Skip to Content



Gerald F. O’Malley

, DO, Grand Strand Regional Medical Center;

Rika O’Malley

, MD, Albert Einstein Medical Center

Last full review/revision Jun 2020| Content last modified Jun 2020

Alcohol (ethanol) is a depressant. Consuming large amounts rapidly or regularly can cause health problems, including organ damage, coma, and death.

  • Genetics and personal characteristics may play a part in the development of alcohol-related disorders.
  • Drinking too much alcohol may make people sleepy or aggressive, impair coordination and mental function, and interfere with work, family relations, and other activities.
  • Drinking too much alcohol for a long time can make people dependent on alcohol and damage the liver, brain, and heart.
  • Doctors may use questionnaires or determine the blood alcohol level to help identify people with an alcohol-related disorder.
  • Immediate treatment for overdose may include assistance with breathing, fluids, thiamin and sometimes other vitamins (to correct chronic alcohol-related deficiencies), and, for withdrawal, benzodiazepines.
  • Detoxification and rehabilitation programs can help people with severe alcohol-related disorders.

(See also Drug Use and Abuse.)

About half of adults in the United States currently drink alcohol, 20% are former drinkers, and 30 to 35% are lifetime abstainers. Drinking large amounts of alcohol (more than 2 to 6 drinks per day) for extended periods can damage a number of organs, especially the liver, heart, and brain. However, drinking a moderate amount of alcohol may reduce the risk of death from heart and blood vessel (cardiovascular) disorders. Nonetheless, drinking alcohol for this purpose is not recommended, especially when other safer, more effective preventive measures are available.

Alcohol-related disorders

Most people do not consume enough alcohol or consume it often enough to impair their health or interfere with their activities. However, 7 to 10% of adults in the United States have a problem with alcohol use (alcohol use disorder, also known as alcoholism). Men are 2 to 4 times more likely than women to develop alcohol use disorder. Alcohol and other substance use disorders involve people continuing to use a substance even though they have problems caused by its use.

Classifying Alcohol-Related Disorders



At-risk drinking

Defined by the amount and frequency of drinking:

  • More than 14 drinks* a week or 4 drinks per occasion for men
  • More than 7 drinks a week or 3 drinks per occasion for women

Binge drinking

  • 5 or more drinks per occasion for men
  • 4 or more drinks per occasion for women
  • Can go on for many days, followed by no or little alcohol for several days
  • A particular problem in younger people

Alcohol use disorder

  • Prevents people from fulfilling their obligations
  • Is done in physically dangerous situations (such as driving)
  • Results in legal, social, or interpersonal problems
  • More and more alcohol needed to produce the same effects (tolerance)
  • Stopping drinking results in unpleasant, sometimes painful, physical symptoms (withdrawal)
  • Drinking more than intended
  • Reducing use desired but not possible
  • Spending a lot of time getting or drinking alcohol or recovering from its effects
  • Missing important events or activities (such as work, a wedding, or a graduation) because of drinking
  • Continuing to drink even though drinking is causing physical or psychologic problems
  • Craving alcohol

* One drink is equivalent to 12 ounces of beer, 5 ounces of wine, or 1½ ounces of liquor, such as whiskey.

Did You Know...

  • Drinking very large amounts of alcohol can quickly cause death.

Alcohol use can lead to many destructive behaviors and effects:

  • Drunk driving
  • Physical injury from falls, fights, or motor vehicle accidents
  • Violence, including domestic violence

Drunkenness may disrupt family and social relationships. The divorce rate is 50% higher when one spouse is a heavy drinker. Extreme absenteeism from work can lead to unemployment.

Special populations

Very young children who drink alcohol (typically accidentally) are at significant risk of very low blood sugar and coma.

Women may be more sensitive to the effects of alcohol than men, even on a per-weight basis.

Older people may be more sensitive to the effects of alcohol than younger adults.

Women who drink during pregnancy have an increased risk of giving birth to a baby with fetal alcohol syndrome.

Although sensitivity to the effects of alcohol may vary with age, people of all ages are susceptible to alcohol use disorders. Increasingly, drug and substance use and abuse among adolescents has been linked with especially disastrous consequences. Those who start drinking at an early age (particularly the preteen years) are much more likely to become dependent on alcohol as adults.


Alcohol use disorder involves heredity to some extent. Blood relatives of people with alcohol use disorder are more likely to have alcohol use disorder than people in the general population, and alcohol use disorder is more likely to develop in biologic children of people with alcohol use disorder than in adopted children.

