Behavior - unusual or strange

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Central nervous system

Unusual or strange behavior involves performing actions that are not normal for the person.

Acting strangely

Unusual or strange behavior may include:

• Loss of memory that continues over time or gets worse
• Loss of the ability to concentrate and perform other mental tasks

There are many causes of unusual or strange behavior, including medical and psychiatric illnesses. Two of the more common medical causes are:

• Delirium -- Sudden or quick onset of reduced consciousness, awareness, perception, or thought that may be a symptom of a medical illness such as brain or mental dysfunction
• Dementia -- Chronic, worsening loss of cognitive function that occurs with brain disorders

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Psychiatric illnesses that are often associated with unusual or strange behavior include:

• Anxiety disorder
• Bipolar disorder
• Depression
• Psychosis
• Schizophrenia

Possible causes of strange behavior in older people include:

• Alcohol consumption in excess
• Alzheimer's disease
• Chronic exposure to cold (hypothermia)
• Dehydration
• Hypoglycemia
• Electrolyte abnormality
• Emotional problems (depression or feeling useless)
• Head injury (subdural hematoma)
• Heart attack, pulmonary embolism, stroke
• Infection (including pneumonia, gastroenteritis, urinary tract infection)
• Malnutrition (particularly vitamin B12 and thiamine deficiency)
• Medications (sleeping pills, pain relievers)
• Thyroid disorders (either underactive or overactive)
• Unfamiliar surroundings

Possible causes in people of all ages include:

• Diseases affecting the nervous system (neurological diseases)
• Recreational drugs (such as amphetamines and cocaine)
• Environmental hazards
• Low or high thyroid function
• Non-neurological diseases, especially those with fever (for example, pneumonia)
• Side effects of medications

Review Date: 02/06/2010
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Luc Jasmin, MD, PhD, Department of Neurosurgery at Cedars-Sinai Medical Center, Los Angeles, and Department of Anatomy at UCSF, San Francisco, CA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).