What Is a Coma? Symptoms, Causes, Diagnosis and Treatment
Updated: 3 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick Answer: What is a coma?
A coma is a medical emergency caused by anything that disrupts how the brain stays awake, including head injury, oxygen loss, stroke, infections, blood sugar problems, overdose and seizures [3] [5]. Treatment keeps the person safe with breathing and IV support, handles immediate emergencies and treats the root cause. Most comas end within a few weeks, with waking or another reduced-consciousness state.
Key takeaways
Key point | What it means |
A coma is an emergency | Call emergency services immediately, because delayed treatment can be life-threatening |
It is deeper than sleep | |
It is usually short-lived | A coma rarely lasts more than 2 to 4 weeks [6] |
The cause drives the outcome | Head injury, oxygen loss, stroke, infection, overdose and diabetes all lead to different paths |
Speaking may help | Awareness is hard to judge from outside, so families are encouraged to keep talking |
What the research says
The Glasgow Coma Scale has been the bedside standard for more than 40 years, but it is not a crystal ball. A Lancet Neurology review marking the scale's 40th anniversary (in use since 1974) concluded that individual patients are best described by the scale's three components, while the total score is best used to describe groups, and that predictions should only be made together with other variables (Teasdale et al., Lancet Neurol, 2014 [2]).
Stroke, infection and metabolic problems were the leading causes of non-traumatic coma in one large hospital series. In a three-year study of 408 adults with non-traumatic coma at a tertiary hospital in Cameroon, stroke caused 29.6% of cases, infections 19.8% and metabolic disorders 12.6%, and the cause stayed unknown in 23.3%. In-hospital mortality was 66.4%, and a Glasgow Coma Scale score below 6 was one of the predictors of death. This was a single-centre retrospective study in a resource-limited setting, so mortality may differ elsewhere (Gams Massi et al., Afr J Emerg Med, 2024 [3]).
For comas that become prolonged, the American Academy of Neurology says outlook depends on the cause and the state the person is in. Its 2018 guideline advises counselling families that, in adults, a minimally conscious state (compared with a vegetative state) and a traumatic cause (compared with a non-traumatic one) are linked with more favourable outcomes, that prognosis is not universally poor, and that the Coma Recovery Scale-Revised can help with prognosis (Level B) (Giacino et al., Neurology, 2018 [1]).
What Is a Coma?
A coma is a deep state of unconsciousness [5] [6]. A person in a coma cannot wake up, think, talk, respond to conversation or react to pain, no matter how loud or strong the stimulus is. They are unaware of what is happening around them, which is why a coma is always treated as a medical emergency.
Two parts of the brain keep you awake and aware: the reticular activating system in the brainstem, a network of nerve cells that maintains wakefulness, and the cerebral hemispheres, the two largest areas of the brain that handle thinking. A coma occurs when something disrupts one or both of these systems.
A coma is not a diagnosis in itself. It is a state that results from an underlying problem, and that problem determines the type of coma, the treatment and the likely outcome.
Type of coma | What causes it |
Anoxic brain injury | Lack of oxygen or blood flow to the brain, such as after cardiac arrest or drowning |
Diabetes-related | Very low or very high blood sugar levels |
Medically induced | A controlled coma created in a medical setting to let the brain rest and heal |
Toxic-metabolic encephalopathy | Too much or too little of certain chemicals in the body, such as in a drug overdose |
Trauma-induced | A serious head injury |
Signs and Symptoms of a Coma
The hallmark of a coma is that the person cannot be woken up. Signs vary from person to person, and their severity depends on the depth of the coma.
Sign | What it looks like |
Closed eyes | The eyes remain shut and the person cannot be roused |
Pupils that do not respond to light | When the eyes are opened, the pupils do not react to light |
No movement except reflexes | The body is still; only involuntary reflexes may remain |
No response to pain or loud noises | Even strong stimuli produce no reaction |
No speech, communication or awareness | The person cannot talk or show any sign of understanding |
Slow, irregular or gasping breathing | Breathing patterns become abnormal |
Loss of consciousness | Complete unawareness of self and surroundings |
What Causes a Coma?