Some research suggests that people at risk of alcohol use disorder are less easily intoxicated than people who are not problem drinkers. That is, their brains are less sensitive to the effects of alcohol. Blood relatives of people with alcohol use disorder may have this trait.

Certain background and personality traits may predispose people to alcohol use disorder. People with alcohol use disorder frequently come from broken homes, and relationships with their parents are often disturbed. They tend to feel isolated, lonely, shy, depressed, or hostile. They may act self-destructively and may be sexually immature. Whether such traits are the cause of alcohol use disorder or the result is not certain.


Alcohol causes three basic types of problems:

  • Those that occur immediately when people drink too much at a particular time (intoxication and overdose)
  • Those that occur over a long period of time when people regularly consume excessive amounts
  • Those that occur when heavy, long-term use is stopped suddenly (withdrawal)

Immediate effects

Alcohol has almost immediate effects because it is absorbed faster than it is processed (metabolized) and eliminated from the body. As a result, alcohol levels in the blood rise rapidly. Effects can occur within a few minutes of drinking.

Effects vary greatly from person to person. For example, people who drink regularly (2 or more drinks per day) are less affected by a given amount of alcohol than those who normally do not drink or drink only socially, a phenomenon termed tolerance. People who have developed tolerance to alcohol may also be tolerant to other drugs that slow brain function, such as barbiturates and benzodiazepines.

Effects vary depending on the level of alcohol in the bloodstream, which is usually expressed in the United States in terms of milligrams per deciliter (1/10 liter of blood), abbreviated mg/dL and in other parts of the world as millimoles per liter abbreviated mmol/L. Actual blood levels required to produce given symptoms vary greatly with tolerance, but in typical users who have not developed tolerance, the following symptoms are typical:

  • 20 to 50 mg/dL (4.3 to 10.9 mmol/L): Tranquility, mild drowsiness, some decrease in fine motor coordination, and some impairment of driving ability
  • 50 to 100 mg/dL (10.9 to 21.7 mmol/L): Impaired judgment and a further decrease in coordination
  • 100 to 150 mg/dL (21.7 to 32.6 mmol/L): Unsteady gait, slurred speech, loss of behavioral inhibitions, and memory impairment
  • 150 to 300 mg/dL (32.6 to 65.1 mmol/L): Delirium and lethargy (likely)
  • 300 to 400 mg/dL (65.1 to 86.8 mmol/L): Often unconsciousness
  • ≥ 400 mg/dL (≥86.8 mmol/L): Possibly fatal

Vomiting is common with moderate to severe alcohol intoxication. Because people may be very drowsy, vomited material may enter the lungs (be aspirated), sometimes leading to pneumonia and death.

In the United States, all states define driving with a blood alcohol content (BAC) at or above 80 mg/dL (17.4 mmol/L; 0.08%) as a crime, but specific state laws and penalties vary.


In people who do not drink regularly, a blood alcohol level of 300 to 400 mg/dL (65.1 to 86.8 mmol/L) often causes unconsciousness, and a blood alcohol level of ≥ 400 mg/dL (≥ 86.8 mmol/L) can be fatal. Death can occur due to impaired breathing or abnormal heart rhythms (arrhythmia), especially when large quantities are drunk rapidly. Low blood pressure and low blood sugar levels can be caused by drinking large amounts of alcohol.

The effects of a particular blood level differ in chronic drinkers. Many seem unaffected and appear to function normally with relatively high levels, such as 300 to 400 mg/dL (65.1 to 86.8 mmol/L).

Alcohol, even in moderate doses, interferes with short-term memory formation which may cause blackouts. The intoxicated individual may seem gregarious and loquacious but will have limited memory of the blackout period.

Long-term effects

Prolonged use of excessive amounts of alcohol damages many organs of the body, particularly the liver (alcohol-related liver disease). Because people may not eat an adequate diet, they may also develop severe vitamin and other nutritional deficiencies.

Effects of Prolonged Alcohol Use

Type of Problem



Low folate (folic acid) levels

Anemia (fatigue, weakness, and light-headedness)

Birth defects

Low thiamin levels

Neurologic damage, dementia, difficulty walking and controlling eye movements

Low iron levels


Low niacin levels

Pellagra (skin damage, diarrhea, and depression)




Inflammation (esophagitis)



Inflammation (gastritis)



A bleeding tendency (coagulopathy)


Fatty liver

Inflammation (hepatitis)

Severe scarring (cirrhosis)


Inflammation (pancreatitis)

Low blood sugar levels (hypoglycemia)



Disturbance of the heart’s rhythm (arrhythmia)

Heart failure, cardiomyopathy

Blood vessels


High blood pressure





Poor short-term memory (poor recall of recent events)

Psychosis (loss of contact with reality)

Reduced coordination


Deterioration of nerves in the arms and legs that control movements (reduced ability to walk) and sensation.


