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.


Because people in a coma can't express themselves, health care providers must rely on physical clues and information provided by families and friends. Be prepared to provide information about the affected person, including:

  • Events leading up to the coma such as vomiting or headaches.
  • Details about how the affected person lost consciousness, including whether it occurred quickly or over time.
  • Noticeable symptoms before losing consciousness.
  • Medical history, including other conditions the person may have had in the past. This includes whether the person has had a stroke or ministroke.
  • Recent changes in the person's health or behavior.
  • The person's drug use, including prescription and nonprescription medicines, unapproved medicines, and illicit drugs.

Physical exam

The exam is likely to include:

  • Checking the affected person's movements and reflexes, response to painful stimuli, and pupil size.
  • Observing breathing patterns to help diagnose the cause of the coma.
  • Checking the skin for signs of bruises due to trauma.
  • Speaking loudly or pressing on the angle of the jaw or nail bed while watching for signs of arousal, such as vocal noises, eyes opening or movement.
  • Testing reflexive eye movements to help determine the cause of the coma and the location of brain damage.
  • Squirting cold or warm water into the affected person's ear canals and watching eye reactions.

Laboratory tests

Blood samples typically are taken to check for:

  • Complete blood count.
  • Electrolytes and sugar. Sugar is also called glucose.
  • Thyroid, kidney and liver functions.
  • Carbon monoxide poisoning.
  • Drug or alcohol overdose.

A spinal tap, also known as a lumbar puncture, can check for signs of infections in the nervous system. During a spinal tap, a health care provider inserts a needle into the spinal canal and collects a small amount of fluid for analysis.

Brain scans

Imaging tests help pinpoint areas of brain injury. Tests might include:

  • CT scan. This uses a series of X-rays to create a detailed image of the brain. A CT scan can show bleeding in the brain, tumors, strokes and other conditions. This test is often used to diagnose and determine the cause of a coma.
  • MRI. This uses powerful radio waves and a magnetic field to create a detailed view of the brain. An MRI scan can detect bleeding in the brain, brain tissue damaged by an ischemic stroke and other conditions. MRI scans are particularly useful for examining the brainstem and deep brain structures.
  • Electroencephalogram (EEG). This measures the electrical activity inside the brain through small metal discs called electrodes attached to the scalp. A low electrical current travels through the electrodes, which record the brain's electrical impulses. This test can determine if seizures might be the cause of a coma.


A coma is a medical emergency. Health care providers typically first check the affected person's airway and help maintain breathing and circulation. Providers might give breathing assistance, medicines through a vein and other supportive care.

Treatment depends on the cause of the coma. A procedure or medicines to relieve pressure on the brain due to brain swelling might be needed. Emergency responders might give glucose or antibiotics through a vein in the arm. These may be given even before blood test results return in cases of very low blood sugar or an infection affecting the brain.

If the coma is the result of drug overdose, health care providers typically give medicines to treat the condition. If the coma is due to seizures, medicines can control seizures. Other treatments might focus on medicines or therapies to address an underlying disease, such as diabetes or liver disease.

Sometimes the cause of a coma can be completely reversed, and the affected person regains function. Recovery usually occurs gradually. A person with severe brain damage might have permanent disabilities or never regain consciousness.

Preparing for an appointment

A coma is an emergency medical condition. If you are with a person who develops symptoms of a coma, call 911 or emergency medical help immediately.

When you arrive at the hospital, emergency room staff will need as much information as possible from family and friends about what happened to the affected person before the coma. You might be asked the following questions while riding in the ambulance:

  • Did the coma start abruptly or gradually?
  • Were there problems with vision, dizziness or weakness beforehand?
  • Does the affected person have a history of diabetes, seizures or strokes?
  • Did the affected person talk about changes in health in the time leading up to the coma, such as a fever or worsening headache?
  • Did you notice changes in the affected person's ability to function in the time leading up to the coma, such as frequent falls or confusion?
  • Did the affected person use prescription or nonprescription drugs?

Content From Mayo Clinic Updated: 12/13/2022
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