Alcohol-Induced Blackouts

Key takeaway

NIAAA says an alcohol blackout is a memory gap for events while intoxicated, because alcohol blocks memory consolidation in the hippocampus. The person can still be awake. Passing out is loss of consciousness, not the same event. Fast drinking, an empty stomach, or a binge makes a blackout more likely. Even one is a reason to talk with a clinician.

Last updated: Mon Oct 05 2026 00:00:00 GMT+0000 (Coordinated Universal Time)

You woke up and a stretch of the night is missing. NIAAA's fact sheet, updated in June 2025, defines alcohol-induced blackouts as gaps in memory for events that happened while intoxicated. The gaps occur when someone drinks enough alcohol to temporarily block the transfer of memories from short-term storage into long-term storage. That transfer is called memory consolidation. The brain area NIAAA names is the hippocampus.

The sheet says this can happen to anyone who drinks, at any age, and at any level of experience. It is not a badge of a hard night, and it is not proof by itself of alcohol use disorder. It is a harm. The same sheet says blackouts carry a sharply higher risk of injuries and other harms.

The drinking pattern that often produces a blackout is defined on the binge drinking guide. Consent when judgment and memory fail is the subject of the sex and sobriety guide. How much is too much on ordinary days is the question on the gray-area drinking guide. Those pages mention blackouts. The two types are explained here.

If someone will not wake, is having a seizure, is breathing slowly, or may be choking, call 911. For a mental health crisis, call or text 988.

Two kinds of missing memory

NIAAA divides blackouts by how much memory is lost.

The most common type is a fragmentary blackout. Memories of the events are spotty. Islands of memory sit between missing periods. People sometimes call this a grayout or a brownout. Pieces may return later. That return does not make the gap harmless, and it does not fill in what is still missing.

The severe form is an en bloc blackout. Amnesia is complete and often lasts hours. Memories of the events do not form, and they typically cannot be recovered. NIAAA's image is that it is as if the events never occurred. Friends' stories, photos, and a phone log are other people's records. They are not a memory the hippocampus stored.

Neither type is a personality. Both are alcohol effects. Questions you ask the next day, including what you said yes to, belong with the fact that memory was not being written down.

When the rise is fast

NIAAA says blackouts are more likely when blood alcohol concentration rises rapidly. The situations it names are drinking on an empty stomach, drinking quickly, and binge drinking. For a typical adult, the binge guide defines a pattern that brings blood alcohol to 0.08 percent, often four drinks for women or five for men in about two hours. The blackout sheet does not add a second, higher number that "starts" a blackout. Do not invent a personal threshold the fact sheet does not print.

Certain medicines make a blackout more likely. NIAAA names medicines for sleep and for anxiety. Its overdose fact sheet is more specific about the combination: alcohol plus opioids, or plus sedatives such as benzodiazepines and some sleep medicines, can suppress breathing, and even moderate amounts of alcohol can be enough for an overdose when those drugs are also present. Over-the-counter antihistamines can be dangerous with alcohol too. What naloxone reverses in an opioid emergency is on the naloxone guide. Naloxone does not reverse an alcohol blackout.

NIAAA also explains a sex difference in averages, not in worth. Females, on average, weigh less than males and, pound for pound, have less water in their bodies. They tend to reach higher peak blood alcohol levels than males with each drink, and they reach those peaks more quickly. NIAAA says this helps explain why females appear to be at higher risk for blackouts. An average is not a measurement of the person in front of you.

At those high levels, memory is not the only function that fails. Impulse control, attention, judgment, and decision-making are significantly impaired. A person can hold a conversation, send a text, or agree to a ride and still not be making an intact decision. The sex and sobriety page is where consent is spelled out. Being on your feet does not turn a blackout into agreement.

Awake is not the same as safe

NIAAA draws a line between a blackout and passing out. Passing out means falling asleep or losing consciousness from too much alcohol. During a blackout, the person is still awake. The brain is not creating new memories. Depending on the amount, a blackout can turn into passing out.