Reproductive organs

Decreased sex drive

In men, enlarged breasts, smooth skin, and shrinking of the testes

Alcohol-related liver disease includes liver inflammation (hepatitis), fatty liver, and liver scarring (cirrhosis). An alcohol-damaged liver is less able to rid the body of toxic waste products, which can cause brain dysfunction (hepatic encephalopathy). People developing hepatic encephalopathy become dull, sleepy, stuporous, and confused and may lapse into a coma. Hepatic coma is life threatening and needs to be treated immediately.

Usually, people with liver failure also have liver flap (asterixis): When the arms and hands are outstretched, the hands suddenly drop, then resume their original position. Liver flap resembles but is not a tremor.

Cirrhosis of the liver causes pressure to build up in the blood vessels around the liver (portal hypertension). Built up pressure in these blood vessels can cause swelling of blood vessels in the stomach and esophagus (varices.) These swollen vessels can rupture and bleed heavily, causing people to vomit blood. This bleeding is a particular problem because the damaged liver does not produce enough of the substances that make blood clot.

Inflammation of the pancreas (pancreatitis) can be caused by excessive alcohol use. People develop severe abdominal pain with vomiting.

Damage to the nerves and parts of the brain also can be caused by excessive alcohol use. When the nerves to the arms and legs (peripheral nerves) are affected, people may have loss of sensation or feel pins and needles in their hands and feet. People may develop a chronic tremor. Damage to the part of the brain that coordinates movement (cerebellum) can lead to poorly controlled movement of the arms and legs and affect balance. Heavy long-term alcohol use can result in irreversible brain damage and psychosis. It can also damage the lining (myelin sheath) of nerves in the brain, resulting in a rare disorder called Marchiafava-Bignami disease. People with this disorder become agitated, confused, and demented. Some develop seizures and go into a coma before dying.

A severe deficiency of thiamin, a B vitamin, can be caused by heavy long-term use of alcohol. This deficiency can lead to Wernicke encephalopathy (a condition characterized by confusion, inability to coordinate while walking, or difficulty coordinating movement of the eyes), which, if not promptly treated, may result in Korsakoff syndrome, coma, or even death.

Existing depression may be worsened by drinking alcohol, and people with alcohol use disorder are more likely to become depressed than people who are not problem drinkers. Because alcohol-related disorders, especially binge drinking, often causes deep feelings of remorse during dry periods, people with alcohol use disorder are prone to suicide even when they are not drinking.

Severe problems in the developing fetus, including low birth weight, short body length, small head size, heart damage, muscle damage, and low intelligence or intellectual disability, can be caused by alcohol use in pregnant women. These effects are called the fetal alcohol syndrome. Avoidance of alcohol is therefore recommended during pregnancy.

Withdrawal symptoms

If people who drink continually for a period of time suddenly stop drinking, withdrawal symptoms are likely. For example, withdrawal can occur during hospitalization (for example, for elective surgery) because drinkers are unable to obtain alcohol.

Withdrawal symptoms vary from mild to severe. Severe untreated alcohol withdrawal can be fatal.

Mild to moderate withdrawal usually begins within 6 hours after drinking stops. Mild symptoms include tremor, headache, weakness, sweating, and nausea. Some people have seizures (called alcohol-related epilepsy or rum fits).

Alcohol-related hallucinosis may occur in heavy drinkers who stop drinking. They hear voices that seem accusatory and threatening, causing apprehension and terror. Alcohol-related hallucinosis may last for days and can be controlled with antipsychotic drugs, such as chlorpromazine or thioridazine.

Delirium tremens (DTs) is the most serious group of withdrawal symptoms. Usually, delirium tremens does not begin immediately. Rather, it appears about 48 to 72 hours after the drinking stops. People are initially anxious. Later, they become increasingly confused, do not sleep well, have frightening nightmares, sweat excessively, and become very depressed. The pulse rate speeds up and the blood pressure rises. Fever typically develops. The episode may escalate to include fleeting hallucinations, illusions that arouse fear and restlessness, and disorientation with visual hallucinations that may be terrifying. Objects seen in dim light may be particularly terrifying, and the people become extremely confused. Their balance is impaired, sometimes making them think the floor is moving, the walls are falling, or the room is rotating. As the delirium progresses, a persistent tremor develops in the hands and sometimes extends to the head and body. Most people become severely uncoordinated. Delirium tremens can be fatal, particularly when untreated.


