Delirium - symptoms, diagnosis and treatment

Delirium is a serious but often treatable condition that can happen suddenly to someone who is unwell. It’s much more common in older people, especially those with dementia.

What is delirium?

Delirium is a change in a person’s mental state that happens suddenly over 1-2 days. It’s often the first sign that someone is becoming unwell.

Delirium can look different from one person to the next. Some people may become agitated or distressed while others are drowsy or withdrawn. The common feature to everyone who has delirium is that they become less responsive or alert to things happening around them.

Delirium is not the same as dementia, but they can look similar to someone who doesn’t know the person well. Dementia can make a person much more likely to have delirium. 

Delirium can have many different causes. The key to getting better is to find the causes of delirium and then try to resolve them. If this is done, most people will get better in a few days. However, some may take longer than this.

What are the symptoms of delirium?

The most important part of identifying delirium is noticing a sudden change in a person’s mental state – that they’re ‘not themselves’. Family, friends and carers are often best placed to do this because they know them well. It can be harder for a health professional who is seeing them for the first time.  

A person with delirium may:

  • be less alert and not respond to things happening around them
  • be easily distracted
  • be less aware of where they are, or what time it is (disorientation)
  • suddenly be less able to do something (for example, walking or eating)
  • speak less clearly or struggle to follow a conversation 
  • have sudden swings in mood or behaviour
  • have hallucinations – see or hear things that aren’t real
  • have delusions or become paranoid – strongly believing things that are not true.

Types of delirium

There are three main types of delirium: hyperactive (too active), hypoactive (not active enough) and mixed, where a person may change from one type to another during the course of a day. Among older people, including those with dementia, hypoactive and mixed delirium are most common.

Hyperactive delirium

A person with hyperactive delirium may:

  • seem restless or agitated, such as being unable to stay still or pacing 
  • resist or respond aggressively to personal care 
  • not understand where they are, or what time or day it is
  • seem unusually wary of other people
  • have delusions, such as thinking that people are trying to harm them  
  • have hallucinations, such as seeing someone next to the bed who isn’t really there.  

Hypoactive delirium

A person with hypoactive delirium may:

  • seem withdrawn, sluggish or tired
  • move around less
  • interact less with people around them
  • be unusually sleepy
  • struggle to stay focused when they’re awake
  • eat or drink less than usual.

It can be easy to miss hypoactive delirium because the person may just look tired or sleepy. They can easily go unnoticed when carers or healthcare workers are busy with other tasks. It’s only when someone tries to talk to them, or notices that they’re not themselves, that it becomes clear something is wrong.

Mixed delirium

A person with mixed delirium has symptoms of hyperactive delirium at times and symptoms of hypoactive delirium at other times. They switch between these symptoms during the course of a day, or from one day to the next. For example, they could be very agitated at one time and then later become very drowsy.

How is delirium different from dementia?

Delirium is not the same as dementia, although they can have similar symptoms . For a healthcare professional seeing a person for the first time, it can sometimes be difficult to tell the difference.


  • develops slowly (months or years)
  • gets worse over time
  • symptoms tend to be consistent from day to day
  • is a long-term health condition.


  • develops suddenly (1-2 days)
  • gets better quickly with the right treatment
  • symptoms can change a lot from hour to hour
  • is an urgent medical problem.

There may be a few exceptions to some of these differences, but they are true for most people. 

An important exception is when a person has dementia with Lewy bodies (DLB). This type of dementia has many of the same symptoms as delirium. It can be hard to tell the difference without knowing the person well, such as how long they’ve been having symptoms for.

Other symptoms of dementia

Dementia can cause a number of different symptoms. Here we explain some of these changes and suggest practical ways to manage them.


How is delirium diagnosed?

It’s really important that delirium is diagnosed quickly. It may cause severe health problems if it isn’t treated and the person’s delirium becomes more severe and prolonged.

The most important part of delirium being diagnosed is someone noticing that the person is not themselves, or that they’re acting strangely. This could be anyone who knows them well, such as a spouse or family member if they’re living at home, a carer or nurse if they’re living in a care home, or a healthcare professional or visitor if they’re in hospital. A doctor or nurse should then assess the person’s mental state as soon as possible.

It's very common for delirium to be missed or thought to be something else. Using a screening tool, such as a 4AT (the 4 A's test), can help to identify delirium more accurately.

