Medically Reviewed By William C. Lloyd III, MD, FACS

What are blackouts?

Blackouts are periods of unconsciousness or memory loss. Generally, a blackout is described as a period of unconsciousness or lack of awareness when you are unable to recall what happened or what you did. Blackouts may occur as a result of brain damage, drug side effects, excessive alcohol consumption, or disorders affecting brain function, such as epilepsy. Fainting, also known as syncope, is a term used to refer to a blackout. Conditions that can cause syncope include cardiac arrhythmias (abnormal heart rate or rhythm), abnormalities of the heart muscle or valves, or a condition called postural hypotension, in which a person faints after standing up quickly from a lying position and there is insufficient blood flow to the brain at that point.

A generally harmless form of blackout is known as vasovagal syncope. In this condition, there is a disruption in the balance of neurotransmitters that regulate the blood vessels and heart rate, causing a temporary decrease in blood flow to the brain. This is a common cause of fainting that may even occur as a reaction to stressful or frightening situations. Typically, full consciousness promptly returns.

Blackouts can also be due a recent traumatic event, in which case you may forget everything that happened right before or right after the event (anterograde amnesia). Unexplained blackouts, or blackouts that appear to be due to injury or trauma, should be evaluated by a medical professional.

Blackouts may occur with a variety of other symptoms, depending on the underlying cause or disorder. Sometimes, the memories from blackouts can be recovered, while other times, they cannot. It is also possible that blackouts can lead to problems forming new memories.

Seek immediate medical care (call 911) for memory loss that occurs with head injury or trauma, high fever (higher than 101 degrees Fahrenheit), uncontrolled or heavy bleeding, loss of consciousness, or seizure. Seek immediate medical care (call 911)if you believe a person may have alcohol poisoning or may be suffering from a drug overdose.

If your blackouts recur or cause you concern, seek prompt medical care.

What other symptoms might occur with blackouts?

Blackouts may accompany other symptoms, which vary depending on the underlying disease, disorder or condition.

Nervous system symptoms that may occur along with blackouts

Blackouts may accompany other symptoms affecting the brain and nervous system including:

Other symptoms that may occur along with blackouts

Blackouts may accompany symptoms related to other body systems including:

Serious symptoms that might indicate a life-threatening condition

In some cases, blackouts may be a symptom of a life-threatening condition that should be evaluated immediately in an emergency setting. Seek immediate medical care (call 911) if you, or someone you are with, have any of these life-threatening symptoms including:

What causes blackouts?

Blackouts may arise from a variety of conditions or events that affect the brain. Often, blackouts will result from a traumatic event or an event that involves head injury.

Traumatic causes of blackouts

Blackouts may often be caused by trauma to the head or brain including:

    Substance-related causes of blackouts

    Blackouts can also be caused by a variety of drugs and other substances including:

    • Alcohol intoxication

    • Medication side effects, such as the side effects of cancer treatments or seizure medications, or agents used for anesthesia

    • Poisons, such as cleaning chemicals or pesticides

    • Recreational drug use

    Disease and disorder causes of blackouts

    Blackouts can be caused by different diseases and disorders including:

    • Anemia

    • Brain or spinal cord injury or tumor

    • Cardiac arrhythmia

    • Dehydration (loss of fluids and electrolytes, which can be life threatening when severe and untreated)

    • Dementia

    • Depression

    • Encephalitis (inflammation and swelling of the brain due to a viral infection or other causes)

    • Epilepsy (disorder characterized by recurrent seizures)

    • Infections of the brain

    • Nutrient deficiency

    • Parkinson’s disease (brain disorder that impairs movement and coordination)

    • Postural hypotension

    • Vasovagal syncope

    Serious or life-threatening causes of blackouts

    In some cases, blackouts may be a symptom of a serious or life-threatening condition that should be evaluated immediately in an emergency setting. These include:

    Questions for diagnosing the cause of blackouts

    To diagnose your condition, your doctor or licensed health care practitioner will ask you several questions related to your blackouts including:

    • Can you remember things that happened recently?

    • Do you remember what you did after your blackout?

    • Do you remember what you were doing before your blackout?

    • Have you ever had a seizure?

    • Have you had any recent injuries or surgeries?

    • What medications are you taking?

    • What other symptoms occurred with your blackout?

    • When did your blackout occur?

    • When was your last drink of alcohol?

    What are the potential complications of blackouts?

    The potential complications of blackouts depend on the underlying cause. Because blackouts can be due to serious diseases, failure to seek treatment can result in serious complications and permanent damage. Once the underlying cause is diagnosed, it is important for you to follow the treatment plan that you and your health care professional design specifically for you to reduce the risk of potential complications including:

    • Brain damage
    • Injury during a blackout episode
    • Neurological problems, such as memory loss and confusion
    • Permanent nerve damage, including paralysis
    Was this helpful?
    1. Memory loss. Medline Plus, a service of the National Library of Medicine National Institutes of Health.
    2. Amnesia. University of Iowa Hospitals and Clinics Health Topics.
    Medical Reviewer: William C. Lloyd III, MD, FACS
    Last Review Date: 2021 Jan 8
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