by EBSCO Medical Review Board


A coma is a state of deep unconsciousness. A person in a coma cannot react to events in the environment.

A coma needs emergency treatment right away.


Information about the environment is normally passed from the brainstem to the rest of the brain. This feedback allows a person to be aware of and react to the environment. A coma is caused by a breakdown in this system.

Brainstem and Cerebrum
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This may happen due to:

  • Severe head injury, such as from car accidents, violence, or falls
  • Brain illness such as:
  • Lack of oxygen to the brain because of:
  • Severe general illness such as:
    • Infections
    • Liver or kidney failure
    • High carbon dioxide levels
    • Carbon monoxide poisoning
    • Toxicity from poisons, medicines, alcohol , or drugs
    • Abnormal hormone levels, such as from the thyroid or adrenal gland
    • Abnormal blood chemistries, such as sodium or calcium
    • Very low or very high levels of blood glucose
    • Very low or very high body temperatures
    • Poor nutrition
    • Inherited metabolic diseases

Risk Factors

Things that may raise the risk of coma are:

  • Severe illness
  • Diabetes
  • Liver, kidney, or heart disease
  • A history of blood clots
  • Exposure to poisons, such as carbon dioxide
  • Cancer and chemotherapy


Symptoms of a coma are:

  • Not reacting to:
    • Pain
    • Sound
    • Touch
    • Sight
  • Moving the body without control, such as:
    • Jerking
    • Shaking
    • Trembling
    • Eyes opening and closing
    • Irregular breathing


The doctor will gather information from friends, family members, or people who were there when symptoms started. The doctor will ask about the person's symptoms and health history, including any use of drugs or alcohol. A physical exam will be done. It will include tests of the nervous system.

Blood and urine tests will be done. The fluid around the brain and spine will also be tested. This can be done with a lumbar puncture.

Images may be taken. This can be done with:

Brain activity may be tested. This can be done with:


A coma is a medical emergency. Doctors will work quickly to find and treat the cause.

Supportive care will be needed, such as:

Ongoing care will be needed for a person who has a coma that does not resolve.


The risk of this problem may be lowered by taking steps to avoid head injury, such as:

  • Wearing a seatbelt in motor vehicles
  • Using safe, age-based sports methods for children
  • Wearing a helmet when:
    • Playing a contact sport like football, soccer, or hockey
    • Riding a bike or motorcycle
    • Using skates, scooters, and skateboards
    • Catching, batting, or running bases in baseball or softball
    • Riding a horse
    • Skiing or snowboarding


Brain Injury Association of America 

National Institute of Neurological Disorders and Stroke 


Brain Injury Association of Canada 

Ontario Brain Injury Association 


Coma. EBSCO DynaMed website. Available at: Accessed January 25, 2021.

Edlow JA, Rabinstein A, et al. Diagnosis of reversible causes of coma. Lancet. 2014 Dec 6;384(9959):2064-2076.

Revision Information

  • Reviewer: EBSCO Medical Review Board Rimas Lukas, MD
  • Review Date: 12/2020
  • Update Date: 01/25/2021