What is psychosis?

What is psychosis?

The word psychosis describes a set of symptoms that include delusions (believing something that is unlikely to be true – that members of a secret society are conspiring to hurt you, for example), hallucinations (hearing voices, for example) and confused and disturbed thinking.

People who have a serious mental illness such as schizophrenia, bipolar disorder, schizoaffective disorder and psychotic depression experience some or all of the symptoms of psychosis. People who have some types of personality disorder can also experience these symptoms.

When these symptoms are experienced as part of a mental illness, mental health professionals say people are having a psychotic 'episode'. Psychotic episodes can vary in length: they can last for just a few days; they can continue indefinitely until they are treated; the symptoms can come and go.

When people have a psychotic episode, they are often unaware that they are unwell. They believe that what they are worrying about is actually happening to them – that they really are being followed, that their life is at risk, that they are being threatened, for instance. Mental health professionals call this ‘lack of insight’.

The symptoms of psychosis can also occur as a result of a physical health problem or disease. Urinary tract, chest or other infections, particularly in older people, can cause delirium, which can give rise to the symptoms of psychosis. People who have brain diseases such as Parkinson's disease, or dementia (see Older people page), or some types of epilepsy, may experience the symptoms of psychosis. The symptoms can also occur as a result of a brain tumour. Regular and excessive consumption of alcohol and illicit drugs can prompt psychotic symptoms. Sometimes psychotic experiences can be triggered by severe stress or anxiety, by sleep deprivation, or as a side effect of some medication.

It is best to get advice and treatment for the symptoms of psychosis as soon as people start experiencing them. Talk to your GP who can make a referral to the appropriate specialist services. Most NHS mental health trusts now run early intervention services especially for young people who are having experiences that may be the precursor of a psychotic episode (see Early intervention services page), or who are experiencing psychosis for the first time.

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Delusions and paranoia

Delusions are strong beliefs that are unlikely to be true. However, a person who has psychosis firmly believes them to be true, and as a result may say things that are strange, or behave in an odd way.

Often, people will believe that other people or organisations are out to get them, are spying on them or watching them, are trying to trick them, hurt them or even kill them. These paranoid delusions can be very frightening for the person who is unwell (see Paranoia page).

Sometimes people believe they have a special power or authority – that they are able to control other people’s thoughts, for example. Sometimes people have religious delusions – they may believe they are the mother or son of God for example. Sometimes people think they are someone historically important, or a celebrity – they may believe they are related to the royal family, or that they are a film star, for example. These sorts of beliefs are called 'grandiose ideas'. They can make people feel more cheerful and are not always distressing in themselves. However, the fact that no one else recognises how important they are may cause distress, and sometimes anger.

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Confused and disturbed thoughts

People may have disturbed and confused thoughts. Their thinking may speed up or slow down, and their mind may be full of different and random ideas.

Their jumbled thinking may be reflected in the way they speak – they may talk very quickly, without stopping, and without listening, or they may suddenly stop talking mid-sentence, or refuse to talk at all. They may say things that don’t make sense, or randomly switch from one subject matter to another. If they stop speaking suddenly, it may be that they have lost their train of thought, or their mind has gone blank. Sometimes people invent new words, or string words together in an unusual and confusing way.

Because of this muddled thinking, it may be difficult to follow what a person is saying, and hard to have an ordinary conversation with them.

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People may have hallucinations – see, hear, smell, taste or feel things that are not there. They might see people or objects that no one else can see, for example, or feel insects crawling on their skin.

People who experience the symptoms of psychosis because they have a mental illness such as schizophrenia commonly hear voices. These voices are entirely real to the person who is hearing them, so he or she may talk back and hold a conversation with them. Voices may say upsetting, critical, cruel and frightening things to, or about, the individual and this can be very distressing.

Some voices tell people what to do – and can sometimes dictate harmful or dangerous actions. Most people try to resist these aggressive commands, but often feel they must obey because they believe the voices are powerful and they fear what will happen to them if they disobey. These kinds of threatening voices are particularly likely to be distressing.

Imaging techniques have allowed researchers to see what happens inside the brain when people are hearing voices. The reason people who hear voices think they are real is because they hear them through the same system in the brain that everyone uses to hear external speech. They therefore experience their own thoughts as spoken words coming from the outside world.

The most common psychotic symptoms experienced by people who have Parkinson's disease are visual hallucinations – seeing things that aren't there. People may see friends and relatives, pets and other animals, or buildings and places that mean something to them. Sometimes what they see appears to be reduced in size, or transparent.

People who have dementia with Lewy bodies (DLB) very often regularly experience convincing and intense visual hallucinations. They often see people, children or animals: a typical hallucination is to see adults or children coming through the walls.

Lewy bodies are build-ups of particular proteins in nerve cells in the brain. They are found in the brains of people with this type of dementia and in the brains of people with Parkinson's disease (they are called Lewy bodies after the neurologist who first identified them). 

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Change of behaviour

The symptoms of psychosis may feel emotionally overwhelming. Delusions and hallucinations take over the way people see the world and become their reality. As a result, people who experience these symptoms may appear to be different – they may not appear to be the same person they were previously. They may become very excited or agitated and suspicious of other people. Or they may become miserable and withdrawn, refuse to see people and lose interest in everything they previously did. They may neglect their self-care. They may lose concentration and become distraught at not being able to deal with, or stop, what it happening to them.

It is important to remember psychosis can be very frightening for the person who is experiencing the symptoms. If the symptoms are severe, people can find it impossible to tell the difference between the experiences they are having and reality, to think logically or talk about how they are feeling, or to put their strange thoughts, emotions and fears in context. 



This page was last updated 21 February 2013
Links checked 5 July 2016


Understanding psychosis and schizophrenia: why people sometimes hear voices, believe things that others find strange, or appear out of touch with reality, and what can help

This report was published by the British Psychological Society's Division of Clinical Psychology at the end of November 2014.

It is written for people who have experienced psychosis, their friends, families, policymakers and journalists, and explains what is currently known about psychosis and schizophrenia. The report's authors include Professor Elizabeth Kuipers, who led the development of this website and other contributors to mentalhealthcare.org.uk – Professor Daniel Freeman, Dr Emmanuelle Peters and Professor Mike Slade.

Download the report