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Blood Alcohol Levels and Blackouts

What happened last night?  Ellen wakes up in her bed, she is somewhat confused, the daylight is blinding, and her mouth feels like cotton balls.  She rolls over to avoid the glaring morning light and discovers a naked male body in bed next to her; he is snoring.  Ellen feels a growing sense of panic.  She checks and is not wearing panties, or anything for that matter.  She wants to scream, but is afraid she will awaken the intruder.  She recalls meeting Angie at Gino’s.  Then what?  Nausea overwhelms her; she sneaks into the bathroom.  The stranger joins her in the bathroom, she doesn’t recognize a single feature of his face, but he reminds her they had a hell of a time together.  She is afraid to ask questions.  She doesn’t remember.  She is engaged to be married next week.  Later that afternoon Ellen goes to the police station to report that she was raped.  What happens now?

What Exactly is a Blackout? 

Alcohol can interfere with the brain’s ability to form new memories.  As the amount of alcohol consumed increases, so does the magnitude of the memory impairments. It is like a switch turns to off in the brain when a person’s blood alcohol content reaches a certain level.  Blackouts represent episodes at which time a subject participates in events that he/she later cannot remember.  This type of amnesia is referred to “alcohol related amnesia” and is very similar in character to other types of anterograde amnesia.  In these types of amnesia an individual cannot form new memories, but previous memories are not erased.  “En bloc” blackouts are stretches of time where the drinker has absolutely no memory at all.  Blackouts do not involve a loss of consciousness.  However, blackouts may precede passing out or losing consciousness.  A subject, who has usually consumed large quantities of alcohol rapidly, can still engage in complicated activities from holding a conversation, to driving, to dancing, to having sexual relations, etc.  However, he/she may not remember all, most, or even any of his/her actions or behaviors.  Recent studies indicate that blackouts are much more common among social drinkers (including college drinkers) than was previously assumed.  Fragmentary blackouts (often referred to as gray-outs or brown-outs) are episodes when the drinker’s memory is spotty.  They may remember some things, especially if reminded by others. 

The switch mentioned above is actually in a part of the brain called the hippocampus (located in the forebrain).  The hippocampus plays major roles in the formation of new memories related to experienced events, accessing previous memories, and spatial navigation (which is why an intoxicated individual staggers around).   Quite simply, alcohol disrupts the functioning of the hippocampus.  Prolonged and chronic alcohol abuse/dependence can permanently damage the hippocampus. This is one of the first regions of the brain to be damaged in Alzheimer's disease and Alcohol Wernicke-Korsakoff Syndrome (alcohol induced dementia)

Blood Alcohol Content

When a person consumes alcohol, it is absorbed in the stomach and small intestine.  After this absorption, the alcohol enters the bloodstream by dissolving into the water of the blood.  The rate of absorption depends on several factors:  the concentration of the alcohol, the type of alcohol, an empty versus full stomach, and gender.  Alcohol leaves the body in three ways:  5% is eliminated by the kidneys, 5% by the lungs (how breathalyzers measure alcohol levels), the rest is broken down by the liver into acetic acid.  Blood alcohol content (BAC) is the concentration of alcohol in blood. It is measured as mass per volume. For example, if a person has a BAC of 0.08% it means he/she has 0.02 grams of alcohol per 100 grams of his/her blood.  Generally, it takes one hour to eliminate one alcoholic drink.  (“And how big was that beer sir?”). 

The Effects of a Rising Blood Alcohol Level

(From the UCSD Student Health Services) 



0.02 - 0.03


You feel a little relaxed and maybe lightheaded. You haven't lost your coordination yet, but have a slight feeling of euphoria and some loss of shyness. Depressant effects are not apparent at this level.

0.05 - 0.06


You feel warm and relaxed and your feelings of shyness are disappearing. Some minor impairment of reasoning and memory, lowering of caution. Your behavior may become exaggerated: you talk louder or faster and act bolder than usual. Emotions are intensified, so your good moods are better and your bad moods are worse.

0.08 - 0.09


You believe you're functioning better than you actually are. You may start to slur your speech, your sense of balance is off, and your motor skills are starting to become impaired. Your ability to see and hear clearly is diminished. Your judgment is being affected, so it's difficult for you to decide whether or not to continue drinking. Your ability to evaluate sexual situations is impaired. Students may refer to this state of mind as "beer goggles", but this BAC can have serious repercussions.

0.10 - 0.12


You are having a significant impairment of motor coordination and loss of good judgment. Speech may be slurred; balance, vision, reaction time and hearing will be impaired. Your emotions are exaggerated, and some people become loud, aggressive, or belligerent. If you're a man, you may have trouble getting an erection at this BAC.

0.14 - 0.17


Gross motor impairment and lack of physical control. Blurred vision and major loss of balance. Your euphoric feelings may give way to unpleasant feelings. Your judgment and perception are severely impaired. You may become more aggressive, and there is an increased risk of accidentally injuring yourself or others. This is when you may experience a blackout.


