A coma can result from complications of conditions such as diabetes or an infection, or from a traumatic incident involving a blow to the head or a lack of oxygen. Doctors sometime induce a coma to protect a person from pain and complications during the healing process.

A coma is state of deep unconsciousness. It is similar to a deep sleep, but the person cannot wake up or respond in the usual way to their environment. Their levels of consciousness and responsiveness will depend on how much the brain functions.

A coma can last from a few days to a few weeks. The outcome will depend on the cause and any brain damage that has occurred.

If a person enters a coma following a medical or traumatic event, it is a medical emergency. Doctors may need to take rapid action to preserve their life and brain function.

This article explains what a coma is, the possible causes, and how to recognize the signs. It also explores what happens during a coma, the potential complications, and how doctors sometimes use it as a treatment.

Fast facts on coma

  • During a coma, a person does not react to external stimuli, and they will not show normal reflex responses.
  • People in a coma do not have sleep-wake cycles.
  • Reasons for a coma include drug or alcohol intoxication, central nervous system disease, infections, and a stroke.
  • Depending on the cause and the extent of damage, a coma can occur rapidly or gradually, and it can last from several days to months, though most last from days to weeks.
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A coma is a deep state of unconsciousness. The outcome of a coma depends on the cause and severity of the damage a person has sustained or the diagnosed condition.

Sometimes, a doctor will induce a coma using medications. For example, they might do this to protect the person from intense pain during a healing process or to preserve higher brain function following a form of brain trauma.

However, in severe cases, a person’s condition may not change after an extended period. Doctors may reclassify them as being in a persistent vegetative state. If this state lasts for months, a person may be unlikely to wake up.

Recognizing the signs of a coma

A first responder may start by using the alert, verbally and painfully responsive, and unresponsive (AVPU) scale to gauge the level of consciousness.

The AVPU scale looks at the following areas:

  • Alertness: How alert is the person?
  • Vocal stimuli: Do they respond to another person’s voice?
  • Painful stimuli: Do they respond to pain?
  • Consciousness: Are they conscious?

Alert is the most conscious state, and unconscious is the least. This scale helps a healthcare professional assess whether this is likely an emergency. If the person is alert, there is no risk of coma.

Anyone with the person should try to remember what occurred just before the signs of a coma started. This information will help doctors determine the underlying cause and give them a better idea of what treatment to use.

People in a state of deep unconsciousness may be at risk of asphyxiation. They may need medical help to secure the airways and ensure continued breathing. This may involve a tube that passes through the nose or mouth into the lungs.

As a person in a coma cannot communicate, the diagnosis relies on outward signs. These include:

  • closed eyes
  • limbs that do not respond or voluntarily move, except for reflex movements
  • lack of response to painful stimuli, except for reflex movements

How long these signs take to develop and their duration will depend on the underlying cause.

Before entering a coma, a person with worsening low blood sugar, known as diabetic shock, or excessively high levels of carbon dioxide in the blood, called hypercapnia, may first experience headaches, irritability, and slurred speech.

Without treatment, their ability to think clearly will gradually decrease, potentially resulting in the loss of consciousness.

If a coma results from a severe injury to the brain or a subarachnoid hemorrhage, the symptoms may appear suddenly.

How it affects people

The National Institute of Neurological Disorders and Stroke (NINDS) suggests that people in a coma do not react to their surrounding environment due to the suppression of their thinking abilities.

However, automatic functions, such as breathing and circulation, usually continue to function. The NINDS suggests that spontaneous movements, such as a grimace, laugh, or cry, may also occur as a reflex.

A person in a coma cannot respond or make voluntary actions to pain, light, or sound in the usual way.

However, according to research from 2019, a person in a coma may be able to hear sounds in their environment. Examples include the footsteps of someone approaching or the voice of a person speaking.

A 2015 study found evidence that the voices of family members and loved ones could help improve responsiveness in people during a coma. While some of the participants underwent either familiar auditory sensory training (FAST), those in the placebo group received only silence. MRI scans showed neurological improvements in those who experienced FAST.

The causes of a coma vary, but they all involve some level of injury to the brain or central nervous system (CNS). They include:

  • Diabetes: The blood sugar levels of a person with diabetes can sometimes rise too much or fall too low, known as hyperglycemia and hypoglycemia, respectively. If either of these states continues for too long, a coma can result.
  • Hypoxia, or lack of oxygen: A coma can occur if the supply of oxygen to the brain becomes reduced or cut off — for example, during a heart attack, stroke, or near-drowning incident.
  • Infections: Severe inflammation of part of the CNS or the tissues surrounding the brain — known as encephalitis and meningitis, respectively — can result in a coma.
  • Toxins and drug overdose: Exposure to carbon monoxide can result in brain damage and coma, as can some drug overdoses.
  • Traumatic brain injuries: Road traffic accidents, sports injuries, and violent attacks that involve a blow to the head can cause coma.

