Delirium, Dementia, and Depression: How to Tell the Difference
Delirium, dementia, and depression are three different conditions that can look remarkably alike for individuals in midlife and later life. The fastest way to tell them apart is to consider how quickly the change occurred in your partner, friend, or family member, whether their attention is affected, and what has happened to their mood.
Delirium usually develops over hours or days and fluctuates. Dementia develops gradually over months or years. Depression often develops over weeks and shows up in mood, motivation, and memory retrieval rather than in attention or alertness.
These three conditions are sometimes called the three Ds of older adult mental health. They overlap, they can raise the risk of each other, and all three can be present in the same person at the same time (Downing et al., 2013).
Getting the distinction right matters, because the responses are so different. Delirium is a medical situation that needs same-day attention. Depression is highly treatable with psychological therapy at any age. Dementia calls for a different kind of psychological support and planning.
What the research tells us
Delirium comes on acutely, fluctuates through the day, and is marked by inattention and altered awareness. It is never a normal part of ageing (Wilson et al., 2020).
Delirium is common. Around one in four older medical patients in Australian hospitals are affected, and it is frequently missed, particularly when the person becomes drowsy, withdrawn, slow to respond, or says very little (hypoactive delirium) rather than if they experience agitation, restlessness, irritability, or hallucinations (hyperactive delirium) (Australian Commission on Safety and Quality in Health Care, 2021).
Dementia has a gradual onset and a slow course. Attention, alertness, and orientation are relatively preserved until later in the illness (Downing et al., 2013).
Depression in later life is more likely to present with physical complaints, sleep problems, irritability, or loss of interest than with someone saying they feel sadness (Downing et al., 2013).
Memory difficulties in depression tend to be problems retrieving information. In dementia and delirium, the difficulty affects both storing and retrieving information (Downing et al., 2013).
Older adults are more likely to raise concerns about low mood with their GP than with any other health professional (Downing et al., 2013).
Depression is one of fourteen modifiable risk factors for dementia identified by the 2024 Lancet Commission, and it can also be an early sign of cognitive change rather than only a cause (Livingston et al., 2024).
Psychological therapy works in later life. Cognitive behavioural therapy has strong evidence for depression across age groups and settings (Cuijpers et al., 2023), and psychotherapeutic interventions reduce depressive symptoms in community-dwelling older adults (Morgado et al., 2024).
What is delirium and how do you recognise it?
Delirium is a sudden change in attention, awareness, and thinking, caused by something physical going on in the body.
Common triggers include infection, dehydration, constipation, pain, low oxygen, alcohol withdrawal, surgery, and medication changes. Often several factors combine (Wilson et al., 2020).
The signature features are speed and fluctuation. Someone who was themselves last week is not themselves today, and they may be clearer in the morning and confused by evening.
Delirium takes three forms. The ‘loud version’ (hyperactive delirium), with agitation, restlessness, or hallucinations, gets noticed. The ‘quiet version’ (hypoactive delirium), with drowsiness, withdrawal, and slowed responses, is the one most often missed. Many people show a mix of both (Downing et al., 2013).
Signs worth acting on: new confusion over hours or days, difficulty holding attention in conversation, disorientation to time or place, seeing or hearing things that are not there, a reversed sleep pattern, or unusual drowsiness.
What to do: contact the GP the same day, or present to an emergency department if the change is marked. Delirium is treated by finding and treating the cause. Bringing someone's glasses and hearing aids, keeping familiar people close, and restoring routine all help (Wilson et al., 2020).
Recovery is usually possible, but it can be slower than families expect. Full clearing may take weeks to months, well after the original illness has resolved (Downing et al., 2013).
What is dementia and how does it differ from delirium?
Dementia is a progressive change in thinking, memory, language, or judgement that gradually affects everyday function.
It is an umbrella term rather than a single condition. More than one hundred different conditions can cause dementia, and Alzheimer's disease is the most common of them, which is why the two terms are often used interchangeably. We unpack that in our article, are dementia and Alzheimer's the same thing?
The onset is slow, with neurodegeneration starting around 20 years before the first signs of change are noticed Reiman, Quiroz, Fleisher, Chen et al., 2012; Villemagne, Burnham, Bourgeat, & Brown et al., 2013). Change is measured in months and years rather than hours and days, and, unlike in delirium, alertness, attention, and orientation are relatively well preserved until quite late in the illness (Downing et al., 2013).
