An Overview of Level of Consciousness (LOC)

LOC is an abbreviation describing patient awareness, alertness, and wakefulness

Level of consciousness (LOC) is a medical term used to describe how awake, alert, and aware you are. It also refers to how well you respond to attempts to get your attention. A person with an altered level of consciousness may have decreased cognitive function or be difficult to arouse.

A variety of medical conditions and drugs can affect your level of consciousness, from having dementia or lethargy, to being in a coma. Sometimes impaired consciousness is reversible, while other times it is not.

This article covers normal and altered states of consciousness as well as coma classifications.

A man laying in a coma in the hospital
Caiaimage / Sam Edwards OJO+ / Getty Images

Normal Level of Consciousness

Medical definitions say a normal LOC means you're either awake or can be readily awakened from normal sleep. Terms include:

  • Consciousness: A state in which you're awake, aware, alert, and responsive to stimuli.
  • Unconsciousness: A state in which you have a deficit in awareness and responsiveness to stimuli (touch, light, sound).

Sleeping isn't considered unconsciousness if waking up would result in normal consciousness.

Between these two extremes are several altered levels of consciousness. They range from confusion to coma, each with its own definition.

Altered Level of Consciousness

Altered or abnormal levels of consciousness are states in which you either have decreased cognitive function or can't be easily aroused.

Most medical conditions affect the brain and impair consciousness when they become serious or life-threatening. An altered LOC usually signals a serious medical problem.

Often, an altered LOC can deteriorate rapidly from one stage to the next. They require timely diagnosis and prompt treatment.


Confusion describes disorientation that makes it difficult to:

  • Reason
  • Provide a medical history
  • Participate in a medical examination

Causes include:


Delirium is a term for an acute confused state. It involves impaired cognition (thought processes) and may include:

  • Attention deficits
  • Sleep-wake cycle changes
  • Hyperactivity (agitation) or hypoactivity (apathy)
  • Hallucinations (seeing things that are not there) or delusions (false beliefs)
  • Heart rate and blood pressure instability

Causes can include:

  • Alcohol withdrawal
  • Recreational drugs
  • Medications
  • Illness
  • Organ failure
  • Severe infections

Lethargy and Somnolence

Lethargy and somnolence (sleepiness) involve:

  • Severe drowsiness
  • Listlessness
  • Apathy
  • Reduced alertness

A lethargic person may need a gentle touch or verbal stimulation before they'll respond. Causes can include severe illnesses or infections, recreational drugs, and organ failure.

Normal Wakefulness
Confusion  Disorientation
Inability to reason
Sleep deprivation
Seizure recovery
Delirium  Impaired cognition
Agitation or apathy
Unstable heart rate and blood pressure
Alcohol withdrawal
Organ failure
Severe infections
Lethargy and somnolence Severe drowsiness
Reduced alertness
Severe illness
Severe infection
Drug use
Organ failure
Obtundation Reduced alertness
Slow responses to stimuli
Prolonged periods of sleep
Drowsiness while awake
Brain swelling
Blood infection
Advanced organ failure
Stupor Minimal response to vigorous stimuli Stroke
Drug overdose
Lack of oxygen
Brain swelling
Heart attack
Coma  Unresponsiveness to all stimuli
May lack gag reflex, pupil response
Severely diminished brain function
Extreme blood loss
Organ failure
Brain damage


Obtundation is reduced alertness with:

  • Slow responses to stimuli
  • Needing repeated stimulation to maintain attention
  • Prolonged periods of sleep
  • Drowsiness between these periods

Causes can include:

  • Poisoning
  • Stroke
  • Brain edema (swelling)
  • Sepsis (a blood infection)
  • Advanced organ failure


If you're in a stupor, you respond minimally to vigorous stimulation, such as a pinched toe or light in the eyes.

Causes can include:


Someone in a coma doesn't respond to any stimuli. Their pupils may not react to light, and they may not have a gag reflex.

Comas are caused by severely diminished brain function. This is usually due to:

  • Extreme blood loss
  • Organ failure
  • Brain damage

The causes of these altered LOC may overlap. For example, the early stages of brain edema or organ failure can cause confusion. But you can then advance rapidly through the stages of lethargy, obtundation, stupor, and coma.

Classifications of Coma

Levels of consciousness can be subdivided into levels that further clarify your degree of unresponsiveness. Several systems have been developed to standardize these classifications. That helps improve communication among healthcare providers and aids in research.

The most common classification systems are:

  • Grady Coma Scale: Grades a coma from I to V. It's based on your state of awareness and response to stimuli (your name being called, light pain, deep pain). Grade I indicates confusion, while V indicates coma (no response to stimuli).
  • Glasgow Coma Scale: Scores the level of consciousness from 1 to 15, with 15 being normal LOC. This scale takes into account verbal, motor, and eye responses to stimuli.


Levels of consciousness range from normal alertness and attention through many altered states. It starts with confusion and delirium to stupor and coma.

The same things may cause a milder state of altered LOC that can cause more severe states. Sometimes, you may start with a mild state and rapidly progress through to a higher stage.

Coma scales can help describe the exact level of consciousness.

A Word From Verywell

If you or someone you know has an altered state of consciousness, it's important to get medical help. These states don't come on without a reason, and most causes pose real threats to your health.

If you're at risk for altered LOC, be sure you have the proper medical precautions in place. For example, wear a medical alert bracelet or have an app on your phone that lists your diagnoses, medications, and emergency contacts. Some can be accessed even when your phone is locked.

You may also want to designate a healthcare proxy to speak for you when you're unable. This is especially important if your close family members don't agree with your wishes.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Tufts Medical Center. Altered level of consciousness.

  2. Cleveland Clinic. Delirium.

  3. Merck Manual Professional Version. Overview of coma and impaired consciousness.

  4. Opara JA, Małecka E, Szczygiel J. Clinimetric measurement in traumatic brain injuries. J Med Life. 2014;7(2):124-127.

  5. Reith FCM, Lingsma HF, Gabbe BJ, Lecky FE, Roberts I, Maas AIR. Differential effects of the Glasgow Coma Scale Score and its components: An analysis of 54,069 patients with traumatic brain injury. Injury. 2017;48(9):1932-1943. doi:10.1016/j.injury.2017.05.038

Additional Reading

By Angela Morrow, RN
Angela Morrow, RN, BSN, CHPN, is a certified hospice and palliative care nurse.