What is schizophrenia?

What causes schizophrenia?

Page last updated: May 2007

No single cause of schizophrenia has been identified, but several factors have been shown to be associated with its onset.

Men and women have an equal chance of developing this mental illness across the lifespan, although the onset for men is often earlier.

Genetic factors

A predisposition to schizophrenia can run in families. In the general population, only one percent of people develop it over their lifetime, but if one parent has schizophrenia, the children have a 10 percent chance of developing the condition - and a 90 percent chance of not developing it.

Biochemical factors

Certain biochemical substances in the brain are believed to be involved in schizophrenia, especially a neurotransmitter called dopamine. One likely cause of this chemical imbalance is the person's genetic predisposition to the illness. Complications during pregnancy or birth that cause structural damage to the brain may also be involved.

Family relationships

No evidence has been found to support the suggestion that family relationships cause the illness. However, some people with schizophrenia are sensitive to any family tension, which for them may be associated with recurrent episodes.


It is well recognised that stressful incidents often precede the onset of schizophrenia. These may act as precipitating events in vulnerable people.

People with schizophrenia often become anxious, irritable and unable to concentrate before any acute symptoms are evident. This can cause problems with work or study and relationships to deteriorate. Often these factors are then blamed for the onset of the illness when, in fact, the illness itself has caused the stressful event. It is not, therefore, always clear whether stress is a cause or a result of schizophrenia.

Alcohol and other drug use

Harmful alcohol and other drug use, particularly cannabis and amphetamine use, may trigger psychosis in people who are vulnerable to developing schizophrenia. While substance use does not cause schizophrenia, it is strongly related to relapse.

People with schizophrenia are more likely than the general population to use alcohol and other drugs, and this is detrimental to treatment.

A considerable proportion of people with schizophrenia have been shown to smoke, which contributes to poor physical health.