-byō (精神分裂病, lit. "mind-split disease") to tōgō-shitchō-shō (統合失調症, lit. "integration disorder") to reduce stigma.^[216] The new name was inspired by the biopsychosocial model; it increased the percentage of people who were informed of the diagnosis from 37 to 70% over three years.^[217] A similar change was made in South Korea in 2012.^[218] A professor of psychiatry, Jim van Os, has proposed changing the English term to "psychosis spectrum syndrome".^[219]

In the United States, the cost of schizophrenia—including direct costs (outpatient, inpatient, drugs, and long-term care) and non-health care costs (law enforcement, reduced workplace productivity, and unemployment)—was estimated to be $62.7 billion in 2002.^[220] The book and film A Beautiful Mind chronicles the life of John Forbes Nash, a mathematician who won the Nobel Prize for Economics and was diagnosed with schizophrenia.

People with severe mental illness, including schizophrenia, are at a significantly greater risk of being victims of both violent and non-violent crime.^[221] Schizophrenia has been associated with a higher rate of violent acts, but most appear to be related to associated substance abuse.^[222] Rates of homicide linked to psychosis are similar to those linked to substance misuse, and parallel the overall rate in a region.^[223] What role schizophrenia has on violence independent of drug misuse is controversial, but certain aspects of individual histories or mental states may be factors.^[224] About 11% of people in prison for homicide have schizophrenia and 21% have mood disorders.^[225] Another study found about 8-10% of people with schizophrenia had committed a violent act in the past year compared to 2% of the general population.^[225]

Media coverage relating to violent acts by people with schizophrenia reinforces public perception of an association between schizophrenia and violence.^[222] In a large, representative sample from a 1999 study, 12.8% of Americans believed that those with schizophrenia were "very likely" to do something violent against others, and 48.1% said that they were "somewhat likely" to.

Over 74% said that people with schizophrenia were either "not very able" or "not able at all" to make decisions concerning their treatment, and 70.2% said the same of money-management decisions.^[226] The perception of people with psychosis as violent has more than doubled in prevalence since the 1950s, according to one meta-analysis.^[227]

Schizophrenia is not believed to occur in non-human species^[228] but it may be possible to develop a pharmacologically induced nonhuman primate model of schizophrenia.^[229]

Research has found a tentative benefit in using minocycline to treat schizophrenia.^[230] Nidotherapy or efforts to change the environment of people with schizophrenia to improve their ability to function, is also being studied but there is not enough evidence yet to make conclusions about its effectiveness.^[231] Negative symptoms have proven a challenge to treat, as they are generally not made better by medication. Various agents have been explored for possible benefits in this area.^[232] There have been trials on drugs with anti-inflammatory activity, based on the premise that inflammation might play a role in the pathology of schizophrenia.^[233]