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Delirium, also referred to as "acute confusional state" or "acute brain syndrome," is a condition of severe confusion and rapid changes in brain function. Shorter in duration than dementia, it comprises a cluster of symptoms that may result from a treatable physical or mental illness. Delirium can also be a side effect of some medications.


The DSM-5 diagnostic criteria for delirium include:

  • A disturbance in attention and awareness, which:
    • develops in a short time period (usually over the course of hours or a few days)
    • represents a change from typical levels of attention and awareness
    • tends to fluctuate in severity of the course of a day
  • An additional disturbance in cognition (such as in memory, language, perception, or orientation to time or place)

For a diagnosis of delirium, such disturbances must not be better explained by a different neurocognitive disorder or occur during a low-arousal state such as a coma. Further, there must be evidence that the symptoms are the direct result of another medical condition, substance intoxication or withdrawal, exposure to a toxin, or multiple causes.

Delirium may coincide with a disturbance in the sleep-wake cycle (including, for example, sleepiness during the day and wakefulness at night) as well as in a person's emotional state, which may shift unpredictably. Patients with delirium can switch quickly between hyperactive and hypoactive states.

Prevalence is highest among hospitalized older individuals, affecting an estimated 14 percent of individuals over the age of 85.

Delirium often lasts about one week in a hospital setting, but symptoms may persist for longer. Delirium can progress to coma or death, especially if the underlying cause is not treated.

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Delirium is usually the temporary result of a physical or mental illness. It can be caused by disorders that deprive the brain of oxygen or other substances or that result in the accumulation of toxins in the brain. Drug use, overdose, or withdrawal; infections, such as urinary tract infections; poisons; severe sleep deficits; and general anesthesia are among the varied causes of delirium.


Treatment varies depending on the specific condition causing delirium, and may require hospitalization.

Medications that worsen confusion—such as alcohol and illegal drugs, anticholinergics, analgesics, and central nervous system depressants, or others—may be stopped or changed. Medications or behavioral interventions may be used during treatment to control hazardous behaviors.

Tools for increasing orientation to one's surroundings and the use of eyeglasses and hearing aids may also be helpful for individuals with delirium.

Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition
National Institutes of Health
Last updated: 02/22/2019