Alcohol is one of the most widely consumed psychoactive substances on Earth, with roughly 400 million people worldwide living with an alcohol use disorder. Yet many of the basic facts about how alcohol works in the body, how it’s measured, and what it does to your health are poorly understood. Here are some of the most important things worth knowing.
What Counts as “One Drink”
In the United States, a standard drink contains 0.6 ounces (14 grams) of pure alcohol. That translates to 12 ounces of regular beer at 5% alcohol, 5 ounces of wine at 12%, or a 1.5-ounce shot of 80-proof liquor at 40%. These amounts look very different in a glass, but they deliver roughly the same amount of ethanol to your body. Most people underestimate how much they’re actually drinking, especially with wine or craft beer, where serving sizes and alcohol percentages often exceed these standards.
How Your Body Breaks Down Alcohol
Your liver does the heavy lifting. Two enzymes handle most of the work. The first converts alcohol into a compound called acetaldehyde, which is highly toxic and classified as a carcinogen. The second enzyme then converts acetaldehyde into acetate, which your body can break down into water and carbon dioxide for elimination. The entire process happens mainly in the liver, and acetaldehyde typically exists in your body only briefly before being processed further. But even that short window is enough to cause damage, particularly to liver cells.
Your body clears alcohol from your blood at a fairly fixed rate of about 0.019 g/dL per hour. That means if your blood alcohol concentration is 0.08% (the legal limit for driving in most U.S. states), it takes roughly four hours to fully metabolize. You can’t speed this up with coffee, cold showers, or food. Your liver simply works at its own pace.
What Alcohol Does to Your Brain
Alcohol affects nearly every chemical signaling system in the brain, but its most pronounced effect is on the balance between excitation and inhibition. When you drink, alcohol increases the activity of your brain’s main inhibitory system (the one that slows neural activity down) while simultaneously decreasing your brain’s main excitatory system (the one that speeds things up). This is why alcohol makes you feel relaxed, lowers your inhibitions, and slows your reaction time. It also boosts dopamine and your brain’s natural opioid-like chemicals, which is what makes drinking feel rewarding.
Over time, with heavy use, the brain adapts to this artificial calm by dialing up its excitatory systems and dialing down its inhibitory ones. Brain imaging studies consistently show that people with alcohol use disorder have lower levels of inhibitory brain chemicals in the cortex, especially during withdrawal. This rebound imbalance is why withdrawal can produce anxiety, tremors, and in severe cases, seizures.
Alcohol Is a Group 1 Carcinogen
The International Agency for Research on Cancer classified alcohol as a Group 1 carcinogen in 1987. That’s the same category as tobacco smoke and asbestos, meaning there is sufficient evidence that it causes cancer in humans. The specific cancers linked to alcohol consumption include cancers of the mouth and throat, voice box, esophagus, liver, breast, and colon/rectum.
The mechanism involves multiple pathways, but the most direct one is acetaldehyde, that toxic intermediate your liver produces while breaking alcohol down. Acetaldehyde can damage DNA and prevent cells from repairing that damage. During 2020 and 2021, more than 17,000 cancer deaths per year in the U.S. were attributable to excessive alcohol use.
It Makes You Dehydrated, and Here’s Why
Your body normally regulates water balance through a hormone called vasopressin, which tells your kidneys to hold onto water. Alcohol suppresses the release of this hormone by interfering with calcium signaling in the nerve endings that produce it. With less vasopressin circulating, your kidneys let more water pass through as urine. This is why you urinate more frequently when drinking and why you often wake up thirsty. The dehydration contributes to many classic hangover symptoms: headache, fatigue, and dizziness.
Alcohol Disrupts Sleep Architecture
A common misconception is that alcohol helps you sleep. It does make you fall asleep faster, and it initially increases deep, slow-wave sleep during the first half of the night. But it suppresses REM sleep, the phase most important for memory consolidation, emotional processing, and feeling rested. As your blood alcohol level drops in the second half of the night, REM sleep can rebound, often causing vivid dreams, restlessness, and frequent awakenings. The net result is that even if you slept a full eight hours after drinking, the quality of that sleep is significantly worse.
The Death Toll Is Higher Than Most People Think
Between 2020 and 2021, excessive alcohol use caused an average of 178,307 deaths per year in the United States. That figure represents a 29% increase from 2016 to 2017, when the average was about 138,000. The majority of these deaths, roughly 117,000 per year, came from chronic causes: conditions that develop over years of heavy drinking. These included heart disease and stroke (37,317 deaths per year), cancer (17,072), and liver, gallbladder, and pancreas diseases (12,719). Nearly 49,000 deaths came from conditions that are 100% attributable to alcohol, meaning they wouldn’t have occurred without it.
Acute causes accounted for another 61,000 deaths annually. Alcohol poisoning killed nearly 22,000 people per year, motor vehicle crashes involving alcohol killed about 15,000, and alcohol-related suicides accounted for roughly 9,800.
Global Scope of Alcohol Problems
According to the WHO’s 2024 global status report, around 400 million people aged 15 and older live with an alcohol use disorder, and approximately 209 million of those meet the criteria for alcohol dependence. While global deaths and disorder prevalence have declined somewhat since 2010, the overall health impact remains enormous. Alcohol contributes to more than 200 diseases and injury conditions worldwide, touching nearly every organ system in the body.