Early signs of dementia often include repeating questions, losing the thread of familiar tasks, word-finding difficulty, letting go of previous routines and activities, misplacing household items such as the car keys, withdrawing from complicated situations or social situations, minor car accidents involving late responses, or a change in judgement around money and spending.
Dementia and delirium are closely linked. Having dementia raises the risk of developing delirium during an acute illness, and an episode of delirium raises the risk of later cognitive decline (Downing et al., 2013).
This is why a sudden worsening in someone who already has dementia should never be assumed to be "the dementia progressing". It is often delirium, and it is often treatable.
If you are thinking about brain health more broadly, our article on modifiable risk factors for dementia covers what the current evidence supports.
What does depression look like in midlife and later life?
Depression in later life often arrives without the word "depressed" ever being used.
People will often describe tiredness, aches, poor sleep, appetite change, irritability, or a flat sense that nothing is worth doing. Some will actively deny feeling low when asked directly (Downing et al., 2013).
Concentration and memory can suffer badly enough that people, and sometimes their families, assume dementia is starting. The pattern is usually different. In depression, the information is stored but harder to reach, and people are often acutely aware of and distressed by their memory lapses.
Depression is common in later life, but it is not a normal or inevitable response to ageing, loss, or illness. Treating it as expected is one of the main reasons it goes untreated (Downing et al., 2013).
Sleep is worth taking seriously in its own right. Persistent insomnia is associated with a substantially increased risk of developing major depression in older adults (Downing et al., 2013).
Where low mood is bound up with being overlooked, retired from, or written off, our article Age Is Not the Problem. Ageism Is. may be a useful companion read.
How can you tell delirium, dementia, or depression apart at home?
One way to start, is by looking for any patterns that could help a GP act quickly.
Ask about speed. Hours to days points towards delirium. Months to years points towards dementia. Weeks, often after a loss, health scare, or major change, points towards depression.
Ask about attention. Can the person follow a conversation, or do they drift, lose the thread, and need constant redirection? Marked inattention and fluctuating alertness point towards delirium.
Ask about mood. Persistent low mood, loss of pleasure, hopelessness, guilt, or withdrawal point towards depression.
Ask about awareness. People with depression often complain loudly about their memory. People with dementia more often minimise or are unaware of the change, while family members are the ones who are worried.
Ask what else changed. A new medication, a recent hospital admission, a recent infection, a fall, surgery, dehydration, or alcohol withdrawal makes delirium much more likely.
Write down what you notice, with dates. A short written timeline is one of the most useful things you can hand a GP.
Can someone have more than one of the three d’s at the same time?
Yes, and it is common.
Delirium, dementia, and depression overlap and each increases the risk of the others developing (Downing et al., 2013). Someone can have long-standing depression, be developing dementia, and be delirious from a urinary tract infection all at once.
This highlights the need for a GP assessment rather than settling for the first explanation that seems to fit.
Where does psychological support fit in?
Diagnosis of delirium and dementia sits with your GP and the medical specialists they refer to. That is the right starting point, and it usually involves a physical examination, blood tests, a review of medications, and a cognitive screen, with possible referral to a geriatrician for further assessment.
Psychological support is most useful alongside that process, and it focuses on the parts medicine does not always reach.
At Upside Stories, that includes evidence-based online psychological therapy for depression and anxiety in midlife and later life, support for adjusting to a recent diagnosis, and support for carers when a friend or family member lives with dementia or similar chronic illness. Our Carers' Compass program is built for that situation.
You can book a free 20-minute consultation to talk through whether therapy is the right fit right now.
Frequently asked questions
Do I need a GP referral to see a clinical psychologist at Upside Stories? No. You can book directly without a referral. A referral matters only if you want a Medicare rebate.
How do I get a Medicare rebate? Ask your GP whether a Mental Health Treatment Plan is appropriate for you. Your GP will consider whether you have a diagnosed mental health condition, such as depression, an adjustment disorder, an anxiety disorder, or a trauma-related condition, and whether you are likely to benefit from structured psychological support. Our referral assistance page sets out what to bring and what to ask.
Is memory loss just a normal part of getting older? While some slowing in recall and word-finding is a normal part of ageing, new difficulty with familiar everyday tasks, or a change that others around you have noticed, is worth raising with a GP rather than waiting.
Can depression be mistaken for dementia? It can, in both directions. Depression can impair concentration and memory enough to look like early dementia, and early dementia can present with apathy and withdrawal that look like depression. Careful GP assessment over time, rather than a single appointment, is usually what separates them.
