When you drink alcohol, your body breaks it down in a two-step process. Ethanol is first converted into acetaldehyde, a toxic compound classified as a carcinogen, and then into acetate, a relatively harmless substance your cells can use for energy. The entire process happens primarily in the liver, and your body can handle roughly one standard drink per hour.
The Two-Step Breakdown
Almost all alcohol metabolism follows the same sequence. In the first step, an enzyme called alcohol dehydrogenase converts ethanol into acetaldehyde. This is the dangerous intermediate, a compound that damages DNA, disrupts proteins, and is responsible for many of the harmful effects of drinking. Your body treats acetaldehyde as something to get rid of as quickly as possible.
In the second step, another enzyme (aldehyde dehydrogenase) converts acetaldehyde into acetate. Acetate is essentially harmless. It enters your bloodstream, travels to cells throughout your body, and gets fed into the same energy cycle your cells use to burn carbohydrates and fats. That cycle ultimately produces carbon dioxide, water, and a small amount of usable energy in the form of ATP. So the final breakdown products of alcohol are CO2 and water, just like most other fuel sources your body processes.
Why Acetaldehyde Is the Problem
The gap between step one and step two is where the damage happens. Acetaldehyde is a known carcinogen and mutagen. It interacts directly with DNA, causing point mutations, chromosomal damage, and the formation of abnormal chemical bonds between DNA and proteins. Any of these effects can activate cancer pathways or contribute to the kind of progressive liver injury that leads to scarring (fibrosis) and eventually cirrhosis.
Acetaldehyde also latches onto proteins and interferes with their function. When it binds to structural proteins inside liver cells, it disrupts the internal architecture of those cells. When it accumulates on collagen, the connective tissue protein, it promotes scar tissue formation. It even stimulates liver cells to produce more collagen than they normally would, accelerating the scarring process. This is a central mechanism behind alcohol-related liver disease.
Acetaldehyde is also widely considered a major contributor to hangovers. The faster your body clears it, the less damage it does and the better you feel. Some people, particularly those of East Asian descent, carry genetic variants that slow down acetaldehyde processing, which is why they often experience facial flushing, nausea, and rapid heartbeat after even small amounts of alcohol.
How Fast Your Body Clears Alcohol
For a person weighing about 154 pounds (70 kg), the liver can process roughly 7 grams of alcohol per hour. That translates to about one standard drink per hour, whether it’s a 12-ounce beer, a 5-ounce glass of wine, or a 1.5-ounce shot of liquor. Drink faster than that and alcohol accumulates in your bloodstream, which is how blood alcohol concentration rises.
There is no way to speed this up. Coffee, cold showers, and food don’t accelerate the enzymatic process. Your liver works at a fixed pace determined largely by your genetics, body size, and drinking history.
The Backup Pathway for Heavy Drinking
The main enzyme system handles about 90% of alcohol metabolism under normal conditions. But your body has a backup: a secondary system involving an enzyme called CYP2E1. Under normal circumstances, this backup pathway is inefficient and plays a minor role, processing roughly 10% of the alcohol you consume.
That changes with heavy drinking. When blood alcohol levels are high, CYP2E1 ramps up and takes on a larger share of the work. Chronic drinkers and binge drinkers actually induce higher levels of this enzyme over time, which is one reason heavy drinkers develop a higher tolerance for alcohol. Their bodies literally become more efficient at metabolizing it. The end product is the same, acetaldehyde, but this secondary pathway also generates harmful molecules called free radicals that cause additional oxidative damage to liver cells.
What Happens Outside the Liver
The liver does the vast majority of the work, but alcohol metabolism also occurs in smaller amounts in other organs, including the pancreas and the brain. In the brain, the enzyme catalase and CYP2E1 can both convert ethanol into acetaldehyde locally. This means acetaldehyde can be produced directly in brain tissue, where it may contribute to alcohol’s neurological effects and long-term brain damage, rather than only being a problem in the liver.
A small fraction of alcohol never gets metabolized at all. About 1 to 2% of the alcohol you drink is excreted unchanged through your breath, sweat, and urine. This unmetabolized portion is what breathalyzers detect, and it’s why you can sometimes smell alcohol on someone’s breath hours after they’ve been drinking.
How Acetate Becomes Energy
Once acetaldehyde is safely converted to acetate, the story becomes much less dramatic. Acetate leaves the liver, enters the bloodstream, and is taken up by cells throughout the body. Inside those cells, it gets converted into a molecule called acetyl-CoA, which feeds into the citric acid cycle, the same energy-producing process that handles fuel from carbohydrates and fats. The cycle strips away carbon atoms and releases them as carbon dioxide (which you exhale) and water, generating usable energy along the way.
This is why alcohol contains calories, about 7 per gram, which sits between carbohydrates (4 per gram) and fat (9 per gram). Your body genuinely extracts energy from alcohol. But there’s a catch: while your liver is busy processing ethanol, it deprioritizes other metabolic tasks like burning fat and maintaining blood sugar. This is one reason heavy drinking is linked to weight gain and fatty liver, even before serious liver disease develops. Your body is so focused on clearing the toxic intermediate that everything else gets pushed to the back of the line.