That is why "they were talking, so they were fine" is a weak safety plan. NIAAA's overdose page says that as blood alcohol rises, blackouts, loss of consciousness, and death can all occur. Blood alcohol can keep rising after the person stops drinking or becomes unconscious, because alcohol still in the stomach and intestine continues to enter the blood. Assuming an unconscious person will sleep it off is dangerous. A missing gag reflex can let them choke on vomit. NIAAA says an overdose can cause permanent brain damage or death.

Get emergency help. Do not wait until every sign is present. NIAAA's critical signs include mental confusion or stupor, trouble staying conscious or an inability to wake, vomiting, seizures, fewer than eight breaths a minute, gaps of 10 seconds or more between breaths, a slow heart rate, clammy skin, dulled responses such as no gag reflex, and very low body temperature with bluish or pale skin. Cold showers, hot coffee, and walking someone around do not reverse an overdose and can make it worse. Do not leave the person alone. Keep them on the ground, sitting or partly upright, not in a chair. If they are vomiting, have them lean forward. If they are unconscious or lying down, roll them onto one side with an ear toward the ground.

Tell responders what was drunk, what other drugs you know about, and any medicines, allergies, or conditions you know. A next-day headache, thirst, and nausea are a different NIAAA fact sheet, covered on the hangover guide. Those symptoms are not the overdose signs above.

What one gap means

NIAAA says blackouts are not necessarily alcohol use disorder. It also says even one is a reason for concern, and a reason to look at your drinking and talk with a health care provider. Questions about blackouts at an ordinary medical visit can serve as a simple screen for other alcohol-related harm. A screen is not a sentence.

In research among college students and other young adults, NIAAA says the frequency of blackouts predicts other consequences: missing work or school, a lower grade point average, injury, an emergency department visit, arrest, or other negative outcomes. Campus context is on the college recovery guide. A single blackout at 40 is not the same research event as a pattern at 19. The fact sheet's advice is the same either way: talk with a clinician.

Blackouts are among the problems a clinician may ask about when assessing alcohol use disorder, which the high-functioning guide lists. Continuing to drink despite blackouts is one of those questions. It belongs in a clinical visit.

If the drinking has been heavy for a long time, do not answer the blackout by quitting on your own that morning. A fast stop can be medically dangerous. The medical risk is explained on the withdrawal guide. Where that care should happen is the question on the home versus medical detox guide. Neither one offers a drink schedule.

FindTreatment.gov lists programs. Call or text (800) 653-9376 if you want help finding an assessment.

Additional Resources

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Common Questions

Is a blackout the same as passing out?

No. NIAAA's 2025 fact sheet says that during a blackout the person is still awake, but the brain is not creating new memories. Passing out means falling asleep or losing consciousness from drinking too much. A person can move from a blackout into passing out, depending on how much they drank. Someone who will not wake is an emergency. Call 911.

What is the difference between a fragmentary blackout and an en bloc blackout?

NIAAA says the fragmentary type is the most common. Memories are spotty, with islands of recall and missing stretches between them. People also call that a grayout or a brownout. An en bloc blackout is complete amnesia, often for hours. Those memories do not form and typically cannot be recovered. Neither type is a diagnosis by itself.

Does one blackout mean I have alcohol use disorder?

Not necessarily. NIAAA says blackouts are not necessarily a sign of alcohol use disorder, and that even one is a reason for concern. It says the person should consider their relationship with alcohol and talk with a health care provider. Research it summarizes, in college students and other young adults, found that more frequent blackouts predicted other harms, including missed school or work, injury, emergency care, and arrest. Frequency is a warning. It is not a label you can apply to yourself from a fact sheet.

Why are some people more likely to black out?

NIAAA says blackouts are more likely when someone drinks on an empty stomach, drinks quickly, or binge drinks, because blood alcohol can rise fast. Certain sleep and anxiety medicines also raise the chance. It says females, on average, reach higher peak blood alcohol levels than males with each drink, and reach those peaks faster, because of average differences in weight and body water. Those are group patterns. They do not measure one person's night.

What if I cannot remember whether I agreed to something?

A gap in memory is not consent. Impulse control, attention, judgment, and decision-making are significantly impaired at the high blood alcohol levels NIAAA ties to blackouts. The sex and sobriety guide is the page for consent, including when someone is too intoxicated to agree. If you may have been assaulted, call 911. Friends' stories do not fill in a night the brain did not store.