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Schizophrenia - Causes

The exact causes of schizophrenia are unknown.

A mix of factors can make a person more likely to develop the condition. Factors such as:

  • physical
  • genetic
  • psychological
  • environmental

You may be prone to schizophrenia. A stressful or emotional life event might trigger a psychotic episode. But it's not known why some people develop symptoms and others don't.

Increased risk

There are a number of things that increase the chances of schizophrenia developing,

Genetics

Schizophrenia tends to run in families. Research suggests that no single gene is responsible.

It's more likely that combinations of genes make people more vulnerable. But having these genes doesn't mean you will develop schizophrenia.

Evidence that the disorder is partly inherited comes from studies of twins. Identical twins share the same genes.

If one identical twin develops schizophrenia, the other has a 1 in 2 chance. Even if they're not raised together.

In non-identical twins with different genetic make-ups, the other twin only has a 1 in 7 chance.

This is higher than in the general population, where the chance is about 1 in 100. It suggests genes aren't the only factor influencing the development of schizophrenia.

Brain development

There are some differences in the structure of the brain for people with schizophrenia.

These changes aren't seen in everyone with schizophrenia. They can occur in people who don't have a mental illness. But they suggest schizophrenia may partly be a disorder of the brain.

Neurotransmitters

Neurotransmitters are chemicals that carry messages between brain cells.

There's a connection between neurotransmitters and schizophrenia. Drugs that change the levels of neurotransmitters can relieve some of the symptoms.

A change in the level of two neurotransmitters may cause schizophrenia. These are dopamine and serotonin. An imbalance between the two may be the basis of the problem.

It is also thought that a change in the body's sensitivity to the neurotransmitters may be part of the cause.

Pregnancy and birth complications

If you have schizophrenia, you are more likely to have experienced complications before and during birth. For example:

  • a low birth weight
  • premature labour
  • a lack of oxygen (asphyxia) during birth

It may be that these things have a subtle effect on brain development.

History of traumatic events

Early traumas in life increase the risk of psychosis. These include:

  • child sexual abuse
  • physical abuse
  • bullying

But not everyone who has had early trauma will develop psychosis. Also, not everyone who has psychotic experiences has experienced childhood abuse.

Triggers

Triggers are things that can cause schizophrenia to develop in people who are at risk.

Stress

The main psychological triggers of schizophrenia are stressful life events, such as:

  • bereavement
  • losing your job or home
  • divorce
  • the end of a relationship
  • physical, sexual or emotional abuse

These kinds of experiences, although stressful, don't cause schizophrenia. But they can trigger its development in someone who is already vulnerable to it.

Drug abuse

Drugs don't directly cause schizophrenia. But drug misuse increases the risk of developing schizophrenia, or a similar illness.

Certain drugs may trigger symptoms of schizophrenia in people who are susceptible, particularly

  • cannabis
  • cocaine
  • LSD
  • amphetamines

Using amphetamines or cocaine can lead to psychosis. This can cause a relapse in people recovering from an earlier episode.

People under 15 who use cannabis regularly are up to 4 times more likely to develop schizophrenia by the age of 26. This is especially true for "skunk" and other more potent forms of the drug.

Content supplied by the NHS and adapted for Ireland by the HSE.

Page last reviewed: 15/03/2019
Next review due: 15/03/2022

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