Coma

Learn what can cause this state of prolonged loss of consciousness. While a coma rarely lasts longer than a few weeks, some people never wake from one.

Update Date: 03.06.2026

Overview
Symptoms
Causes
Risk factors
Complications
Diagnosis
Treatment
Preparing for an appointment

Overview

Coma is a state of prolonged loss of consciousness. People in this state are not aware of their surroundings. Coma can have a variety of causes, including traumatic head injury, stroke, brain tumor, or drug or alcohol intoxication. It may even be caused by an underlying illness, such as diabetes or an infection.

Because coma is a medical emergency, quick action is needed to preserve life and brain function. Healthcare professionals 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 state of unresponsive wakefulness, previously known as a persistent vegetative state. Some people may ultimately experience brain death.

Symptoms

The symptoms of a coma commonly include:

  • Closed eyes.
  • Depressed brainstem reflexes, such as pupils not responding to light.
  • No responses of the arms or legs 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 a person who is not conscious.

Causes

A coma can be caused by a variety of factors. Some examples are:

  • Traumatic brain injuries. These are often caused by auto crashes or acts of violence.
  • Stroke. Less 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 coma.
  • Diabetes. Blood sugar levels that become too high or too low can cause 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. Serious infections can result in brain damage or coma.
  • Seizures. Ongoing seizures can lead to coma.
  • Toxins. Exposure to toxins, such as carbon monoxide or lead, can cause brain damage and coma.
  • Drugs and alcohol. Overdosing on legal or illegal drugs or alcohol can result in coma.

Risk factors

Risk factors for coma include:

  • Serious head injury.
  • Stroke.
  • Bleeding in and around the brain, known as an intracranial bleed.
  • Brain tumor.
  • Serious infection, such as sepsis, encephalitis or meningitis.
  • Near drowning, which decreases oxygen to the brain.
  • Excessive use of alcohol or use of illegal drugs.
  • Exposure to carbon monoxide, lead or other toxins.

Conditions that increase the risk of a coma include:

  • Diabetes with blood sugar that's very high or very low.
  • Serious hypothyroidism, also called underactive thyroid.
  • Very low sodium in the blood.
  • Heart failure, which can cause very low blood pressure.
  • Epilepsy, including having seizures that last more than five minutes or that happen one after another without the person regaining consciousness.

The risk of coma goes up with age. This is especially true if older adults have a brain disease or another condition such as diabetes, high blood pressure or kidney disease. Older adults are also at risk of a coma if they take several medicines, which can lead to interactions or accidental overdose.

Complications

Many people gradually recover from a coma, but some may have complications that include major or minor disabilities. Others may enter a state of unresponsive wakefulness syndrome, previously known as a persistent vegetative state. Some people experience brain death and die.

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

Diagnosis

To diagnose coma, healthcare professionals rely on physical clues and information provided by families and friends. Helpful information includes:

  • Events leading up to the coma, such as vomiting or headaches.
  • Details about how the person lost consciousness, including whether it occurred quickly or over time.
  • 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, also called a transient ischemic attack.
  • Recent changes in the person's health or behavior.
  • Medicine and drug use, including prescription medicines, medicines taken without a prescription, and legal and illegal drugs.

Physical exam

The exam is likely to include:

  • Checking the 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 figure out 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, also known as 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 this test, a healthcare professional 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 find 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. This test can help find if seizures might be the cause of a coma.

Treatment

Coma requires emergency treatment. Healthcare professionals typically first check the airway and help support breathing and circulation. Treatment might include breathing help, 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 a medicine or drug overdose, healthcare professionals 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 person regains function. Recovery usually occurs gradually. A person with serious brain damage might have permanent disabilities or never regain consciousness.

Preparing for an appointment

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

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 person before the coma. You might be asked the following questions:

  • Did the coma start suddenly, or did it happen more gradually?
  • Were there problems with vision, dizziness or weakness beforehand?
  • Does the person have a history of diabetes, seizures or strokes?
  • Did the 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 person's ability to function before the coma, such as falls or confusion?
  • Did the person use prescription medicines, medicines you can buy without a prescription, or legal or illegal drugs?

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