Psychosis - Causes 

Causes of psychosis 

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Media last reviewed: 06/09/2013

Next review due: 06/09/2015

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The causes of psychosis have three main classifications:

  • psychosis caused by psychological (mental) conditions
  • psychosis caused by general medical conditions
  • psychosis caused by substances, such as alcohol or drugs

These three classifications are described in more detail below.

Psychological causes

The following conditions have been known to trigger psychotic episodes in some people:

  • schizophrenia – a chronic (long-term) mental health condition that causes hallucinations and delusions
  • bipolar disorder – previously called manic depression, bipolar disorder affects your moods, which can swing from one extreme to another
  • severe stress or anxiety
  • severe depression – feelings of extreme sadness that last a long time (including postnatal depression, which some women experience after having a baby)
  • lack of sleep

The underlying psychological cause will often influence the type of psychotic episode someone experiences. For example, a person with bipolar disorder is more likely to have delusions of grandeur, whereas someone with depression or schizophrenia is more likely to develop paranoid delusions (read more about the symptoms of psychosis).

General medical conditions

The following medical conditions have been known to trigger psychotic episodes in some people:

  • HIV and AIDS – a virus that attacks the body's immune system (the body’s natural defence against illness and infection)
  • malaria – a tropical disease spread by infected mosquitoes
  • syphilis – a bacterial infection usually passed through sexual contact
  • Alzheimer's disease – the most common form of dementia that causes a decline of mental abilities, such as memory and reasoning
  • Parkinson's disease – a chronic condition that affects the way the brain co-ordinates body movements, including walking, talking and writing
  • hypoglycaemia – an abnormally low level of sugar (glucose) in the blood
  • lupus – a condition where your immune system attacks healthy tissue
  • Lyme disease – a bacterial infection spread to humans by infected ticks
  • multiple sclerosis – a condition of the central nervous system (the brain and spinal cord) 
  • brain tumour – a growth of cells in the brain that multiply in an abnormal and uncontrollable way


Alcohol and drug misuse can trigger a psychotic episode. A psychotic episode can also be triggered if you suddenly stop taking a drug or drinking alcohol after using for a long time. This is known as withdrawal.

You can also experience psychosis after drinking large amounts of alcohol or if you are high on drugs.

Drugs known to trigger psychotic episodes include:

  • cocaine
  • amphetamine (speed)
  • methamphetamine (crystal meth)
  • mephedrone (MCAT or miaow)
  • MDMA (ecstasy)
  • cannabis
  • LSD (acid)
  • psilocybins (magic mushrooms)
  • ketamine

In rare situations, psychosis can also occur as a side effect of some types of medication, or as a result of an overdose of that medication.

One example is levodopa, a medication used to treat Parkinson's disease, but any medicine that acts on the brain can cause psychosis with an overdose.

Never stop taking a prescribed medication unless advised to do so by your GP or another qualified healthcare professional responsible for your care. See your GP if you are experiencing psychotic side effects because of taking a medication.

The brain

There has been a great deal of research looking at how psychosis affects the brain and conversely how changes in the brain can trigger symptoms of psychosis.

A summary of the research is provided below.

Grey matter

Research has revealed that during a psychotic episode several physical and biological changes occur in the brain.

The results of magnetic resonance imaging (MRI) scans have shown some people with a history of psychosis may have less grey matter than the average member of the general public. Grey matter is the part of the brain responsible for processing thoughts. MRI scans use a strong magnetic field and radio waves to take images of the inside of the body.

This research has led to scientists suggesting  repeated episodes of psychosis may actually cause physical damage to the brain. However, further research is required to confirm this.

Alternatively, both the reduction of grey matter and a history of psychosis could both be symptoms of an underlying condition not yet identified.


Researchers also believe that dopamine plays an important role in psychosis.

Dopamine is a neurotransmitter, one of many chemicals the brain uses to transmit information from one brain cell to another. Dopamine is associated with how we feel something is significant, important or interesting.

In people with psychosis, it is thought levels of dopamine in their brain rise too high. The excess dopamine interrupts specific pathways of the brain responsible for some of its most important functions, such as:

  • memory
  • emotion
  • social behaviour
  • self-awareness

Disruption to these important brain functions may explain the symptoms of psychosis.

Evidence for the role of dopamine in psychosis comes from several sources, including brain scans, and the fact that medications known to reduce the effects of dopamine in the brain also reduce symptoms of psychosis. However, illegal drugs known to increase levels of dopamine in the brain, such as cannabis, cocaine and amphetamines, can trigger psychosis.

Page last reviewed: 28/05/2012

Next review due: 28/05/2014


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The 2 comments posted are personal views. Any information they give has not been checked and may not be accurate.

DNAR said on 14 July 2012

Prescribed sleeping tablets, can change the chemical balance in the brain and cause horrific psychosis, triggering mental illness. But you have no comeback on a Doctor.

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UnhappyWithPHO said on 17 June 2012

Remember doctors can trigger psychosis, depression or worsen an undiagnosed mild depression often turning them severe, through prescription medication. They often don't acknowledge this and prescribe more of the same or group, often past the recommended max usage, whilst also increasing the medication.

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