Alcohol (also known as ethanol) has a number of effects on health. Short-term effects of alcohol consumption include intoxication and dehydration. Long-term effects of alcohol include changes in the metabolism of the liver and brain, with increased risk of several types of cancer and alcohol use disorder. Alcohol intoxication affects the brain, causing slurred speech, clumsiness, and delayed reflexes. There is an increased risk of developing an alcohol use disorder for teenagers while their brain is still developing. Adolescents who drink have a higher probability of injury including death.

Light alcohol consumption was misclassified as possibly healthy in the past by several studies, but evidence shows that even minimal to light alcohol consumption can have negative effects on health, such as by increasing a person's risk of developing several cancers. A 2014 World Health Organization (WHO) report found that harmful alcohol consumption caused about 3.3 million deaths annually worldwide. Negative effects are related to the amount consumed with no safe lower limit seen. Some nations have introduced alcohol packaging warning messages that inform consumers about alcohol and cancer, as well as fetal alcohol syndrome. In modern medicine, the only possible beneficial uses of alcohol are as a topical disinfectant, temporary emergency cure for alcohol withdrawal syndrome, and, as long as kept in strict moderation, positive social effects outweighing harm to the body. Practically no authorities recommend starting drinking for any positive effects.

In January 2025, the surgeon general of the United States released an advisory describing a causal relationship between alcohol consumption and increased risk of seven different types of cancer, including colorectal cancer, liver cancer, and throat cancer. The advisory recommended updating the health warning label on alcohol-containing beverages in the United States to include a warning about the risk of cancer from consuming these beverages.

Short-term effects

The short-term effects of alcohol consumption range from a decrease in anxiety and motor skills at lower doses to unconsciousness, anterograde amnesia, and central nervous system depression at higher doses. Cell membranes are highly permeable to alcohol, so once alcohol is in the bloodstream it can diffuse into nearly every cell in the body.

The concentration of alcohol in blood is measured via blood alcohol content (BAC). The amount and circumstances of consumption play a large part in determining the extent of intoxication; for example, eating a heavy meal before alcohol consumption causes alcohol to absorb more slowly. Hydration also plays a role, especially in determining the extent of hangovers. After binge drinking, unconsciousness can occur and extreme levels of consumption can lead to alcohol poisoning and death (a concentration in the blood stream of 0.40% will kill half of those affected). Alcohol may also cause death indirectly, by asphyxiation from vomit.

Alcohol disrupts normal sleep patterns thereby reducing sleep quality and can greatly exacerbate sleep problems. During abstinence, residual disruptions in sleep regularity and sleep patterns are the greatest predictors of relapse.

Heavy alcohol consumption while in a hunger state can cause alcoholic ketoacidosis, a life-threatening metabolic derailment.

The median lethal dose of alcohol in test animals is a blood alcohol content of 0.45%. This is about six times the level of ordinary intoxication (0.08%), but vomiting or unconsciousness may occur much sooner in people who have a low tolerance for alcohol.Meyer, Jerold S. and Linda F. Quenzer. Psychopharmacology: Drugs, the Brain, and Behavior. Sinauer Associates, Inc.: Sunderland, Massachusetts. 2005. Page 228. The high tolerance of chronic heavy drinkers may allow some of them to remain conscious at levels above 0.40%, although serious health hazards are incurred at this level.

Alcohol also limits the production of vasopressin (antidiuretic hormone) from the hypothalamus and the secretion of this hormone from the posterior pituitary gland. This is what causes severe dehydration when alcohol is consumed in large amounts. It also causes a high concentration of water in the urine and vomit, and the intense thirst that goes along with a hangover.

Long-term effects

According to the World Health Organization's 2018 Global Status Report on Alcohol and Health, there are more than 3 million people who die from the harmful effects of alcohol each year, which amounts to more than 5% of the burden of disease worldwide. The US National Institutes of Health similarly estimates that 3.3 million deaths (5.9% of all deaths) were believed to be due to alcohol each year.

As per WHO June 2024 report on Alcohol, around 2.6 million deaths were caused by alcohol consumption in 2019 worldwide.

Guidelines in the US and the UK advise that if people choose to drink, they should drink modestly.

Even light and moderate alcohol consumption increases a person's cancer risk, especially the risk of developing squamous cell carcinoma of the esophagus, cancers of the mouth and tongue, liver cancer, and breast cancer. Using alcohol, especially together with tobacco, is a major risk factor for head and neck cancer. 72% of head and neck cancer cases are caused by using both alcohol and tobacco. This rises to 89% when looking specifically at laryngeal cancer.

A systematic analysis of data from the Global Burden of Disease Study, which was an observational study, found that long-term consumption of any amount of alcohol is associated with an increased risk of death in all people, and that even moderate consumption appears to be risky. Similar to prior analyses, it found an apparent benefit for older women in reducing the risks of death from ischemic heart disease and from diabetes mellitus, but unlike prior studies it found those risks cancelled by an apparent increased risk of death from breast cancer and other causes. A 2016 systematic review and meta-analysis found that moderate ethanol consumption brought no mortality benefit compared with lifetime abstention from ethanol consumption. Risk is greater in younger people due to heavy episodic drinking which may result in violence or accidents.