A coma results from anything that disrupts how the brain works. Common causes include lack of oxygen or blood flow to the brain, brain tumors, extreme body temperatures (very high or very low), head injuries, brain infections such as meningitis and encephalitis, metabolic problems including abnormal blood sugar [5], liver failure and kidney failure, prolonged seizures (status epilepticus) [5], stroke, and substance overdose involving opioids or alcohol.
Risk Factors
Anyone can fall into a coma, but certain conditions raise the risk significantly.
Risk factor | Why it matters |
Substance use disorder | Overdose risk, especially opioids and alcohol |
Diabetes | Dangerous swings in blood sugar can shut down brain function |
Epilepsy or seizure disorders | Prolonged seizures (status epilepticus) can cause coma |
Heart problems | Cardiac arrest cuts off oxygen to the brain |
High blood pressure or cholesterol | Raises stroke risk |
Low thyroid levels (hypothyroidism) | Severe cases can disrupt metabolism enough to trigger coma |
Safety behavior also matters. Risk rises when people skip a helmet during biking, motorcycling or contact sports, or ride without a seatbelt in a car, because trauma is one of the leading causes of coma.
What Happens in the Body?
While a person is in a coma, they cannot care for themselves and need around-the-clock medical support: a feeding tube for nutrition, a urinary catheter, and often a ventilator to help them breathe. The coma itself, and the care it requires, can produce additional complications.
Complication | How it develops |
Pressure injuries (bedsores) | Immobility reduces blood flow to skin |
Blood clots | Lack of movement slows circulation |
Delirium | Prolonged unconsciousness disrupts normal brain activity |
Infections | Pneumonia from ventilators; urinary tract infections from catheters |
Muscle loss (atrophy) and weakness | Muscles waste without movement |
Death is also a possible complication, especially with severe injuries, serious illness, or delayed medical care.
How Is a Coma Diagnosed?
Coma care begins the moment the person arrives. Providers immediately check vital signs (breathing, heart rate and blood pressure) and treat obvious emergencies on the spot: IV sugar (dextrose) for low blood sugar, or an opioid-reversal injection (naloxone) if an overdose is suspected [5].
A physical and neurological exam follows, along with the Glasgow Coma Scale (GCS), the standard tool for measuring severity [2]. The GCS scores three responses (eye opening 1 to 4, motor response 1 to 6, and verbal response 1 to 5) for a total of 3 to 15. A score of 15 means fully alert, and a score of 8 or below is generally considered severe impairment consistent with a coma.
Coma vs. Persistent Vegetative State vs. Other Disorders of Consciousness
The terms used to describe reduced consciousness can be confusing. The table below clarifies how they differ.
State of consciousness | Description |
Coma | Loss of consciousness; the person is unaware and unresponsive with eyes closed |
Vegetative state | Awake (eyes may open) but unaware of self and surroundings |
Persistent vegetative state | A vegetative state lasting more than one month |
Minimally conscious state | Limited, inconsistent signs of awareness |
Confusional state | Some awareness, but disoriented and confused |
Brain death | Complete and irreversible loss of all brain function |
A medically induced coma is different again: it is deliberately created and closely controlled in a medical setting, usually to give an injured brain time to rest and heal.
Treatment: How Care Teams Manage a Coma
Treatment happens on three tracks at once, and the care team tracks progress with the Glasgow Coma Scale. A companion tool, the Coma Recovery Scale, measures body movement, eye movement, sounds and speech, and responses to touch and pain. Even tiny signs of awareness, such as the eyes following an object, are important because they help the team choose the right treatments to support recovery.
Treatment track | What it involves |
Making the person safe | A ventilator supports breathing; IV fluids support the circulation |
Handling emergencies | IV dextrose for low blood sugar; naloxone for suspected overdose; antiseizure medications |
Managing the cause | Antibiotics for infections; surgery for head injuries; medications for heart problems, all aimed at preventing complications |
What Is the Outlook?