The 4AT is a short set of simple questions that measure:

  • alertness – whether the person is drowsy or agitated
  • awareness – for example, their age or date of birth, or where they are
  • attention – the ability to stay focused on a mental task
  • acute change – if symptoms seem to come and go. 

It takes around two minutes to do a 4AT. The more mistakes a person makes with these simple tests, the more likely it is that they have delirium.

If a person has dementia and then develops delirium, a health professional meeting them for the first time may not be able to see that their problems with memory and thinking are much worse than usual. Their delirium symptoms may be thought to be part of their dementia.

Once a person has been diagnosed with delirium, healthcare professionals will try to work out what is causing it. This will do a physical examination to check for pain or other health problems. They may order further tests, such as blood tests, x-rays or other scans. This is important because the only way to treat delirium is to resolve the health problem that’s causing it.

Who gets delirium and why? 

Delirium is common, particularly among older people in hospital. It’s usually the reaction of the brain to a separate problem, such as:

  • pain
  • infection
  • having a major operation with general anaesthetic
  • physical injury, such as a bone fracture or head injury
  • poor nutrition or dehydration
  • constipation (not pooing) or urinary retention (not peeing)
  • low levels of blood oxygen
  • effects of medication
  • abnormal metabolism (for example, low levels of salts or sugar in the blood)
  • organ failure.

These health problems make it hard for the brain to work properly. This causes the symptoms of delirium.

Often there is more than one cause, which is why it’s so important to do a thorough examination when someone has delirium. All of the causes need to be treated for the person to get better.

Risk factors for delirium

Anyone can get delirium, but some people are more likely to develop it. These factors put people at higher risk:

  • having dementia – this is the biggest single risk factor for delirium
  • being older than 65
  • being frail or having multiple medical conditions
  • poor hearing or vision
  • being in an unfamiliar or disorientating environment
  • being sleep deprived
  • not being able to sit up or move around
  • taking certain medications, particularly those that cause drowsiness 
  • having already had delirium in the past.

These aren’t usually enough to cause delirium by themselves. However, they do make it more likely. They also make it harder for the brain to recover quickly.

With the right care, delirium can often be prevented. When a person comes into hospital or a care home, staff may check to see if they are at risk of delirium. If they are, they can put measures in place to help prevent it from happening.

What treatment and support is there for delirium?

Delirium is treated by resolving the health problems that have caused it. Once this is done, it’s important to make conditions as ideal as possible for the person’s brain to recover.

Some causes of delirium can be treated very quickly. Others may take several days or more to get better – for example, if they have a serious infection. However, the symptoms of delirium will usually improve once its causes are found and treated. 

A supportive and calm environment can also help someone recover from delirium. Healthcare professionals, family and friends can all help a person by: 

  • talking calmly in short clear sentences
  • reminding them where they are and who you are 
  • bringing familiar objects from home, such as photographs 
  • helping them to eat and drink regularly
  • making sure glasses and hearing aids are clean and working properly, and that they are wearing them
  • setting up a 24-hour clock and calendar that they can see clearly
  • helping them get into a healthy sleep routine 
  • providing reassurance if they have distressing hallucinations or delusions
  • supporting them to get up and about, as soon as it’s safe to do so
  • not taking them to new environments that are unfamiliar, busy or confusing.  

Medications to reduce hallucinations, delusions or aggressive behaviour should be considered only if the person poses a risk of harm to themselves or others, or if their symptoms are causing them severe distress. In either case a doctor may try a low dose of a sedative or an antipsychotic for a few days. 

Recovering from delirium

For many people the symptoms of delirium usually improve in a few days, once the underlying causes have been treated. 

However, some people don’t make a quick or full recovery and may still be having problems with memory and thinking several weeks or even months after becoming unwell. This is particularly common in older people who have had delirium after a major operation.

Having prolonged and severe delirium over several weeks can increase a person’s risk of developing dementia. This doesn’t mean that delirium causes dementia. But if someone was already having problems with memory and thinking, having delirium may speed up their decline so they develop dementia sooner than they would have done otherwise.

When a person leaves hospital after having had delirium, they may need more care and support than they did before. They may have trouble doing the everyday tasks that they were able to do before they became unwell. 

The clinical team at the hospital can provide useful advice on how to care for the person while they recover, as well as arranging for health and social care professionals to provide extra care and support if required.   

Dementia Support Line
Our dementia advisers are here for you.
Dementia Support Forum
Visit our online community to get advice, share experiences, connect.