Doctors use the GCS to assess the severity of impaired consciousness in people with all types of acute medical conditions and trauma.

This scale gives individuals a score according to their verbal and physical responses and how easily they can open their eyes.


The range of scores is 1–4, where:

  • 1: The person does not open their eyes.
  • 2: Pain causes the eyes to open.
  • 3: The eyes open in response to a voice.
  • 4: The person can open their eyes spontaneously.


The range of scores is 1–5, where:

  • 1: There is no sound.
  • 2: The person can mumble, but it is impossible to understand them.
  • 3: The person utters inappropriate words.
  • 4: The person can speak, but they are confused.
  • 5: Communication is normal.

Motor, or physical, reflexes

The range of scores is 1–6, with 1–5 describing a person’s response to pain.

  • 1: The person makes no movement.
  • 2: A limb straightens in response to pain
  • 3: The reaction to pain is unusual.
  • 4: The person moves away from pain.
  • 5: They can pinpoint the site of the pain.
  • 6: The person can obey commands.

An overall score of 8 or less indicates a coma. The condition is moderate if the overall score is 9–12. If the overall score is 13 or more, the impairment to consciousness is minor.

The possible complications of a coma relate to the following:

Doctors pay close attention to a person’s condition to prevent any secondary brain injury. This may require respiratory and cardiovascular support.

A medical history alongside various tests can help determine the cause of a coma, which informs the treatment decisions.

Medical history

Doctors may ask friends, family, police, and witnesses, if appropriate, the following:

  • whether the coma or the preceding symptoms started slowly or suddenly
  • if the person had or appeared to have any vision problems, dizziness, stupor, or numbness before the coma
  • whether the person has diabetes, a history of seizures or stroke, or any other condition
  • what medications or other substances the person may have taken

Physical tests

The aim of these tests is to trigger varying reflexive eye movements. The type of response varies depending on the cause of the coma.

Tests previously involved squirting very cold or warm water into the ear canals, which doctors refer to as caloric testing.

Nowadays, doctors are more likely to make a diagnosis based on the following evaluations:

  • Extraocular movements: Do the eyeballs move up, down, and side to side?
  • Pupillary: Do the pupils change in size in response to light?
  • Corneal: Does the person blink when a medical professional touches the eyeball with a wisp of cotton?
  • Cough: Does this occur when oral secretions are present?
  • Gag reflex: Does a doctor touching the back of the mouth trigger this reflex?

Blood tests

Doctors will likely use blood tests to check:

Lumbar puncture

Doctors also refer to this procedure as a cerebral spinal fluid (CSF) analysis. It involves a doctor inserting a needle into the person’s spinal canal to measure the pressure of the CSF and extract some to test for infections or disorders of the CNS.

Imaging scans of the brain

These scans will help determine whether and where there is any brain injury or damage.

A CT scan or an MRI scan will reveal blockages or other abnormalities. An electroencephalogram will measure the electrical activity within the brain.

A coma is usually a serious medical emergency. Healthcare professionals will start by ensuring the immediate survival of the individual. They will secure their breathing and circulation to maximize the amount of oxygen that reaches the brain.

As a 2021 review explains, further treatment will then depend on the underlying cause of the coma.

The treatment options may include administering:

  • glucose, even before the results of blood tests are available, in case the person is in diabetic shock or has a brain infection
  • a drug called naloxone (Narcan), if severe intoxication has likely caused the coma
  • vitamin B1, if the person has alcohol use disorder, which can lead to a deficiency of this vitamin

In all cases, doctors should also aim to keep the individual’s blood pressure at a good level and maintain their breathing by protecting their airways.

In some cases, doctors may need to relieve pressure within the individual’s skull by draining the excess CSF or prescribing medication that reduces brain swelling, such as mannitol and hypertonic saline.

If doctors can successfully treat the cause of the coma, the person may eventually awaken with no permanent damage. They may experience confusion initially, but they will usually remember what happened before the coma and can carry on with their life. Typically, some rehabilitation or physical therapy is necessary.

If brain damage has occurred, a long-term impairment may result. If the person awakens, they may need to relearn basic skills, and they may not remember what happened. However, with support, such as physical and occupational therapy, many people can improve their quality of life.

Due to the grading scales for symptoms and the range of diagnostic tests available, doctors can usually detect what a person’s condition means and determine the best approach to treatment.