Alasdair MacLullich

Delirium: a sudden change that needs attention

Delirium is a sudden change in attention, thinking and awareness. It develops over hours or days and often fluctuates. A new change needs medical assessment because delirium usually accompanies an acute illness, injury, medication effect, or a combination of causes.

Get help with sudden confusion Find the right information

If this is happening now

New sudden confusion needs medical assessment now. Contact the urgent or emergency medical service where the person is. If the person is hard to wake, has trouble breathing, shows signs of a stroke, has a seizure or head injury, or is getting worse quickly, call the local emergency number immediately (999 in the UK).

Delirium Support explains what to do and what to tell the clinical team. It gives general information, not advice about an individual.

Five points for practice

  1. The change is acute and often fluctuates

    Delirium develops quickly. A person may be more confused at some times of day and clearer at others. This pattern differs from the usual slow development of most dementias, although delirium and dementia often occur together.

  2. Delirium can be quiet

    Some people become agitated or distressed. Others become unusually sleepy, withdrawn, or less responsive. The quieter form is easy to miss.

  3. The cause or causes need attention

    Clinicians look for illness, medication effects, pain, dehydration, recent surgery and other possible causes. More than one factor may be present.

  4. Knowing the person's usual state helps

    Relatives and carers can often say precisely what changed and when. That information helps clinicians judge whether the person's attention, alertness, or thinking differs from normal.

  5. Recovery can take time

    Some people improve quickly when the causes are treated. For others, recovery is slower and uneven. Follow-up is needed when thinking, function, sleep, or distress remain changed.

These points are consistent with NICE guideline CG103, SIGN guideline 157, and the review by Wilson and colleagues.

My work on delirium

My clinical and research work centres on the recognition, assessment and care of people with delirium. I originally designed the 4AT with Tracy Ryan and Helen Cash in 2011, and remain responsible for its updates.

The 4AT gives clinicians a brief way to assess possible delirium and cognitive impairment. The first validation study included 234 hospitalised older people. The official 4AT website provides the evidence, translations and practical guidance.

The links below cover research, education, public information and scientific publishing.

The 4AT in use

NICE recommends the 4AT for assessment when indicators of delirium are identified in hospital or long-term care, except in critical care or the recovery room after surgery. SIGN recommends it to identify probable delirium in emergency and acute hospital settings. It is free to use, needs no registration and is available in more than 20 languages.

Use the official 4AT, work through clinical cases, or read the free practical manual. The research page gives study findings and links to the published evidence.

Choose the route that fits

Each site has a distinct audience and purpose. For patients and families, a good place to start is What is delirium? on Delirium Support.

  • Patients, families and carers

    Understand what is happening

    Plain English information about signs, urgent help, delirium and dementia, supporting someone, and recovery.

    Visit Delirium Support

  • Clinicians

    Use the 4AT

    The assessment, scoring guidance, evidence, translations, frequently asked questions and case examples.

    Visit the 4AT

  • Clinicians and researchers

    Compare assessment tools

    A referenced catalogue of delirium instruments, including their purpose, evidence, limitations and source access.

    Visit Delirium Tools

  • Students and health professionals

    Learn about delirium

    Structured online education about recognition, assessment and care.

    Visit Delirium Academy

  • Clinicians, researchers and policymakers

    Read analysis and commentary

    Longer articles about delirium care, science, measurement and policy.

    Visit Delirium Words

  • Journalists and organisers

    Request comment or a talk

    Current roles, areas of expertise, approved biographies and the institutional contact route.

    Media information

Evidence and guidance

Page reviewed 13 September 2026. Source links last checked 4 September 2026.

Delirium information