Coma is a state of prolonged loss of consciousness. It can have a variety of causes, including traumatic head injury, stroke, brain tumor, or drug or alcohol intoxication. A coma may even be caused by an underlying illness, such as diabetes or an infection.

Coma is a medical emergency. Quick action is needed to preserve life and brain function. Health care providers typically order a series of blood tests and a brain scan to try to learn what's causing the coma so that proper treatment can begin.

A coma doesn't usually last longer than several weeks. People who are unconscious for a longer time might transition to a lasting vegetative state, known as a persistent vegetative state, or brain death.


The symptoms of a coma commonly include:

  • Closed eyes.
  • Depressed brainstem reflexes, such as pupils not responding to light.
  • No responses of limbs except for reflex movements.
  • No response to painful stimuli except for reflex movements.
  • Irregular breathing.

When to see a doctor

A coma is a medical emergency. Seek immediate medical care for the person in a coma.


Many types of problems can cause a coma. Some examples are:

  • Traumatic brain injuries. These are often caused by traffic collisions or acts of violence.
  • Stroke. Reduced or stopped blood supply to the brain, known as a stroke, can result from blocked arteries or a burst blood vessel.
  • Tumors. Tumors in the brain or brainstem can cause a coma.
  • Diabetes. Blood sugar levels that become too high or too low can cause a coma.
  • Lack of oxygen. People who have been rescued from drowning or revived after a heart attack might not awaken due to lack of oxygen to the brain.
  • Infections. Infections such as encephalitis and meningitis cause swelling of the brain, spinal cord or the tissues that surround the brain. Severe cases of these infections can result in brain damage or a coma.
  • Seizures. Ongoing seizures can lead to a coma.
  • Toxins. Exposure to toxins, such as carbon monoxide or lead, can cause brain damage and a coma.
  • Drugs and alcohol. Overdosing on drugs or alcohol can result in a coma.


Although many people gradually recover from a coma, others enter a persistent vegetative state or die. Some people who recover from a coma end up with major or minor disabilities.

During a coma, bedsores, urinary tract infections, blood clots in the legs and other problems may develop.

Dec. 14, 2022
  1. Overview of coma and impaired consciousness. Merck Manual Professional Edition. http://www.merckmanuals.com/professional/neurologic-disorders/coma-and-impaired-consciousness/overview-of-coma-and-impaired-consciousness. Accessed Nov. 8, 2020.
  2. Daroff RB, et al. Stupor and coma. Bradley's Neurology in Clinical Practice. 7th ed. Elsevier; 2016. https://www.clinicalkey.com. Accessed Nov. 6, 2020.
  3. Young GB. Stupor and coma in adults. http://www.uptodate.com/contents/search. Accessed Nov. 6, 2020.
  4. Coma information page. National Institute of Neurological Disorders and Stroke. https://www.ninds.nih.gov/Disorders/All-Disorders/Coma-Information-Page. Accessed Nov. 6, 2020.


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