Delirium (also known as encephalopathy) is an acute confusional state that presents as fluctuations in level of alertness, inattention, or altered level of consciousness and disorganized thinking. Delirium develops subacutely over hours to days and can persist for days to weeks. Patients with underlying cognitive deficits, older individuals, and those with functional disabilities are at higher risk for developing delirium given decreased cognitive reserve.

Etiologies of delirium are broad and include systemic toxic, metabolic, nutritional, infectious, or pharmacologic causes as well as acute brain disorders (eg, stroke, seizures). Delirium is classically thought to be transient, although not all patients return to their baseline. Delirium can be hyperactive, with psychomotor agitation and emotional disturbances, or hypoactive.

See Drug Reaction Data table for a list of potential pharmacologic causes. Related topic: Drug-induced psychosis.