Why Do I Black Out When I Drink? Effects Explained

Blacking out is a scary and often unintended consequence of heavy drinking or binge drinking. If you experience blackouts, otherwise known as alcohol-related memory loss, you are not alone. Research shows that as many as 50 percent of people who drink experience blackouts. While blackouts are common, they are also dangerous. With the right information, time, and support, you can stop experiencing blackouts for good. 

We spoke to Dr. Kristine De Jesus about the causes of blackouts, what happens during a blackout, and how to prevent them from occurring.

What is Blackout Drinking?

Blackout drinking is a term used to describe when a person experiences mild to complete memory loss during part of, or all of, a drinking event. According to the National Institute on Alcohol Abuse and Alcoholism (NIAAA), blackouts produce a gap in memory transfer, known as memory consolidation, in the brain’s hippocampus.

What’s particularly problematic and potentially dangerous about blackouts is that a person is still conscious and can still engage with their environment—it’s just that the memory doesn’t make a recording of the event. That’s why people may wake up in the morning either completely unaware of what happened the night before, or only with a partial memory.

We asked Dr. Kristine De Jesus, PsyD, why blackouts occur. She explained, “A blackout occurs after a period of alcohol use when the concentration of alcohol in the blood is high and the body is trying to reduce harm by streamlining bodily functions.” 

This explains why a person is still conscious and can interact with their surroundings and even have detailed conversations. During a blackout, the body focuses on more critical functions than memory. “Recording new memories is not essential to sustain life, therefore the body prioritizes the functions of the autonomic nervous system over the production of recording memories in order to preserve life,” says De Jesus.

"how alcohol affects memory. Short-term memory loss: alcohol slows nerve activity in the hippocampus and inhibits memory formation. This can create partial or complete blackouts. Long-term memory loss: extended alcohol use can damage and destroy nerve cells in the hippocampus, leading to dementia or permanent memory loss"

What Happens When I Black Out?

You might be wondering, under what circumstances will I black out, and what exactly happens in my body if I do? Dr. De Jesus explains that blackouts are generally associated with high Blood Alcohol Content (BAC)

“Blackouts generally occur when a person’s BAC is upwards of 0.14 (14% of the blood contains alcohol). However, science suggests that the threshold for blackouts varies from person to person.” 

At this blood alcohol level, you might feel euphoric at first, before ultimately feeling unpleasant. Because of how alcohol makes you feel drunk, you might find you struggle to walk or stand, and your judgment might be significantly impaired. Sometimes you may remember snippets of the night before, and other times recall nothing at all. This is because there are two types of blackouts: partial (fragmentary) or complete (en-bloc) blackouts. 

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En-bloc blackouts are characterized by complete memory loss and typically occur at a BAC of 0.14 or higher. Fragmentary blackouts cause a partial memory loss, and are also sometimes referred to as brownouts. Researchers at Wetherill and Fromme (2016) state that fragmentary blackouts are more common, and typically occur with a BAC of 0.06-0.14.

Blackouts were a real part of my acute alcohol use disorder, starting in my late teens and continuing through to my early twenties. I recall waking up in the morning and having a routine of checking my phone to see who I’d called, texted, or interacted with. Next, I’d check to see if there were any pictures that gave a clue to where I’d been. Then I’d scour my apartment to try and patch together a picture of what had happened the night before. Often I’d find myself covered in bruises and be wearing clothing I didn’t recall putting on, or I’d find a trail of clothes throughout my apartment. I think worse, though, was the shame I felt for drinking so much that I couldn’t remember what happened to me. Understanding the risk factors that lead to blackouts can help minimize self-blame and help you change your drinking.

What Increases the Risk of Alcohol Blackouts?

Social pressure is one of the primary drivers of blackout drinking, and is especially prevalent on college campuses. When you’re surrounded by social groups where blackout drinking is normalized, it can be difficult to see the signs you’re drinking too much. Certainly, in my case, heavy drinking was normalized. It was considered a rite of passage with my friends while growing up, and later with co-workers going to the bar after work. Drinking after work, and sometimes during a Friday afternoon or lunchtime, was the culture I was engaged in for nearly every job I had. It wasn’t until I started looking after my mental health that I realized I could reduce harm around my drinking.