You're feeling dazed and confused and may need help to stand or walk. If you injure yourself you may not feel the pain. If you are aware you've injured yourself, chances are you won't do anything about it. Some people have nausea and vomiting at this level. Your gag reflex is impaired and you can choke if you do vomit. Blackouts are likely at this level so you may not remember what has happened.


All mental, physical and sensory functions are severely impaired. You are emotionally numb at this point. There is an increased risk of asphyxiation from choking on vomit and of seriously injuring yourself by falls or other accidents.



You're in a stupor. You have little comprehension of where you are. You may pass out suddenly and be difficult to awaken. But don't kid yourself - passing out can also occur at lower BACs. But at lower BAC, you may decide you've had enough and go "pass out". With a BAC of .30%, your body will be deciding to pass out for you.


This is the level of surgical anesthesia. You may stop breathing at this point. Coma is possible.

0.40 + Up

You are probably in a coma. The nerve centers controlling your heartbeat and respiration are slowing down. There is a real possibility of death due to respiratory arrest.


Alcohol and Decision Making

At a high BAC more than just memory is impaired.  Alcohol effects judgment, decision-making, and impulse control.  Individuals often act out of character when intoxicated, and do things that they frequently later regret.  In a blackout, individuals are much more likely to engage in risky behaviors (crimes, drunk driving, fights, unprotected sex), and then have no memory of what they have done.  As previously discussed, intoxicated individuals due have access to previously formed memories, including morals, ethics, rules and laws.  However, they may lose the ability to base decisions on the previous stored information, or to recognize that their actions are immoral/illegal or right/wrong.  They may not fully comprehend that there may be consequences for their actions, or they just don’t care. 

A relationship between alcohol and aggression/violence has been well established.   Alcohol may not cause aggression, but it does increase the likelihood that individuals will act on their aggressive urges.

Some Alcohol Related Death Statistics

  • Accidental Deaths
  • 40% of motor vehicle fatalities (.15 BAC produces a 25-380x more likelihood to be involved in a fatal car accident)
  • 60% of boating fatalities
  • 70% of motorcycle fatalities
  • 41% of fatal falling injuries
  • 42% of death associated with fires
  • Homicide:  40-50% of those who commit homicide used alcohol prior to commission of the crime.
  • Suicide:  Alcoholism is a factor in about 30% of all completed suicides. 7% of individuals who are alcohol dependent will take their own lives.
  • Alcohol Poisoning:  Annually, 50 students from American universities and colleges die from alcohol poisoning, about one each weekend.
  • Alcohol is involved in 42% of the people treated in trauma centers. 


Legal Aspects of Blackouts

There is a debate related to whether an individual who commits a crime while in a blackout should be held as accountable for their actions as an individual who committed the same act while sober. 

The laws in most jurisdictions of the USA specifically disallow voluntary intoxication as a defense in criminal court.  However, involuntary intoxication (prescribed medications, being slipped something by someone else), often is a valid defense.

Victims who were in a blackout represent a difficult legal challenge.  For example, a woman engages in sexual activity, of which she has no memory the next day.  This may be extremely out of character for her.  She may assume that she was assaulted.  The accused male contends that she was a willing participant or even that she initiated the sexual activity.  It can be difficult, if not impossible, for another person to recognize that the individual is experiencing a blackout and will not recall these events later.  How did he know that she was in a blackout and not making sound decisions? This can seriously complicate a trial in which the victim just doesn’t remember what she did.  It is also possible that any memory of a drunken episode is colored by suggestion or outside information. Is the victim really a reliable witness?

Let’s go to our scenario.  Yes, this happens, even to law enforcement agents.  Look at the case NYPD Officers Kenneth Moreno and Franklin Mata.  They were acquitted of burglary and rape charges of a drunken fashion designer in her apartment.  They won their case, but lost their jobs/careers.  No matter what your personal opinion on the case was, three lives were changed for the worse and forever.

Do Blackouts Equate to Alcoholism?

Blackouts occur quite often among alcoholics. However, contrary to previous assumptions that blackouts only happen to alcoholics, it has been established that they frequently occur from social drinkers who drink too much, to the occasional binge drinker, or to an individual’s one and only experience with alcohol.  Black-outs are a consequence of acute intoxication regardless of age, gender, ethnicity, or if someone is alcohol dependent or not. 

If excessive drinking is tolerated anywhere, it is at college campuses.  A 2012 research study showed that over 50% of college students have had at least one blackout. 

Nonetheless, blackouts are a warning sign that an individual is drinking in a dangerous and a potentially fatal manner.  They should not be ignored.  A person who experiences blackouts may indeed have a serious problem with alcohol.  Blackouts are invariably frightening and are potentially tragic.  If someone suspects that they have a problem with alcohol, a screening test is recommended.  Alcohol abuse and dependence are problems that can be treated.