Because a person in a coma is not conscious, they do not know they are in one. There are no signs of awareness, although some reflex responses may remain depending on the depth of the coma. A coma can be brief, but it rarely lasts more than two to four weeks [6]. After that, people either wake up or shift into a different state of reduced consciousness, such as a vegetative or minimally conscious state. Some people remain in a coma for much longer, and for them infection, such as pneumonia, is the most common cause of death [6].
Can a person in a coma hear or remember? Possibly. Some people can hear what is happening around them and remember parts of it later. The experience varies a great deal from person to person and is hard to predict, which is why families are encouraged to keep talking to their loved one.
No two comas are the same. Many causes produce many different outcomes [5] [6]: some people wake up quickly, while others take longer or need more support. A provider who knows the specific case is best placed to explain what to expect.
Planning Ahead: Advance Directives
Because a person in a coma cannot make decisions, loved ones must make medical choices on their behalf. Completing an advance directive, and naming a medical power of attorney, before an emergency happens means your wishes guide your care when you cannot speak for yourself.
When to Seek Emergency Care
A coma is itself the emergency. Call emergency services immediately if someone cannot be woken up, does not respond to pain, or has irregular or gasping breathing. Anyone at higher risk, such as people with diabetes, seizure disorders, heart conditions, or substance use disorder, should stay on top of treatment for their underlying condition and wear helmets and seatbelts without exception.
Living With a Loved One in a Coma
Families play a real role. Talk to your loved one regularly, because some people in a coma can hear and later remember voices. Work closely with the care team as they track eye, movement and speech responses, because even small signs of awareness shape treatment decisions. Prepare for a hospital stay that may last weeks, and use that time to gather medical history and any advance directives that exist.
Conclusion
A coma is a deep state of unconsciousness: a medical emergency, not a diagnosis. It signals that something has disrupted the brain systems that keep us awake, whether that is head trauma, oxygen loss, stroke, infection, overdose, seizure, or a metabolic crisis. Care teams respond on three fronts at once: stabilizing the body, reversing immediate dangers, and treating the root cause, while tracking every small sign of returning awareness. Most comas end within a few weeks, and even voices from loved ones may be heard and remembered along the way. If you or someone you love carries risk factors such as diabetes, epilepsy, or heart disease, stay on top of treatment and make your advance directives known, because preparation is one of the few things within your control.
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Frequently Asked Questions
What exactly is a coma?
A coma is a deep state of unconsciousness where a person cannot wake up or respond, even to pain or loud sounds. They are unaware of what is happening around them.
Is a coma a medical emergency?
Yes. A coma is always a medical emergency that requires immediate attention, because delaying treatment can lead to serious complications or life-threatening outcomes.
How long does a coma last?
A coma rarely lasts more than two to four weeks. It can be brief, and many end sooner, but some people remain in a coma for much longer.
What happens after a coma?
People in a coma usually either wake up or shift into a different state of reduced consciousness, such as a vegetative state or a minimally conscious state.
What is the difference between a coma and a vegetative state?
In a coma the eyes stay closed and there is no awareness or wakefulness. In a vegetative state the person may open their eyes and appear awake but remains unaware of themselves and their surroundings.
What is a persistent vegetative state?
It is a vegetative state that lasts more than one month.
What is the difference between a vegetative state and a minimally conscious state?
A minimally conscious state involves limited, inconsistent signs of awareness, while a vegetative state shows none.
Can a person in a coma hear you?
Possibly. Some people in a coma can hear what is happening around them and remember parts of it later, although this varies widely and is hard to predict.
Should I talk to someone in a coma?
Yes. Because some people can hear and remember voices, families are encouraged to keep talking to their loved one.
What causes a coma?
Common causes include lack of oxygen or blood flow to the brain, brain tumors, extreme body temperatures, head injuries, brain infections like meningitis and encephalitis, metabolic problems, seizures, stroke, and drug or alcohol overdose.