Long-term heavy use of alcohol damages nearly every organ and system in the body. Risks include alcohol use disorder, malnutrition, chronic pancreatitis, alcoholic liver disease (e.g., permanent liver scarring) and several types of cancer. In addition, damage to the central nervous system and peripheral nervous system (e.g., painful peripheral neuropathy) can occur from chronic alcohol misuse.

The developing adolescent brain is particularly vulnerable to the toxic effects of alcohol.

A systematic analysis found in 2022 that the level of alcohol consumption recommended by many existing guidelines is too high in particular for young people in all regions.

DNA damage

Acetaldehyde is produced when cells process ethanol. Acetaldehyde, is a DNA damaging metabolite that can interact with DNA to crosslink the two strands of the DNA duplex. The mechanisms the cells use for repairing these crosslinks are error prone, thus leading to mutations that in the long term can cause cancer.

Pregnancy and breastfeeding

Medical organizations strongly discourage drinking alcohol during pregnancy. Alcohol passes easily from the mother's bloodstream through the placenta and into the bloodstream of the fetus, which interferes with brain and organ development. Alcohol can affect the fetus at any stage during pregnancy, but the level of risk depends on the amount and frequency of alcohol consumed. Regular heavy drinking and heavy episodic drinking (also called binge drinking), entailing four or more standard alcoholic drinks (a pint of beer or 50 ml drink of a spirit such as whisky corresponds to about two units of alcohol) on any one occasion, pose the greatest risk for harm, but lesser amounts can cause problems as well. There is no known safe amount or safe time to drink during pregnancy, and the U.S. Centers for Disease Control and Prevention recommends complete abstinence for women who are pregnant, trying to become pregnant, or are sexually active and not using birth control.

Prenatal alcohol exposure can lead to fetal alcohol spectrum disorders (FASDs). The most severe form of FASD is fetal alcohol syndrome (FAS). Problems associated with FASD include abnormal facial development, low birth weight, stunted growth, small head size, delayed or uncoordinated motor skills, hearing or vision problems, learning disabilities, behavior problems, and inappropriate social skills compared to same-age peers. Those affected are more likely to have trouble in school, legal problems, participate in high-risk behaviors, and develop substance use disorders like excessive drinking themselves.

The UK National Health Service states that "an occasional drink is unlikely to harm" a breastfed baby, and recommends consumption of "no more than one or two units of alcohol once or twice a week" for breastfeeding mothers (where a pint of beer or 50 ml drink of a spirit such as whisky corresponds to about two units of alcohol). The NHS also recommends to wait for a couple of hours before breastfeeding or express the milk into a bottle before drinking. Researchers have shown that intoxicated breastfeeding reduces the average milk expression but poses no immediate threat to the child as the amount of transferred alcohol is insignificant.

Cardiovascular disease

In 2010, a systematic review reported that moderate consumption of alcohol does not cause harm to people with cardiovascular disease. However, the authors did not encourage people to start drinking alcohol in the hope of any benefit. In a 2018 study on 599,912 drinkers, a roughly linear association was found with alcohol consumption and a higher risk of stroke, coronary artery disease excluding myocardial infarction, heart failure, fatal hypertensive disease, and fatal aortic aneurysm, even for moderate drinkers. The American Heart Association states that people who are currently non-drinkers should not start drinking alcohol.

Insulin response Alcohol is known to potentiate the insulin response of the human body to glucose, which, in essence, "instructs" the body to convert consumed carbohydrates into fat and to suppress carbohydrate and fat oxidation. Ethanol is directly processed in the liver to acetyl CoA, the same intermediate product as in glucose metabolism. Because ethanol is mostly metabolized and consumed by the liver, chronic excessive use can lead to fatty liver. This leads to a chronic inflammation of the liver and eventually alcoholic liver disease.

Alcohol consumption can cause hypoglycemia in diabetics on certain medications, such as insulin or sulfonylurea, by blocking gluconeogenesis.

Alcoholic beverages show a lower satiety value per calorie.

Mental health Alcohol misuse often coincides with mental health conditions. Many individuals struggling with psychiatric disorders also experience problematic drinking behaviors.

Alcohol education

Alcohol education is the practice of disseminating information about the effects of alcohol on health, as well as society and the family unit. It was introduced into the public schools by temperance organizations such as the Woman's Christian Temperance Union in the late 19th century. Initially, alcohol education focused on how the consumption of alcoholic beverages affected society, as well as the family unit. In the 1930s, this came to also incorporate education pertaining to alcohol's effects on health. Organizations such as the National Institute on Alcohol Abuse and Alcoholism in the United States were founded to promulgate alcohol education alongside those of the temperance movement, such as the American Council on Alcohol Problems.

Alcohol expectations