Dementia, depression or delirium?

Expert reviewer Dr Rahul Bhattacharya, Consultant Psychiatrist
Next review due July 2022

Dementia, depression and delirium are sometimes mistaken in older people, because the symptoms can be similar. Doctors working with older people sometimes refer to these conditions as ‘the three Ds’ for this reason. This page explains some of the similarities and differences between them, to help you if you’re concerned about a loved one.

Older man walking


‘Dementia’ refers to a set of symptoms. These include problems with thinking, language and daily activities. These symptoms can be caused by different underlying diseases, also called types of dementia. Alzheimer’s disease and vascular dementia are two common types of dementia.

Dementia gets worse over time. The symptoms can be subtle and difficult to spot at first, but eventually become more serious. The diagnosis is often confirmed by a combination of tests, assessments by doctors, and information from the person’s loved ones about their behaviour.

Sadly, there’s no cure for dementia. There are a handful of treatments that can slow down the progression in the early and middle stages of Alzheimer’s disease. Loved ones who are caring for a person with dementia at home can also provide valuable support. But caring can be physically and emotionally demanding, so carers need to take good care of themselves too. 


Depression is a psychological condition where you experience a persistent low mood. You may lose interest and pleasure in most activities.

Depression is more common among older people, but also harder to diagnose. That’s because certain physical illnesses, which older people are more prone to developing, may cause symptoms similar to depression. One example is thyroid problems, which can cause problems like a low mood and memory problems.

Depression and dementia

Some of the symptoms of dementia are similar to those of depression. Examples include:

  • being disoriented and withdrawn
  • feeling apathetic or uninterested
  • having difficulty concentrating

For older people who have depression, the symptoms may appear particularly close to those of dementia. Somebody who has had depression (or other mental health conditions) is at a higher risk of developing dementia. This may increase the chances of relatives or health professionals mistaking the early signs of dementia for an episode of depression.

When a person has dementia, it doesn’t mean they can’t also get depression. In fact, people with dementia are actually at higher risk of depression, with one-third of them developing the condition at some stage.

Having depression during dementia can sometimes be linked to someone’s worries about their diagnosis and how the condition will develop. This may explain why depression is more common with a type of dementia called vascular dementia, where someone is more likely to have insight and understanding of their condition.

Caring for an older person with depression

There are a number of options for treating someone with a diagnosis of depression. The doctor will choose the most suitable one based on the individual circumstances of the person. For older people with depression, there are some treatment options that may be more suitable than others. Older people are more likely to have physical illnesses alongside depression. An important part of tackling the depression will be to treat whatever physical illnesses the person has.

For mild or moderate depression, a doctor may prescribe a psychological therapy. This might be something like cognitive behavioural therapy (CBT) or counselling, which involve talking through problems with a health professional.

Sometimes a doctor may recommend self-help options to manage depression. This may be in the form of:

  • improving sleep routine
  • doing more exercise or activity, especially structured group exercise
  • eating well and avoiding alcohol
  • reading a leaflet or book, or an internet resource

For more serious depression, a doctor might prescribe medicines called antidepressants. However, some older people may not tolerate all antidepressant medicines well.

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Delirium is a syndrome (a set of symptoms) where someone is very confused and unable to focus their attention. They may also experience hallucinations, or have problems with movement or speech.

Delirium comes on very quickly, usually over a matter of hours or days. During an episode of delirium, the symptoms can fluctuate between being mild and severe.

There are three types of delirium:

  • hypoactive delirium, where someone is tired, lethargic, apathetic and withdrawn
  • hyperactive delirium, where someone is restless, agitated and may be aggressive
  • mixed delirium, where someone shows signs of both hypoactive and hyperactive delirium (this is the most common type)

Older people are more likely to experience delirium. Being very ill or frail, having a cognitive impairment (including dementia) or recovering from surgery, can also increase the risk. People who display only the quieter, more subdued symptoms of delirium may not be diagnosed as quickly as those who are more hyperactive, as the signs can be harder to notice.