Can low blood sugar cause a coma?
Yes. Both very low and very high blood sugar levels can cause a diabetes-related coma.
Can a drug overdose cause a coma?
Yes. Overdoses, especially involving opioids or alcohol, can trigger a toxic-metabolic coma.
Can a heart attack lead to a coma?
Indirectly, yes. Cardiac arrest stops blood flow to the brain, causing an anoxic brain injury that can result in a coma.
Can drowning cause a coma?
Yes. Drowning deprives the brain of oxygen and can cause an anoxic brain injury leading to coma.
What is an anoxic brain injury?
It is brain damage caused by lack of oxygen or blood flow to the brain, one of the main types of coma.
What is a medically induced coma?
It is a controlled coma created in a medical setting to help the brain rest and heal, usually after severe injury or illness.
What is trauma-induced coma?
A coma caused by a serious head injury.
Can extreme heat or cold cause a coma?
Yes. Both very high and very low body temperatures can disrupt brain function enough to cause a coma.
Can seizures cause a coma?
Yes. Prolonged seizures, known as status epilepticus, can trigger a coma.
Can infections cause a coma?
Yes. Brain infections such as meningitis and encephalitis are known causes.
Can liver or kidney failure cause a coma?
Yes. Metabolic problems including liver failure and kidney failure can disrupt the chemicals that keep the brain working normally.
What is the reticular activating system?
It is a network of nerve cells in the brainstem that keeps you awake. Comas occur when this system, the cerebral hemispheres, or both are disrupted.
What are the cerebral hemispheres?
They are the two largest areas of the brain, responsible for thinking.
Who is at higher risk of falling into a coma?
People with substance use disorder, diabetes, epilepsy or seizure disorders, heart problems, high blood pressure or cholesterol, and severe hypothyroidism.
Does not wearing a helmet increase coma risk?
Yes. Skipping a helmet during biking, motorcycling or contact sports, and riding without a seatbelt, raise the risk because trauma is a leading cause.
How is coma severity measured?
With the Glasgow Coma Scale (GCS), which scores eye, motor and verbal responses from 3 to 15. A score of 8 or below is generally considered severe impairment consistent with a coma.
What does a GCS score of 15 mean?
Fully alert and responsive.
How do doctors diagnose the cause of a coma?
Through lab tests on blood, urine and spinal fluid, CT or MRI imaging of the brain, EEG brain activity monitoring, and EKG heart rhythm checks.
What is the first thing doctors do in the emergency room?
They check vital signs (breathing, heart rate and blood pressure) and treat immediate emergencies such as giving IV sugar for low blood sugar or naloxone for a suspected overdose.
What is naloxone?
A medication that reverses the effects of an opioid overdose, often given as an injection in the emergency room.
What is dextrose used for in coma care?
It is IV sugar given to quickly correct dangerous low blood sugar.
Can a coma be treated?
Treatment focuses on three tracks: keeping the person safe with breathing and IV support, handling emergencies immediately, and managing the underlying cause to prevent complications.
Why do people in comas need a ventilator?
Because they often cannot breathe on their own, a ventilator supports their breathing.
Why do people in comas need a feeding tube?
Because they cannot eat or drink, nutrition is delivered through a tube.
What complications can develop during a coma?
Pressure injuries (bedsores), blood clots, delirium, infections such as ventilator pneumonia and catheter-related urinary tract infections, and muscle loss with weakness.
Can a coma be fatal?
Yes. Death is a possible complication, more likely with severe injuries, serious illness, or delayed medical care.
Do people in a coma feel pain?
A person in a coma does not respond to pain and is, by definition, unaware. Because awareness can be hard to judge from the outside, care teams still assess and treat possible pain, especially when unresponsiveness lasts longer.
Can someone in a coma move?
Only reflex movements are possible. There is no purposeful movement.
What is the Coma Recovery Scale?
A tool that measures body movement, eye movement, sounds and speech, and responses to touch and pain to track signs of returning awareness.