  • Self-reports of alcohol intoxication
  • Blood tests
  • Screening questionnaires

Acute alcohol intoxication is usually apparent based on what people or their friends tell the doctor and on results of the physical examination. If it is not clear why a person is acting abnormally, doctors may do tests to rule out other possible causes of symptoms, such as low blood sugar or head injury.

Tests may include blood tests to determine the amount of alcohol in the blood and the blood sugar level, urine tests for certain toxic substances, and computed tomography (CT) of the head. Doctors do not assume that simply because people have alcohol on their breath that nothing else could be wrong.

For legal purposes (for example, when people are in vehicle crashes or are acting abnormally at work), alcohol levels can be measured in the blood or estimated by measuring the amount in a sample of exhaled breath.

In people with long-term alcohol use, blood tests may be done to check for abnormalities in liver function and evidence of other organ damage. If symptoms are very severe, an imaging test such as CT may be done to rule out a brain injury or infection.

Screening for alcohol use disorder

Some people may not know that their amount of drinking could be a problem. Others know but do not want to admit that they have an alcohol problem. Therefore, health care practitioners do not wait for people to ask for help. They may suspect alcohol use disorder in people whose behavior changes inexplicably or whose behavior becomes self-destructive. They may also suspect alcohol use disorder when medical problems, such as high blood pressure or stomach inflammation (gastritis), do not respond to usual treatment.

Many practitioners periodically screen people for alcohol-related problems by asking about their use of alcohol. Questions may include the following:

  • On average, how many days per week do you drink alcohol?
  • On a typical day when you drink, how many drinks do you have?
  • What is the maximum number of drinks you had on any given occasion in the past month?

If doctors suspect alcohol use disorder, they may ask more specific questions about consequences of drinking, such as the following:

  • Have you ever felt you should cut down on your drinking?
  • Does criticism of your drinking annoy you?
  • Have you ever felt guilty about drinking?
  • Have you ever had an “eye opener” (a drink first thing in the morning) to steady your nerves or to get rid of a hangover?

Two or more “yes” answers to these questions indicate a probable alcohol use disorder.


Treatment may involve the following situations:

  • People are brought in because they have symptoms related to high blood alcohol levels.
  • People come because they have intolerable withdrawal symptoms. However, people who develop alcohol withdrawal symptoms usually treat themselves by drinking.
  • People come because they do not want to continue drinking.

Emergency treatment

Emergency treatment is needed when very large amounts of alcohol consumed or alcohol withdrawal causes moderate to severe symptoms.

There is no specific antidote for acute intoxication:

  • Coffee and other home remedies do not reverse the effects of alcohol.
  • If people are in a coma or their breathing is suppressed, they may need to have a tube inserted in their airway to keep them from choking on vomit and secretions and to help them breathe.
  • Fluids are given intravenously if needed to prevent or treat dehydration or low blood pressure.
  • Suspected chronic alcohol drinkers are given thiamin to prevent Wernicke encephalopathy. Often, doctors also add magnesium (which helps the body process thiamin) and multivitamins (for possible vitamin deficiencies) to the fluids.

Did You Know...

  • There is no specific antidote for acute alcohol intoxication: coffee, fluids, vitamins, or other remedies do not help people become sober.

For alcohol withdrawal symptoms, doctors often prescribe a benzodiazepine (a mild sedative) for a few days. It reduces agitation and helps prevent some withdrawal symptoms, seizures, and delirium tremens. Because people can become dependent on benzodiazepines, these drugs are used for only a short time. Antipsychotic drugs are sometimes given to people with alcohol-related hallucinosis.

Delirium tremens can be life threatening and is treated aggressively to control the high fever and severe agitation. People are treated in an intensive care unit if possible. Treatment usually includes the following:

  • High doses of benzodiazepines and barbiturates, given intravenously
  • High doses of vitamins (especially thiamin)
  • Fluids given intravenously
  • External cooling measures such as cooling blanket
  • Drugs that control heart rate and blood pressure
  • Treatment of complications (such as pancreatitis, pneumonia, and seizures)

With such treatment, delirium tremens usually begins to clear within 12 to 24 hours of its beginning, but severe cases may last for 5 to 7 days. Most people do not remember events during severe withdrawal after it resolves.

