Differences Between Delirium and Dementia

Delirium and dementia are conditions that can be confusing, both to experience and to distinguish. Both can cause memory loss, poor judgment, a decreased ability to communicate, and impaired functioning. While the question of delirium vs dementia may seem difficult to answer, there are many differences between the two, including the following:

Older gentleman playing a puzzle game
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Dementia: Dementia typically begins slowly and is gradually noticed over time. If the person who's being evaluated is unknown to you, getting a report of their usual functioning is key.

Delirium: Delirium is usually a sudden change in a condition. One day, your loved one is doing fine, and the next, she may be very confused and unable to get dressed. Delirium is also known as acute confusional state, with the key being that it is acute, or sudden.


Dementia: The cause of dementia is typically a disease such as Alzheimer's, vascular dementia, lewy body dementia, frontotemporal dementia or a related disorder.

Delirium: Delirium is usually triggered by a specific illness, such as a urinary tract infection, pneumonia, dehydration, illicit drug use, or withdrawal from drugs or alcohol. Medications that interact with each other can also cause delirium, so make sure your physician knows all of the medications, supplements, and vitamins you're taking, even if they're natural substances.


Dementia: Dementia is generally a chronic, progressive disease that is incurable. (There are some reversible causes of dementia symptoms such as vitamin B12 deficiency, normal pressure hydrocephalus, and thyroid dysfunction).

Delirium: Delirium can last for a couple of days to even a couple of months. Delirium is almost always temporary if the cause is identified and treated.

Communication Abilities

Dementia: People with dementia may have difficulty finding the right words, and the ability to express themselves gradually deteriorates as the disease progresses.

Delirium: Delirium may significantly and uncharacteristically impair someone's ability to speak coherently or appropriately.

Attention Span and Memory

Dementia: A person's level of alertness is typically not affected until the late stages of Alzheimer's, whereas memory is significantly affected throughout the disease.

Delirium: In delirium, the opposite is true. Memory functioning is usually less affected in delirium but the ability to focus and maintain attention to something or someone is very poor.

Activity Level

Dementia: Dementia tends to not affect a person's activity level until the later stages.

Delirium: People with delirium are often either overly active (hyper and restless) or under-active (lethargic and less responsive) compared to usual functioning.


Dementia: There are currently a handful of medications approved by the Food and Drug Administration (FDA) to treat Alzheimer's disease, the most common type of dementia. Those medications don't cure dementia but sometimes can slow the progression of the symptoms, including memory loss, poor judgment, behavioral changes and more.

FDA Approves New Medication for Alzheimer's

In June 2021, the FDA approved Aduhelm (aducanumab) for treating patients with Alzheimer’s disease. Aduhelm is the first new drug approved to treat the disease since 2003 as well as the first to specifically target amyloid-beta, the protein researchers widely believe to play a role in the development of Alzheimer's.

Delirium: Delirium requires immediate treatment by a physician. Since it's usually caused by a physical illness or infection, medications such as antibiotics often resolve the delirium.

Delirium in People With Dementia

Distinguishing between delirium or dementia is important; however, a more difficult task may be identifying delirium in someone who already has dementia. According to a study by Fick and Flanagan, approximately 22% of older adults in the community with dementia develop delirium. However, that rate skyrockets to 89% for those who have dementia and are hospitalized.

Knowing how to identify delirium in someone who is already confused is critical for appropriate treatment and a faster recovery. Delirium superimposed on someone with dementia also is connected with a more than double mortality risk compared to those with delirium or dementia alone.

Delirium Signs to Look For

  • Increased agitation
  • Unusually resistive to care
  • Falls
  • Catastrophic reactions
  • Decreased communication
  • Inattention
  • Fluctuating alertness

A Word From Verywell

Understanding the difference between delirium and dementia can be helpful in identifying if your loved one needs to see the doctor immediately, or if he should be evaluated at an appointment that's scheduled within a few weeks. Be sure to report any signs of delirium, especially a sudden change in functioning or health, to the physician for evaluation and prompt treatment.  

13 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. The Mayo Clinic. Delirium.

  3. Hugo J, Ganguli M. Dementia and cognitive impairment: epidemiology, diagnosis, and treatmentClin Geriatr Med. 2014;30(3):421–442. doi:10.1016/j.cger.2014.04.001

  4. Inouye SK, Westendorp RG, Saczynski JS. Delirium in elderly peopleLancet. 2014;383(9920):911–922. doi:10.1016/S0140-6736(13)60688-1

  5. Banovic S, Zunic LJ, Sinanovic O. Communication Difficulties as a Result of DementiaMater Sociomed. 2018;30(3):221–224. doi:10.5455/msm.2018.30.221-224

  6. Green S, Reivonen S, Rutter LM, et al. Investigating speech and language impairments in delirium: A preliminary case-control studyPLoS One. 2018;13(11):e0207527. doi:10.1371/journal.pone.0207527

  7. Gold CA, Budson AE. Memory loss in Alzheimer's disease: implications for development of therapeuticsExpert Rev Neurother. 2008;8(12):1879–1891. doi:10.1586/14737175.8.12.1879

  8. O'Regan NA, Ryan DJ, Boland E, et al. Attention! A good bedside test for delirium?J Neurol Neurosurg Psychiatry. 2014;85(10):1122–1131. doi:10.1136/jnnp-2013-307053

  9. FDA-approved treatments for Alzheimer’s. Alzheimer's Association [internet].

  10. Biogen. Aduhelm (aducanumab-avwa) full prescribing information.

  11. Grover S, Avasthi A. Clinical Practice Guidelines for Management of Delirium in ElderlyIndian J Psychiatry. 2018;60(Suppl 3):S329–S340. doi:10.4103/0019-5545.224473

  12. Flanagan NM, Fick DM. Delirium superimposed on dementia. Assessment and interventionJ Gerontol Nurs. 2010;36(11):19–23.

  13. Morandi A, Davis D, Bellelli G, et al. The Diagnosis of Delirium Superimposed on Dementia: An Emerging ChallengeJ Am Med Dir Assoc. 2017;18(1):12–18. doi:10.1016/j.jamda.2016.07.014

Additional Reading
  • Flanagan NM, Fick DM. Delirium Superimposed on Dementia: Assessment and Intervention. Journal of Gerontological Nursing. 2010;36(11):19-23.
  • Journal of Gerontology: Medical Sciences. 2007, Vol. 62A, No. 11, 1306–1309. Delirium Superimposed on Dementia Predicts 12-Month Survival in Elderly Patients Discharged From a Postacute Rehabilitation Facility.
  • Lippmann S, Perugula ML. Delirium or dementia? 2016;13(9-10). ​https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5141598/

By Esther Heerema, MSW
Esther Heerema, MSW, shares practical tips gained from working with hundreds of people whose lives are touched by Alzheimer's disease and other kinds of dementia.