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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.
New sudden 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- Changes in alertness: restless and agitated, or unusually quiet, withdrawn and sleepy.
- Fluctuating symptoms: 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- Hypoactive delirium is the quiet form: sleepy, withdrawn, flat, saying little. It is the most common form and the easiest to miss. A person dozing peacefully can look settled while being seriously unwell.
- Mixed delirium swings between the two, sometimes within a single day.
New drowsiness matters as much as new agitation. If a normally alert person is unusually sleepy but wakes and responds, report it urgently. If they are hard to wake, barely responding or cannot be roused, get emergency help now. In hospital, use the call bell and tell a nurse immediately; outside hospital, call the local emergency number immediately (999 in the UK).
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 is dependent. This can cause alcohol-withdrawal delirium, sometimes with severe agitation, hallucinations or seizures, and needs immediate hospital treatment
- Dehydration
- Constipation
- 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.
Delirium can affect anyone, at any age. Some things make it more likely once a trigger arrives: being older, having dementia, frailty, several long-term illnesses, poor hearing or sight, and having had delirium before.
How common is it?
older people in hospital have delirium at some point in their stay.
cases seen in hospital were already under way when the person arrived. Most delirium starts at home or in a care home.
patients in intensive care develop delirium. On a ventilator (breathing machine), around 7 in 10 do.
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 paediatric delirium in babies, children or young people; see the Resources page for UK and Vanderbilt 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: questions about age, date of birth, place and the current year, the months of the year backwards, and a rating of 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 are usually the best at noticing change, which is why what you tell the staff carries real weight.
If no one has said the word delirium and you suspect it, ask directly: “Could this be delirium?”
How is delirium treated?
Treatment means finding and treating every cause. A confirmed bacterial infection may need antibiotics; other infections do not. Dehydration may need fluids, a problem medicine may need to be stopped or changed, and pain and constipation should be treated.
Alongside that comes steady, practical care: 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, alongside treating 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.
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
Is delirium the same as dementia?
No. Delirium appears over hours or days and in most cases improves. Dementia develops over months or years and is nearly always permanent. The two are connected: dementia is the strongest risk factor for delirium. The differences, explained.
How long does delirium last?
A few days is typical. But delirium can last weeks, sometimes months, especially in people with dementia or after a severe illness. Recovery is usually gradual rather than a single morning when everything is back to normal. More on recovery.
Will they get back to normal?
Many people return fully to their old selves. Some do not; memory and concentration can remain below what they were before the illness, particularly in older people and those with dementia. Doctors cannot predict this well for any one person. Time, rehabilitation, sleep, food and drink all help.
Did we cause this? Should we have spotted it sooner?
No. Delirium comes from illness, injury, surgery, medicines and the brain’s own vulnerability. Even in hospital, with trained staff present around the clock, a large share of delirium is missed. There is no mistake to find.
Why are they bright in the morning and worse at night?
Fluctuation is part of the condition. Mental functioning in delirium rises and falls over hours, and evenings and nights are usually the low point. A clear spell in the afternoon does not mean the delirium has gone. Judge progress across days, not hours.
Can a urine infection cause delirium?
A genuine urinary tract infection can contribute to delirium. But delirium alone, a positive urine dipstick or bacteria in the urine does not prove a urinary tract infection in an older person. Clinicians should look for urinary or other signs of infection and consider other causes. Bacteria in the urine without symptoms often do not need antibiotics.
Why aren’t the doctors giving them something to cure it?
Because no drug has been shown to treat delirium itself. Treatment means finding and treating the triggers, together with practical, human care. Staff should first address reversible causes of distress and use calm de-escalation. A clinician may consider an antipsychotic only for severe distress or risk of harm, at the lowest appropriate dose for the shortest possible time.
Can delirium happen at home?
Yes, often. Around two thirds of the delirium seen in hospital patients began before they arrived. New sudden confusion needs medical assessment now. Contact the urgent or emergency medical service where the person is. In England, call 999 or go to A&E. In Scotland, contact the GP urgently if open; otherwise phone NHS 24 on 111. Outside the UK, follow local health-service guidance. What to do now.
- Delirium is a sudden change in mental functioning, arriving over hours or days, with a physical cause behind it.
- It affects about 1 in 4 older people in hospital, and it can affect anyone.
- The quiet, sleepy form is the most common and the most missed.
- Treatment means finding and treating all the triggers, plus steady practical care. No drug treats delirium itself.
- New sudden confusion needs medical assessment now. Do not wait to see if it settles.
The information on this site follows the research literature and current UK national guidance. The guidance links below are UK-based; outside the UK, follow the guidance used by your local health service. The main sources are:
- SIGN 157: Risk reduction and management of delirium (Scottish national guideline).
- NICE CG103: Delirium: prevention, diagnosis and management (updated 2023).
- NHS: Sudden confusion (delirium) and NHS inform: Delirium.
- UKHSA: Diagnosis of urinary tract infections.
- NICE NG108: Decision-making and mental capacity, NICE CG100: Alcohol-use disorders, and the MHRA reminder on haloperidol risks in delirium.
See Resources and helplines for more, including the SIGN booklet written for patients and carers.
If the change is happening now, here is exactly what to do.