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Schizophrenia - Etiology

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The cause of schizophrenia is complex mix of genetics, risk factors, environmental factors, family dynamics in each individual case

Schizophrenia and drug use

The relationship between schizophrenia and drug use is complex, meaning that a clear causal connection between drug use and schizophrenia has been difficult to tease apart. There is strong evidence that using certain drugs can trigger either the onset or relapse of schizophrenia in some people. It may also be the case, however, that people with schizophrenia use drugs to overcome negative feelings associated with the commonly prescribed antipsychotic medication, and the disorder itself, where negative emotion, paranoia and anhedonia are all considered to be core features.


Schizophrenia can sometimes be triggered by heavy use of stimulant or hallucinogenic drugs, although some claim that a predisposition towards developing schizophrenia is needed for this to occur. There is also some evidence suggesting that people suffering schizophrenia but responding to treatment can have relapse because of subsequent drug use.

Drugs such as methamphetamine, ketamine, PCP and LSD have been used to mimic schizophrenia for research purposes, although this has now fallen out of favor with the scientific research community, as the differences between the drug induced states and the typical presentation of schizophrenia have become clear.

Hallucinogenic drugs were also briefly tested as possible treatments for schizophrenia by psychiatrists such as Humphry Osmond and Abram Hoffer in the 1950s. Ironically, it was mainly for this experimental treatment of schizophrenia that LSD administration was legal, briefly before its use as a recreational drug led to its criminalization.


There is increasing evidence that cannabis use can contribute to the onset of schizophrenia. Some studies suggest that cannabis is neither a sufficient nor necessary factor in developing schizophrenia, but that cannabis may significantly increase the risk of developing schizophrenia and may be, among other things, a significant causal factor. Nevertheless, some previous research in this area has been criticised as it has often not been clear whether cannabis use is a cause or effect of schizophrenia. To address this issue, a recent review of studies from which a causal contribution to schizophrenia can be assessed has suggested that cannabis doubles the risk of developing schizophrenia on the individual level, and may be responsible for up to 8% of cases in the population.48


It has been noted that the majority of people with schizophrenia (estimated between 75% and 90%) smoke tobacco. However, people diagnosed with schizophrenia have a much lower than average chance of getting and dying from lung cancer. While the reason for this is unknown, it may be because of a genetic resistance to the cancer, a side-effect of drugs being taken, or a statistical effect of increased likelihood of dying from causes other than lung cancer49.

It is argued that the increased level of smoking in schizophrenia may be due to a desire to self-medicate with nicotine. A recent study of over 50,000 Swedish conscripts found that there was a small but significant protective effect of smoking cigarettes on the risk of developing schizophrenia later in life.50 Whilst the authors of the study stressed that the risks of smoking far outweigh these minor benefits, this study provides further evidence for the 'self-medication' theory of smoking in schizophrenia and may give clues as to how schizophrenia might develop at the molecular level. Furthermore, many people with schizophrenia have smoked tobacco products long before they are diagnosed with the illness, and some groups advocate that the chemicals in tobacco have actually contributed to the onset of the illness and have no benefit of any kind


Considerable evidence indicates that stressful life events cause or trigger schizophrenia.[1] Childhood experiences of abuse or trauma have also been implicated as risk factors for a diagnosis of schizophrenia later in life.[2][3][4]

Evidence is also consistent that negative attitudes towards individuals with (or with a risk of developing) schizophrenia can have a significant adverse impact. In particular, critical comments, hostility, authoritarian and intrusive or controlling attitudes (termed 'high expressed emotion' by researchers) from family members have been found to correlate with a higher risk of relapse in schizophrenia across cultures.[5] It is not clear whether such attitudes play a causal role in the onset of schizophrenia, although those diagnosed in this way may claim it to be the primary causal factor. The research has focused on family members but also appears to relate to professional staff in regular contact with clients.[6] While initial work addressed those diagnosed as schizophrenic, these attitudes have also been found to play a significant role in other mental health problems.[7] This approach does not blame 'bad parenting' or staffing, but addresses the attitudes, behaviors and interactions of all parties. Some go as far as to criticise the whole approach of seeking to localise 'mental illness' within one individual - the patient - rather than his/her group and its functionality, citing a scapegoat effect.

