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Going into hospital: what is delirium, and can it be prevented?
Delirium is a sudden bout of confusion, often set off by an illness, an operation or a hospital stay. People with dementia are much more likely to get it, and it is linked to faster decline afterwards. In hospital patients generally, combined prevention programmes reduce it; whether they work as well for people who already have dementia has barely been tested.
How common it is
In a 2026 study of 2,556 older adults admitted to hospital, 37% had delirium. It became more common the more memory and thinking were impaired: 16% of people with no cognitive impairment, 59% of people with mild dementia and 77% of people with moderate or severe dementia. [1]
An earlier review found delirium in between 22% and 89% of people aged 65 and older with dementia, depending on where they were studied. [2]
Why it matters
In people with Alzheimer's followed by a Massachusetts research centre, memory test scores fell about twice as fast after an episode of delirium as before it: from 2.5 to 4.9 points a year. [3]
A 2010 review of older patients found that those who had delirium were more likely to have died at follow-up, and more likely to have moved into an institution: 33.4% against 10.7% of patients without delirium, after an average of 14.6 months. The links held after allowing for age, sex, other illness and existing dementia. [4]
These are associations. People who get delirium are often sicker to begin with, and none of these studies tested whether preventing delirium protects memory later. [4, 3]
What helps
A Cochrane review of 39 trials with 16,082 hospital patients outside intensive care found that multi-component programmes, which combine several preventive measures, reduced new cases of delirium compared with usual care (risk ratio 0.69; moderate-quality evidence). [5]
For people who already had dementia, the same review found one trial, with 50 participants, and its result was uncertain. [5]
Medicines did not show a clear benefit: the review found no clear evidence that antipsychotics as a group, the dementia drugs called cholinesterase inhibitors, or melatonin prevent delirium. One 400-person trial of the antipsychotic olanzapine did find fewer cases. [5]
Where people wait matters too. In a 2026 study of 11,105 older patients in an emergency department, people with dementia who spent a long time on a hallway bed were more likely to develop delirium or severe agitation; older patients without dementia were not. The authors say more research is needed before hospitals change how they assign rooms. [6]
What the research has not settled
How to prevent delirium in people who already have dementia is barely studied. A 2002 review found only one study that had looked for its causes and treatments in people with dementia, and the 2016 Cochrane review found one small trial. A 2025 practical review says delirium should be checked for whenever a person with dementia seems suddenly worse, or “different”. [2, 5, 7]
The studies this page draws on
- Frequent in dementia, deadliest without it: delirium and mortality in hospitalised older adults
- Delirium superimposed on dementia: a systematic review
- Delirium accelerates cognitive decline in Alzheimer disease
- Delirium in elderly patients and the risk of postdischarge mortality, institutionalization, and dementia: a meta-analysis
- Interventions for preventing delirium in hospitalised non-ICU patients
- Emergency Department Hallways Are Associated With Incident Delirium and Severe Agitation in Older Adults Living With Dementia
- Delirium superimposed on dementia (DSD)—a practical approach
More from the research library
472 of the library's 27,380 studies match; 288 have it in the title. Studies already listed above are not repeated. The 8 shown are the title matches first, then the highest-scoring.
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Processed electroencephalogram and evoked potential techniques for amelioration of postoperative delirium and cognitive dysfunction following non-cardiac and non-neurosurgical procedures in adults
We found moderate-quality evidence that postoperative cognitive dysfunction at three months could be reduced in these patients.
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Risk factors for incident delirium among older people in acute hospital medical units: a systematic review and meta-analysis
We aimed to synthesise data on risk factors for incident delirium and where possible conduct meta-analysis of these.
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Non-pharmacological interventions for preventing delirium in hospitalised non-ICU patients
There is moderate-certainty evidence regarding the benefit of multicomponent non-pharmacological interventions for the prevention of delirium in hospitalised adults, estimated to reduce incidence by 43% compared to usual care.
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A Focused Update to the Clinical Practice Guidelines for the Prevention and Management of Pain, Anxiety, Agitation/Sedation, Delirium, Immobility, and Sleep Disruption in Adult Patients in the ICU
The task force issued five statements related to the management of anxiety, agitation/sedation, delirium, immobility, and sleep disruption in adults admitted to the ICU.
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Preventing delirium: should non-pharmacological, multicomponent interventions be used? A systematic review and meta-analysis of the literature
A total of 21,788 citations were screened, and seven studies of diverse quality were included in the review, comprising 1,691 participants.
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Persistent delirium in older hospital patients: a systematic review of frequency and prognosis
We sought to determine the frequency and prognosis of persistent delirium (PerD) in older hospital patients by systematically reviewing original research on this topic.
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The risk factors for postoperative delirium in adult patients after hip fracture surgery: a systematic review and meta-analysis
Patients possessed above risk factors might be high-risk patients.
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Prevalence, Risk Factors, and Impact of Delirium on Hospitalized Older Adults With Dementia: A Systematic Review and Meta-Analysis
These findings suggested high prevalence and detrimental impact of DSD in hospitalized older adults, highlighting a need for early identification, prevention, and treatments.
How a study gets onto this list: its own title, summary, findings or note contains one of these terms — delirium, acute confusion. A study matched only in its text is shown with the sentence that matched, word for word. A score rates how much weight a study can bear, not whether its result is good news: how we score a study.