Some other factors that increase the risk of blackouts include:

  • Drinking to numb chronic pain
  • Drinking on an empty stomach 
  • Drinking to escape difficult emotions, like grief
  • Consuming large amounts of alcohol in a small amount of time  

"How can you tell when 'normal partying' becomes problematic?"

Short Term and Long Term Effects of Blacking Out

There are many short and long term effects of blackout drinking. In the short-term, the risks include:

Blackout drinking can also have long-term effects, because the body is exposed to more alcohol at once than it has the ability to process. Some of the long-term effects of unhealthy alcohol use include:

  • Weakened immune system
  • Liver disease
  • Risk of high blood pressure, stroke, and heart disease
  • Cancer of the breast, mouth, throat, esophagus, voice box, colon, liver, and rectum
  • Mental health problems, like depression and anxiety
  • Social and work-related problems 
  • Significant damage to parts of the brain responsible for memory, cognitive function, muscle coordination, decision making, and impulse control. 
  • Wernicke-Korsakoff Syndrome, which causes mental confusion, paralysis of eye nerves, and problems with muscle coordination. 

How to Apply Harm Reduction to Blackout Drinking

I asked Dr. De Jesus what measures a person can put in place to prevent blacking out when drinking. Her suggestions include:

  • Limiting alcohol consumption to one serving of alcohol per hour (as that is the amount the body can metabolize and process through the liver without getting overwhelmed) 
  • Alternating between alcoholic and non-alcoholic drinks  
  • Being mindful of how much alcohol is in a drink (not all drinks are created equal and some have more alcohol than others)
  • Tracking the servings of alcohol one has consumed (make a note in your phone, or count the straws if possible)
  • Exploring other strategies for mindful drinking

Working with a therapist is another effective way to build a plan to prevent blackout drinking. Your therapist can share strategies for moderation or sobriety, and help you work through any underlying issues that were leading to blackouts in the first place.

A Note on Tolerance

“People rarely understand the notion of tolerance,” contends De Jesus. She explained that individuals generally assume tolerance is how much alcohol a person can handle. But most people don’t know that although tolerance can change the way an individual feels, it doesn’t affect one’s BAC. 

“BAC is a mathematical constant. The amount of alcohol, time in which it is consumed, gender, and weight of the person determine BAC, whereas tolerance is the time in which the body shows the impact of BAC.” The BAC level that causes an individual to blackout will remain roughly the same throughout their lifetime, no matter their tolerance. This is also important to keep in mind when it comes to driving or anything else that requires you to be under a certain limit of BAC. In brief, even if your tolerance increases, your risk of blacking out will remain the same. 


Alcohol can change our brain chemistry in a way that makes it difficult to stop drinking without outside help. At Monument, you can access treatment options like medication to stop drinking, therapy, and support groups all from the comfort of your own home. We believe that all of you matters when you’re thinking about quitting drinking, and our online alcohol treatment program and community are designed to address it all.

Disclaimer: Our articles and resources do not constitute clinical or licensed therapy or other health care services. If you need counseling or therapy services please contact a licensed provider. If this is a medical emergency, call 911.

About the Author

Olivia PennelleOlivia Pennelle (Liv) is an experienced writer, content strategist, and peer mentor located outside of Portland, Oregon. She has been writing in the recovery and mental health space for ten years, leading her to pursue a masters in clinical social work, which she hopes to complete by summer 2023. Liv believes passionately that we all deserve access to recovery and that we need to make space in the field for more expansive and self-directed pathways of recovery. She founded the growing community Life After 12-Step Recovery. Liv identifies as Queer, a person in long-term recovery, a dog mom, and is a bit of an iconoclast. You can find her writing across the web in publications like STAT News, The Temper, Ravishly, Shondaland, Filter, OAR, Workit Health, Faces and Voices of Recovery, and most recovery organizations' blogs.