Schizophrenia Causes

Possible causes of schizophrenia

The causes of mental illness are linked to several factors which can be summarised into three main groups:

Biological factors

  • which arise from physiology, biochemistry, genetic make-up and physical constitution and the drugs that they might abuse

Psychological factors

  • including the person's upbringing, emotional experiences and interactions with people

Social factors

  • that are associated with the person's present life situation and sociocultural influences


  • Exposure to stressors, both environmental and social may overwhelm a person's coping ability and may as a result contribute to the onset of mental illness.

No single cause of schizophrenia has been identified to date; there are most likely to be several contributing factors.  It is probable that there is an interaction between the consumer's biological vulnerability, stress or change in the environment and the consumer's ability to deal with these environmental factors in terms of their social skills and supports.  A less stressful environment may decrease the risk of onset in a person with a predisposition to schizophrenia or their relapse with another episode of the illness.

We know that schizophrenia is NOT caused by:

  • Domineering mothers or passive fathers
  • Poverty
  • Weakness of character or personality
  • Bad parenting
  • Sinful behaviour

Possible Contributing Factors:  

NB:  These are possible causal factors.  None, in their own right cause Schizophrenia.  They may, particularly in combination increase the risk of developing Schizophrenia.


Twin, family and adoptions studies suggest that genetic factors play an important role in the development of schizophrenia.  For example, the child of one parent with schizophrenia has about a 10 per cent chance of developing schizophrenia; if both parents have schizophrenia, the risk is increased to 40 per cent.  By comparison, the risk of schizophrenia in the general population is about one per cent.  The list below indicates the chances of developing schizophrenia during a life time:

  • General Population 1%
  • Brother or sister has schizophrenia 8-10%
  • One parent has schizophrenia 12-15%
  • paternal twin has schizophrenia 14%
  • Identical twin has schizophrenia 50%

Schizophrenia has a large number of genes implicated in its cause (like other disease such as high blood pressure).   It is likely that no single gene “causes” schizophrenia.  Rather there is a large number of genes that increase the risk of getting schizophrenia.   These genes are important in different aspects of the way the brain develops and the way brain cells communicate to each other.  If an individual has a large number of these genes and is placed in a stressful environment this makes getting schizophrenia more likely.   Some of these genes also play a part in other severe psychiatric disease such as bipolar disorder.  This is one of the reasons that it can be difficult to diagnose these illnesses – they really do overlap.


Possible environmental factors include obstetric complications, the mother’s exposure to influenza during pregnancy or starvation.  It has also been suggested that stress, trauma even migration can lead to the emergence of schizophrenia.  Family factors causing stress may affect the course of the illness but there is no convincing evidence that they have a causative role.

Neurodevelopmental Factors

Schizophrenia appears to be a neurodevelopmental disorder.   That is the changes that cause the illness have been occurring from the earliest stages of development even in utero, and may continue to influence the development of the brain over the first 25 years of life.   This also means that we could influence or change the likelihood of getting the illness by identifying these factors and intervening early.   At present we are unable to do this satisfactorily. 

Drug Misuse

Substance misuse, including cannabis, is important in the development of schizophrenia in some people.  It is well established that substance misuse may precipitate or worsen the symptoms and interfere in the treatment of a person with schizophrenia. 

Biochemical Factors

The neurodevelopmental and genetic factors that we described above have an effect upon the development of the brain and the expression or amounts of many brain chemicals and neurotransmitters.  Neurotransmitters (the substances that allow communication between nerve cells) have long been thought to be involved in the development of schizophrenia and many of the treatments for schizophrenia affect neurotransmitter function.  Although there are no definitive answers yet, this is a very active area of schizophrenia research.