A blackout is a temporary condition that affects your memory. It’s characterized by a sense of lost time.

Blackouts occur when your body's alcohol levels are high. Alcohol impairs your ability to form new memories while intoxicated. It doesn't erase memories formed before intoxication.

As you drink more alcohol and your blood alcohol level rises, the rate and length of memory loss will increase. The amount of memory loss varies from person to person.

Memory loss, or a blackout, is thought to occur when your blood alcohol content reaches 14 percent or higher. You may not have any memory of the time that’s passed when your blood alcohol content is above that threshold.

During this time, you may experience:

  • difficulty walking
  • difficulty talking
  • difficulty standing
  • impaired judgement
  • impaired vision

There are several factors that can affect your blood alcohol level, including:

  • weight
  • gender
  • the type of alcohol consumed
  • how quickly the alcohol is consumed

It’s important to note that there isn’t a set number of drinks that can trigger a blackout. It all comes down to the amount of alcohol in each drink you’ve consumed and the way the alcohol affects you.

There are two types of blackouts: partial and complete.

If you experience a partial blackout, visual or verbal cues may help you remember forgotten events.

If you have a complete blackout, memory loss is permanent. Even with cues, you’re unlikely to remember what happened during this time.

The nature of blackouts makes it difficult for researchers to examine the correlation between memory recall and blackout type.

Blackouts are often associated with alcohol consumption. For many people, drinking too much alcohol too quickly, or on an empty stomach, can cause a blackout.

A blackout can also be caused by:

  • epileptic seizures
  • fainting
  • low blood pressure
  • psychogenic seizures
  • low blood sugar
  • certain medications
  • oxygen restriction

A 2006 study found that temporary memory loss caused by a fall in blood pressure (syncope) is a more likely cause of nonalcoholic-induced blackouts.

Alcohol impairs your ability to walk, speak, react, and remember events. It also lowers inhibition, hinders impulse control, and affects decision-making.

The reward pathway in the brain regulates these activities. Although this part of the brain can build up long-term tolerance to alcohol, this isn’t true of the hippocampus.

The hippocampus is found deep within the brain. It’s critical to forming memories. The hippocampus can’t develop long-term alcohol toleration. This means it can’t create memories when a blackout occurs.

It's important to remember that a blackout isn’t the same as passing out. Someone who passes out has either fallen asleep or become unconscious because they consumed too much alcohol.

During a blackout, an intoxicated person can still function as normal. They may seem articulate because most parts of the brain are alcohol-tolerant. They can still eat, walk, hold conversations, have sex, drive, and get into fights. They just can't record any of the memories.

This seemingly aware state can make it difficult for other people to recognize if a person is in a blackout.

Heavy drinking may have lasting effects on the brain. These effects range in severity from momentary “slips” in memory to permanent, debilitating conditions. It’s thought that chronic alcohol consumption can harm the frontal lobe. This is the part of the brain that controls cognitive function. The frontal lobe also plays a role in short-term and long-term memory formation and recall.

Regular damage to the frontal lobe can impair your behavior and personality, how you perform tasks, and how you keep information. It’s thought that binge drinking can impair this part of your brain.

Binge drinking can affect your ability to:

  • walk steadily
  • make decisions
  • control impulses.

You may also experience:

  • headaches
  • dry mouth
  • nausea
  • diarrhea

Having even one blackout can be dangerous. According to the National Institute on Alcohol Abuse and Alcoholism, alcohol delays signals in the brain that control the gag reflex and other autonomic responses. A person who has blacked out or overdosed on alcohol could throw up while sleeping due to the loss of reflex control. This could cause them to choke and suffocate on their vomit.

A blackout also makes you more susceptible to injury, such as from a fall or car crash.

Taking sedatives while also consuming alcohol can increase the likelihood that you'll black out. That's because benzodiazepines like alprazolam (Xanax), and opioids like oxycodone (OxyContin), activate the GABA neurotransmitter. This causes your body to slow down and become more relaxed. Like alcohol, sedatives can impair your ability to think and make memories.

THC, the psychoactive compound found in marijuana, may also increase blackouts when combined with alcohol.

Learn more: Alcohol and anxiety »

Most reports suggest middle-age males with alcoholism are more likely to black out. Yet, anyone drinking large amounts of alcohol is at risk for blackouts.

Young adults in college are also considered at risk. Researchers link that risk to the heavy drinking habits common among many college students.

Studies have also found that women may be at greater risk of blackouts even though they generally drink less alcohol less frequently than men. This may be due to the physiological differences that affect alcohol distribution and metabolism. These include body weight, body fat percentage, and key enzyme levels.

Alcohol-induced blackouts differ from person-to-person. The amount you drink, how long it took you to drink, and your physiology play a role in your blackout. These factors also affect how long the blackout will last.

A blackout ends when your body finally absorbs the alcohol and your brain can make memories again. Sleep helps end blackouts because rest gives the body time to process the alcohol.

Others, though, can digest liquor while still awake. That means a blackout could last minutes to even days. Although many people recover from blackouts, one episode can be fatal.

In addition to abstaining from alcohol, moderation and pace are important to preventing blackouts. Avoid binge drinking, which is defined as consuming five or more drinks in about two hours for men, or four or more drinks for women.

To prevent blackouts, you should:

  • Eat a meal or heavy appetizers before and during alcohol consumption.
  • Drink slowly. Sipping, rather than gulping, can help you keep track of how alcohol is affecting your body.
  • Consider drinking a glass of water between alcoholic drinks to limit how much and how quickly you’re consuming alcohol.

Keep reading: Alcohol abuse and alcoholism, what are the differences? »