If it turns out to be delirium, will it go away? Delirium usually improves once the underlying cause is treated, although full recovery can take weeks to months rather than days (Downing et al., 2013). Prompt medical attention gives the best chance of a good outcome.
Can psychological therapy help if my parent or partner is the one who is unwell? Yes. Family carers carry a significant emotional load, and support for carers is one of the areas we focus on. We support carers of all ages, from those in their 20s with ageing parents, through midlife and older age. You do not need to wait until you are struggling to book.
Can psychological therapy help with dementia risk? Indirectly, yes. Depression, social isolation, physical inactivity, and alcohol use are among the modifiable risk factors identified by the 2024 Lancet Commission, and psychological therapy can support change (Livingston et al., 2024).
Ready to talk it through?
If you are worried about your own memory or mood, or about someone you love, a conversation is a reasonable place to start.
Upside Stories offers online therapy across Australia, focusing on midlife, later life, and family carers.
References & reading
Australian Commission on Safety and Quality in Health Care. (2021). Delirium clinical care standard. Australian Government. https://www.safetyandquality.gov.au/standards/clinical-care-standards/delirium-clinical-care-standard
Cuijpers, P., Miguel, C., Harrer, M., Plessen, C. Y., Ciharova, M., Ebert, D., & Karyotaki, E. (2023). Cognitive behavior therapy vs. control conditions, other psychotherapies, pharmacotherapies and combined treatment for depression: A comprehensive meta-analysis including 409 trials with 52,702 patients. World Psychiatry, 22(1), 105–115. https://doi.org/10.1002/wps.21069
Downing, L. J., Caprio, T. V., & Lyness, J. M. (2013). Geriatric psychiatry review: Differential diagnosis and treatment of the 3 D's, delirium, dementia, and depression. Current Psychiatry Reports, 15(6), 365. https://doi.org/10.1007/s11920-013-0365-4
Livingston, G., Huntley, J., Liu, K. Y., Costafreda, S. G., Selbæk, G., Alladi, S., Ames, D., Banerjee, S., Burns, A., Brayne, C., Fox, N. C., Ferri, C. P., Gitlin, L. N., Howard, R., Kales, H. C., Kivimäki, M., Larson, E. B., Nakasujja, N., Rockwood, K., … Mukadam, N. (2024). Dementia prevention, intervention, and care: 2024 report of the Lancet standing Commission. The Lancet, 404(10452), 572–628. https://doi.org/10.1016/S0140-6736(24)01296-0
Morgado, B., Silva, C., Agostinho, I., Brás, F., Amaro, P., Lusquinhos, L., Silva, M. R., Fonseca, C., Albacar-Riobóo, N., & Guedes de Pinho, L. (2024). Psychotherapeutic interventions for depressive symptoms in community-dwelling older adults: A systematic review with meta-analysis. Healthcare, 12(24), 2551. https://doi.org/10.3390/healthcare12242551
Reiman, E. M., Quiroz, Y. T., Fleisher, A. S., Chen, K., Velez-Pardo, C., Jimenez-Del-Rio, M., Fagan, A. M., Shah, A. R., Alvarez, S., Arbelaez, A., Giraldo, M., Acosta-Baena, N., Sperling, R. A., Dickerson, B., Stern, C. E., Tirado, V., Munoz, C., Reiman, R. A., Huentelman, M. J., … Lopera, F. (2012). Brain imaging and fluid biomarker analysis in young adults at genetic risk for autosomal dominant Alzheimer's disease in the presenilin 1 E280A kindred: A case-control study. Lancet Neurology, 11(12), 1048–1056. https://doi.org/10.1016/S1474-4422(12)70228-4
Villemagne, V. L., Burnham, S., Bourgeat, P., Brown, B., Ellis, K. A., Salvado, O., Szoeke, C., Macaulay, S. L., Martins, R., Maruff, P., Ames, D., Rowe, C. C., & Masters, C. L., for the Australian Imaging Biomarkers and Lifestyle (AIBL) Research Group. (2013). Amyloid β deposition, neurodegeneration, and cognitive decline in sporadic Alzheimer's disease: A prospective cohort study. Lancet Neurology, 12(4), 357–367. https://doi.org/10.1016/S1474-4422(13)70044-9
Wilson, J. E., Mart, M. F., Cunningham, C., Shehabi, Y., Girard, T. D., MacLullich, A. M. J., Slooter, A. J. C., & Ely, E. W. (2020). Delirium. Nature Reviews Disease Primers, 6(1), 90. https://doi.org/10.1038/s41572-020-00223-4