After any urgent medical problems are resolved, further treatment depends on the severity of alcohol use and other medical and psychiatric conditions of the patient. If people have not become dependent on alcohol, doctors may discuss the serious consequences of alcohol use with them, recommend ways to reduce or stop their drinking, and schedule follow-up visits to check on how well they are doing.

For people with more severe alcohol use, particularly those who have coexisting medical and psychiatric conditions, a detoxification and rehabilitation program may be recommended.

Detoxification and rehabilitation

In the first phase, alcohol is completely withdrawn, and any withdrawal symptoms are treated. Then people with alcohol use disorder have to learn ways to modify their behavior. Without help, most problem drinkers relapse within a few days or weeks. Rehabilitation programs, which combine psychotherapy with medical supervision, can help. People are warned about how difficult stopping is. They are also taught ways to enhance the motivation to stop and to avoid situations that are likely to trigger drinking. Treatment is tailored to the individual. These programs also enlist the support of family members and friends. Self-help groups, such as Alcoholics Anonymous, can also help.

Sometimes certain drugs (disulfiram, naltrexone, acamprosate, and clonidine) can help people with alcohol use disorder avoid drinking alcohol. However, drugs can typically help only if people are motivated and cooperative and if the drugs are used as part of an ongoing intensive counseling regimen. Results vary.

Disulfiram deters drinking because it interferes with alcohol metabolism, causing acetaldehyde (a substance that results from the breakdown of alcohol) to build up in the bloodstream. Acetaldehyde makes people feel ill. Within 5 to 15 minutes after people who took disulfiram drink alcohol, the buildup of acetaldehyde causes

  • Facial flushing
  • A throbbing headache
  • A rapid heart rate
  • Rapid breathing
  • Sweating

Nausea and vomiting may follow 30 to 60 minutes later. These uncomfortable and potentially dangerous reactions last 1 to 3 hours.

The discomfort from drinking alcohol after taking disulfiram is so intense that few people risk drinking alcohol—even the small amount in some over-the-counter cough and cold preparations or some foods.

Disulfiram must be taken every day in order for it to be effective in stopping drinking.

The following people should not use disulfiram:

  • Pregnant women
  • People who have a serious illness such as heart failure
  • Older people

Naltrexone alters the effects of alcohol on certain chemicals made by the brain (endorphins), which may be associated with alcohol craving and consumption. This drug is effective in most people who take it consistently. A long-acting form can be given by injection once a month. Naltrexone, unlike disulfiram, does not make people sick. Thus, people taking naltrexone can continue to drink. Naltrexone should not be taken by people who have hepatitis or certain other liver disorders.

Clonidine is a drug that affects certain parts of the brain and is typically used for high blood pressure but can help relieve some of the effects of alcohol withdrawal.

Alcoholics Anonymous: A Path to Recovery

No approach has benefited so many people with alcohol use disorder as effectively as Alcoholics Anonymous (AA). AA is an international fellowship of people who want to stop drinking. There are no dues or fees. The program operates on the basis of the “Twelve Steps,” which offers problem drinkers a new way of living without alcohol. Members of the fellowship typically work with a sponsor—a fellow member who is abstaining from alcohol use—who offers guidance and support. AA operates within a spiritual context but is not affiliated with any specific ideology or religious doctrine. However, alternative organizations, such as LifeRing Recovery (Secular Organizations for Sobriety), exist for those seeking a more secular approach.

AA helps its members in other ways as well. It provides a place where people recovering can socialize away from alcohol and with friends who do not drink and who are always available for support when the urge to start drinking again becomes strong. In meetings, people with alcohol use disorder hear other people relate—to the entire group—how they are struggling every day to avoid taking a drink. By providing a means to help others, AA builds self-esteem and confidence formerly found only in drinking alcohol. Most metropolitan areas have many AA meetings available day and night, 7 days a week. People with alcohol use disorder are encouraged to try several different meetings and to attend those at which they feel most comfortable.

More Information about Alcohol

  • Alcoholics Anonymous
  • Al-Anon Family Groups
  • LifeRing
  • National Institute on Alcohol Abuse and Alcoholism

Drugs Mentioned In This Article

Generic Name Select Brand Names
chlorpromazine No US brand name
acamprosate CAMPRAL
naltrexone REVIA
disulfiram ANTABUSE
clonidine CATAPRES

Copyright © 2022 Merck & Co., Inc., known as MSD outside of the US, Kenilworth, New Jersey, USA. All rights reserved. Merck Manual Disclaimer