What is delirium?

Delirium is a sudden change in how a person thinks and responds. They may become confused, very sleepy, agitated or anxious. Some people see things that are not there or strongly believe things that are not true.

Families often put it simply: “They are not themselves.”

Unlike dementia, which develops over months or years, delirium appears within hours or days. It usually means that illness, injury or a change in medication has disrupted how the brain works.

Delirium (acute confusion) needs medical assessment now. Treating the cause early can make the delirium less severe and speed up recovery. If you think someone may have delirium now, go straight to what to do now.

The common signs

How delirium looks varies from episode to episode, but there are common features you can watch out for:

• Sudden confusion: the person might lose track of where they are or what time it is.
• Trouble paying attention: they may not be able to follow a conversation in the usual way. You might notice them being easily distracted, staring blankly, or appearing not to hear you.
• Changes in alertness: restless and agitated, or unusually quiet, withdrawn and sleepy.
• Symptoms that change: the confusion comes and goes, and is often worse at night.
• Hallucinations and delusions: seeing or hearing things that are not there (hallucinations), or strongly believing things that are not true (delusions).

The three forms

Doctors describe delirium by how it changes alertness and behaviour.

• Hyperactive delirium is the restless form: agitated, pacing, pulling at drips, sometimes suspicious or angry. This is the form most people picture, and it is the less common one.
• Hypoactive delirium can involve reduced activity and alertness. See the question below about unusual sleepiness and withdrawal.
• Mixed delirium swings between the two, sometimes within a single day.

Hyperactive

Restless and agitated. May pace, pull at drips, or be suspicious or angry. The less common form.

Hypoactive

Quiet, sleepy and withdrawn. Says little and responds slowly. Often missed.

Mixed

Swings between the two, sometimes within a single day.

Can delirium make someone very sleepy or withdrawn?

Yes. This can be hypoactive delirium: the person may say little, respond slowly, eat less or seem unusually sleepy. It is often missed. A sudden change needs urgent medical assessment. If the person is hard to wake or barely responding, get emergency help now. In hospital or a care home, alert staff immediately; at home, call your local emergency number.

What causes delirium?

Delirium is usually caused by something changing in the body, or a change in medication, that disrupts how the brain works. Common triggers include:

• Infections, such as chest infections or a symptomatic urinary tract infection
• Medication changes: starting new medicines, or suddenly stopping certain medicines
• Suddenly reducing or stopping alcohol in someone who depends on it can cause alcohol withdrawal. This can include delirium, severe restlessness, seeing or hearing things that are not there, or seizures, and needs immediate hospital treatment
• Too little fluid in the body
• Difficulty passing stools
• Pain that is not controlled
• Surgery
• Unfamiliar environments, such as the noise and disruption of a hospital ward

Often more than one trigger is acting at the same time, and good treatment means finding all of them, not just the first. Can a UTI cause confusion, and what if antibiotics have not helped?

Can anyone get delirium?

Yes. Delirium can affect anyone, at any age. Some things make delirium more likely. These include older age, dementia, less strength and ability to recover from illness, several long-term illnesses, poor hearing or sight, and having had delirium before.

How common is it?

This website focuses mainly on delirium in older people outside intensive care, although much of the information also applies in an ICU. For more specific ICU delirium information, see Vanderbilt’s ICU Delirium information for patients and families, which covers delirium in intensive care, ventilators, how families can help, and recovery afterwards. This is a US resource, so follow advice from the person’s own clinical team and local health service guidance. The site does not cover delirium in babies, children or young people; see the Resources page for specialist information.

Delirium is not rare, and it is nothing to be ashamed of. Millions of families face it across the world every year.

How is delirium diagnosed?

There is no blood test or scan for delirium. The diagnosis rests on one change above all: the person is different from their normal self, and the change arrived quickly.

Doctors and nurses use short bedside tests to help. Hospitals around the world use the 4AT, which takes about two minutes. It asks about age, date of birth, place and the current year, the months of the year backwards, and alertness. (The 4AT was designed by this site’s author with colleagues; it is free to use and has been validated in more than 30 studies.) The 4AT also asks whether there has been a recent change in mental functioning. Family members may notice changes from normal and can give staff useful information.

Depending on the hospital and setting, staff may use other tools, such as the Confusion Assessment Method (CAM), or CAM-ICU in intensive care. These assessments help the clinical team make a diagnosis. Families do not need to choose or carry out the test.

If no one has said the word delirium and you suspect it, ask directly: “Could this be delirium?”

Doctors also need to find out what is causing the symptoms. Some illnesses can cause delirium; others can cause symptoms that look similar. If the pattern is unusual or no clear cause is found, further assessment or specialist advice may be needed from the start. Read more about reviewing the diagnosis and possible causes.

How is delirium treated?

Treatment means looking for and treating the underlying cause or causes. A confirmed bacterial infection may need antibiotics; other infections do not. Too little fluid in the body may need fluids, a problem medicine may need to be stopped or changed, and pain and difficulty passing stools should be treated.

Steady, practical care is also important: regular drinks and meals, help to get up and moving, glasses and hearing aids on, good sleep at night, and familiar faces at the bedside. These measures are part of treatment while the team treats the underlying causes.

No drug has been shown to treat delirium itself. Staff should first look for reversible causes of distress and use calm verbal and non-verbal de-escalation. If distress remains severe or someone is at risk of harm, a clinician may consider an antipsychotic at the lowest appropriate dose for the shortest possible time. Haloperidol must not be used in people with Parkinson’s disease or dementia with Lewy bodies and has important heart and neurological risks. Antipsychotics do not shorten delirium.

What can happen after delirium?

Many people recover fully, though recovery often takes longer than families expect: weeks, sometimes months. Some people are left with memory, thinking or everyday skills below what they were before.

Studies of older people compared those who had delirium with people of similar age and health who did not. Those who had delirium were about twice as likely to die in the following two years. They were also more likely to move into a care home. On average, their memory and thinking were worse months and years later.

These figures are averages across large groups, so they are not a forecast for any one person. Part of the link may be because people who had delirium were more unwell to begin with. Studies try to allow for this.

Delirium is a serious condition. It can contribute to death through complications and difficulty recovering from illness. It is also often a sign that the person is seriously unwell. Many people recover, but some remain unwell or die despite treatment. Ask the team what they expect for this person and what is being done to treat the causes and prevent complications.

Someone who has had delirium once is more likely to have it again with the next illness or operation. Make sure the word delirium is in the hospital letter, and mention it before any future operation.

More: Can someone die from delirium?, After delirium: recovery and what to expect, Does delirium lead to dementia? and Will they remember anything about the delirium?

Can delirium be prevented?

Often, yes. Hospital prevention programmes that keep people drinking, eating, moving, sleeping and wearing their glasses and hearing aids reduce the number of cases by around a third. The same simple things lower the risk at home. Prevention lowers the risk; nothing removes it entirely, and delirium is never anyone’s fault.

Common questions

What do “acute confusion”, “acute confusional state” and “sudden confusion” mean?

“Acute” means that the change has developed recently, often over hours or days. Staff may use “acute confusion” or “acute confusional state” when describing delirium. “Sudden confusion” is another term for delirium, used on the NHS website, for example. Ask what diagnosis they mean and what is being done to find the causes. Delirium (acute confusion) needs medical assessment now; follow Get help now.

If the change is happening now, get help now.

All questions families ask