Delirium can be caused be a wide range of underlying factors, including infections, high temperature and reactions to medicine. In most cases, there will be more than one underlying factor.

Delirium can increase the likelihood of other problems, including falls (because of problems with balance), reduced mobility, incontinence, malnutrition and dehydration. It’s important for health professionals to identify delirium as quickly as possible and treat any underlying causes.

Delirium and dementia

Some of the symptoms of dementia are similar to those of delirium, for example:

  • being confused and disoriented
  • becoming irritable, aggressive or paranoid (in hyperactive delirium)
  • being apathetic or withdrawn (in hypoactive delirium)

Because of these similarities, and the fact that older people are at risk of both conditions, it can be hard to tell the two apart.

Someone can have delirium and dementia at the same time. In fact, already having dementia puts someone at a higher risk of delirium. This means that an episode of delirium may be mistaken for someone’s dementia suddenly getting worse (or vice versa).

Delirium and depression

If someone has hypoactive delirium and they are apathetic and lethargic, this could be mistaken for depression. Very old people in particular may become quiet and withdrawn as a result of delirium, which may resemble depressive symptoms.

If someone has depression (with or without dementia), the doctor may prescribe antidepressants to treat it. However, some antidepressants (particularly tricyclic antidepressants – TCAs) can cause confusion and other delirium-like symptoms.

Caring for a person with delirium

Delirium is a serious problem and needs urgent attention. If your loved one has delirium, they will probably end up going to hospital so that doctors can monitor symptoms and address any underlying causes. In some specific circumstances they could be looked after outside of hospital, but this is rare.

When caring for a person with delirium, the main focus is on addressing the underlying cause. For example, someone with an infection will have that infection treated, or if they’re reacting to certain drugs, these drugs will be stopped. They should be well hydrated, in a well-ventilated environment with good lighting, and not constipated or in acute pain. Problems with seeing and hearing should also be checked for. Because underlying causes aren’t always easy to identify (and there may be more than one), there may be some ‘trial and error’ here. If your loved one hasn’t been admitted to hospital, steps can be taken to help reduce their confusion, especially if they are in a care home. Appropriate lighting and minimal background noise are helpful. It also helps to remind them of time and place; clocks and calendars are useful for this. If your loved one is in a care home, regular visits can also help with orientation.

If your loved one’s delirium leads to challenging behaviour, health professionals may use something called ‘de-escalation techniques’ to try and help them become calmer.

In more serious situations, where they may pose a risk to themselves or others, a doctor may give certain medicines to calm the person. The doctor will do this carefully, using low doses, monitoring your loved one closely, and not using the medicines for too long. Some of these medicines can’t be used if your loved one has a type of dementia called dementia with Lewy bodies, or if they have Parkinson’s disease.

Telling dementia, depression and delirium apart

If a doctor is trying to distinguish between dementia, delirium and depression in your loved one, you may be able to help. They may rely on your observations of their symptoms and behaviours.

There are some distinct features of the three conditions that can help you to try and work out what the problem might be if you are worried about a loved one.

  • A person with depression will not have their memory affected as badly as a person with dementia. Their thoughts will probably be more consistently negative, with feelings of low self-esteem and helplessness.
  • In general, delirium mainly affects a person’s attention, while dementia mainly affects their memory. A person with delirium will be more severely confused, and may be particularly agitated or lethargic, sometimes in a way that changes very quickly.
  • Another thing to look for is how quickly symptoms have appeared. Symptoms of dementia tend to come on very gradually. With depression they will come on more rapidly, typically over a number of weeks or months. With delirium they can be even more sudden: a matter of hours or days.
  • With delirium, symptoms are generally worse at night, when the person may be particularly confused or disoriented, or experience paranoia or hallucinations.

If the doctor thinks it may be delirium or depression, they’ll usually try to treat for these first before assessing or treating dementia.

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  • Reviewed by Graham Pembrey, Lead Editor, Bupa UK Health Content Team, June 2019
    Expert reviewer Dr Rahul Bhattacharya, Consultant Psychiatrist
    Next review due June 2022