Are small signs of awareness important?
Yes. Even subtle signs like the eyes following an object help the care team choose the right treatments to support recovery.
Is a persistent vegetative state permanent?
Not necessarily. People can transition into a minimally conscious state or wake up, though the longer a state persists, the more careful providers are about expectations.
What is brain death?
The complete and irreversible loss of all brain function, which is distinct from coma and vegetative states.
What is a confusional state?
A state of some awareness that is accompanied by disorientation and confusion.
Can children recover from a coma?
Recovery depends on the cause and severity of the brain injury. A provider familiar with the case is best placed to explain expectations for any patient, child or adult.
How can families support someone in a coma?
By talking to them regularly, working closely with the care team, gathering medical history, and locating any advance directives.
What is an advance directive?
A document that states your medical care wishes in advance, so loved ones can guide treatment if you cannot.
What is a medical power of attorney?
A person you designate to make medical decisions for you if you become unable to.
Why should I complete an advance directive?
Because if you fall into a coma, loved ones must make medical decisions on your behalf, and an advance directive ensures your wishes are followed.
Can diabetes be managed to prevent coma?
Staying on top of treatment for blood sugar is one of the best ways to reduce the risk of a diabetes-related coma.
Is there a cure for coma?
There is no cure as such. Treatment focuses on protecting the brain, reversing emergencies, and treating the cause while the brain heals.
Will someone in a coma know they are in a coma?
No. Because they are not conscious, they do not know they are in a coma.
Can someone recover fully from a coma?
Some people wake up quickly and recover well; others take longer or need more support. Outcomes vary widely by cause and severity.
What should I do if someone cannot be woken up?
Call emergency services immediately.
Related Reading
Stroke: Symptoms, Causes, Diagnosis, and Treatment — A Complete Guide
Understanding Meningitis: Symptoms, Causes, and Emergency Care
Hypoglycemia: Managing Low Blood Sugar Emergencies and Prevention
Hyperglycemia in Diabetes: Warning Signs, Target Numbers, and When It Becomes an Emergency
Understanding Opioid Overdose: Recognition, Emergency Response, and Prevention
Learn more in our guide to Glasgow Coma Scale (GCS): Scoring Chart, What Scores Mean and GCS-P.
References
Giacino JT, Katz DI, Schiff ND, et al. Practice guideline update recommendations summary: disorders of consciousness: report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology; the American Congress of Rehabilitation Medicine; and the National Institute on Disability, Independent Living, and Rehabilitation Research. Neurology. 2018;91(10):450-460. PMID 30089618. https://doi.org/10.1212/WNL.0000000000005926
Teasdale G, Maas A, Lecky F, et al. The Glasgow Coma Scale at 40 years: standing the test of time. Lancet Neurol. 2014;13(8):844-854. PMID 25030516. https://doi.org/10.1016/S1474-4422(14)70120-6
Gams Massi D, Kedonkwo Mbogne AH, Siysi VV, et al. Outcome of non-traumatic coma in a tertiary referral hospital in Cameroon. Afr J Emerg Med. 2024;14(3):179-185. PMID 39301466. https://doi.org/10.1016/j.afjem.2024.06.003
Boly M, Sanders RD, Mashour GA, et al. Consciousness and responsiveness: lessons from anaesthesia and the vegetative state. Curr Opin Anaesthesiol. 2013;26(4):444-449. PMID 23743554. https://doi.org/10.1097/ACO.0b013e3283628b5d
Huff JS, Tadi P. Coma. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; updated July 3, 2023. PMID: 28613473. https://www.ncbi.nlm.nih.gov/books/NBK430722/
National Library of Medicine. Coma. MedlinePlus. Last updated November 30, 2025. https://medlineplus.gov/coma.html
Medical disclaimer
This content is for general informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider for diagnosis and treatment of any medical condition. A coma is a medical emergency, so call emergency services immediately if someone cannot be woken up or does not respond.
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