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


Information about your environment is normally passed from the brainstem into 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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The system may be interrupted by:

  • Severe head injury—most often a result of car accidents, violence, or falls.
  • Brain illness such as:
  • Lack of oxygen to the brain which may be due to:
  • Severe general illness such as:
    • Severe bodily infections
    • Severe acute liver or kidney failure
    • High carbon dioxide levels
    • Carbon monoxide poisoning
    • Toxicity from poisons, medication, 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 sugar
    • Very low or very high body temperatures
    • Severe nutrient deficiency
    • Liver failure
    • Kidney failure
    • Inherited metabolic diseases

Risk Factors

Factors that may increase your chance of a coma include:

  • Severe illness
  • Diabetes
  • Liver, kidney, or cardiovascular disease
  • Tendency to have blood clots
  • Exposure to poisonous substances, such as carbon dioxide
  • Cancer and chemotherapy

Brain injury is more common in men. Age groups that are more likely to experience brain injury include 5 years or younger, 15-24 years old, and 75 years or older. Risk factors for brain injury include:

  • Traveling in a vehicle at a high rate of speed or at night
  • Lack of sleep
  • A previous head injury


Symptoms of a coma include the following:

  • No response to stimulus, such as:
    • Pain
    • Sound
    • Touch
    • Sight
  • Spontaneous body movements, such as:
    • Jerking
    • Shaking
    • Trembling
    • Eyes opening and closing
    • Irregular breathing


Since the patient cannot speak, information will need to be gathered from other sources, including friends, family members, and people who witnessed an accident if one occurred. This is important to help with diagnosis. The doctor will also need to know about the person’s medical history and any drug or alcohol use. It is important to provide honest information in order to help with treatment.

The doctor will test reflexes, listen to breathing, and examine the eyes. A physical exam will also be done, including tests of the nervous system.

The patient's bodily fluids will be tested. This can be done with:

Images may be taken of the patient's bodily structures. This can be done with:

The patient's brain activity may be tested. This can be done with:

Clinical findings of comatose patients can be rated according to the Glasgow Coma Scale (GCS). This scale assesses 3 different functions: eye opening, motor response, and verbal response. Scores can range from 15 to 3. A lower score indicates less responsiveness. Scores are interpreted as follows:

  • 15-13—mild brain injury
  • 12-9—moderate brain injury
  • 8 or less—a severe brain injury


A coma is a medical emergency. Any unconscious person should be taken to the emergency room right away.

Emergency Treatment

Doctors will work quickly to determine the cause of the coma. Further treatment will depend on the cause of the coma. Supportive care may include:

  • Monitoring of vital signs
  • Oxygen therapy
  • Delivering fluids directly into the blood through an IV
  • Mechanical ventilation to help support breathing

If a specific cause of the coma is suspected, supportive care may also include:

  • Glucose delivered through IV—in case low blood sugar is causing the coma
  • Naloxone—if a narcotics overdose is suspected
  • Thiamine (vitamin B1) may be given with glucose if alcohol use disorder or malnutrition is suspected

In some cases, surgery may correct the cause of a coma.

Ongoing Treatment

If the coma persists after emergency care, ongoing care may be needed. After the person is stabilized, treatment will focus on providing nutrition and preventing infections. The care staff will also work to prevent pressure sores.


To help reduce your chance of a coma:

  • Wear a seatbelt. Make sure infants and small children are securely fastened in a child safety seat.
  • Children aged 12 years and under should ride in the back seat of a vehicle.
  • Wear an appropriate helmet while biking, rollerblading, playing contact sports, skiing, snowboarding, and riding a motorcycle.
  • Wear athletic mouth guards while playing sports.
  • Do not abuse alcohol or drugs.
  • If you have diabetes, see your doctor regularly and take appropriate steps to regulate your blood sugar levels.
  • If you are ill or take medication, see your doctor regularly for check-ups.

Brain Injury Association of America

National Institute of Neurological Disorders and Stroke


Brain Injury Association of Canada

Ontario Brain Injury Association


Coma. EBSCO DynaMed Plus website. Available at: Updated August 22, 2017. Accessed November 8, 2017.

Last reviewed November 2018 by EBSCO Medical Review Board Rimas Lukas, MD  Last Updated: 3/21/2017