Factors such as poverty and discrimination also appear to be involved in increasing the risk of schizophrenia or schizophrenia relapse, perhaps due to the high levels of stress they engender, or faults in diagnostic procedure/assumptions. Racism in society, including in diagnostic practices, and/or the stress of living in a different culture, may explain why minority communities have shown higher rates of schizophrenia than members of the same ethnic groups resident in their home country. The "social drift hypothesis" suggests that the functional problems related to schizophrenia, or the stigma and prejudice attached to them, can result in more limited employment and financial opportunities, so that the causal pathway goes from mental health problems to poverty, rather than, or in addition to, the other direction. Some argue that unemployment and the long-term unemployed and homeless are simply being stigmatised.

One particularly stable and replicable finding has been the association between living in an urban environment and schizophrenia diagnosis, even after factors such as drug use, ethnic group and size of social group have been controlled for.[8] A recent study of 4.4 million men and women in Sweden found an alleged 68%–77% increased risk of diagnosed psychosis for people living in the most urbanized environments, a significant proportion of which is likely to be described as schizophrenia.[9]

See also

References & Bibliography

  1. Day R, Nielsen JA, Korten A, Ernberg G, Dube KC, Gebhart J, Jablensky A, Leon C, Marsella A, Olatawura M et al (1987). Stressful life events preceding the acute onset of schizophrenia: a cross-national study from the World Health Organization. Culture, Medicine and Psychiatry, 11 (2), 123–205
  2. Harriet L. MacMillan, Jan E. Fleming, David L. Streiner, Elizabeth Lin, Michael H. Boyle, Ellen Jamieson, Eric K. Duku, Christine A. Walsh, Maria Y.-Y. Wong, William R. Beardslee. (2001) Childhood Abuse and Lifetime Psychopathology in a Community Sample. American Journal of Psychiatry,158, 1878-83.
  3. Schenkel, L.S., Spaulding, W.D., Dilillo, D., Silverstein, S.M. (2005) Histories of childhood maltreatment in schizophrenia: Relationships with premorbid functioning, symptomatology, and cognitive deficits. Schizophrenia Research
  4. Janssen I., Krabbendam L., Bak M., Hanssen M., Vollebergh W., De Graaf R., Van Os, J. (2004) Childhood abuse as a risk factor for psychotic experiences. Acta Psychiatrica Scandinavica, 109, 38-45.
  5. Bebbington P E, Kuipers E (1994) The predictive utility of expressed emotion in schizophrenia: an aggregate analysis. Psychological Medicine, 24, 707-718.
  6. Van Humbeeck G, Van Audenhove C. (2003) Expressed emotion of professionals towards mental health patients. Epidemiologia e Psychiatria Sociale, 12(4), 232-235. (full text)
  7. Wearden AJ, Tarrier N, Barrowclough C, Zastowny TR, Rahill AA. (2000) A review of expressed emotion research in health care. Clinical Psychology Review, 20, 633-66.
  8. Van Os J. (2004) Does the urban environment cause psychosis? British Journal of Psychiatry, 184 (4), 287–288.
  9. Sundquist K, Frank G, Sundquist J. (2004) Urbanisation and incidence of psychosis and depression: Follow-up study of 4.4 million women and men in Sweden. British Journal of Psychiatry, 184 (4), 293–298.

Key texts



  • Walker,Elaine, Kestler,Lisa, Bollini,Annie and Hochman,Karen M. (2004)­Schizophrenia: Etiology and Course. Annual Review of Psychology.Vol. 55: 401-430


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