Metabolizing alcohol is the process your body uses to break down ethanol into simpler, harmless compounds that can be eliminated. Most of this work happens in the liver, where enzymes convert alcohol first into a toxic intermediate called acetaldehyde, then into acetate, and finally into water and carbon dioxide. The average person clears alcohol at a rate of about 0.015 to 0.020 blood alcohol concentration (BAC) per hour, which roughly translates to one standard drink every 60 to 90 minutes.
The Two-Step Breakdown
Alcohol metabolism is essentially a two-step chemical reaction. In the first step, an enzyme called alcohol dehydrogenase (ADH) strips electrons from ethanol and converts it into acetaldehyde. Acetaldehyde is a highly reactive, toxic compound and a known carcinogen. Fortunately, under normal circumstances it doesn’t stick around long.
In the second step, another enzyme called aldehyde dehydrogenase (ALDH) quickly converts acetaldehyde into acetate, a much less harmful substance. Acetate then leaves the liver and is broken down into water and carbon dioxide by tissues throughout the rest of the body. Both steps happen primarily inside liver cells, though the final cleanup of acetate occurs elsewhere.
What Happens During Heavy Drinking
The standard ADH pathway handles moderate amounts of alcohol efficiently, but it has limits. When someone drinks heavily or chronically, the liver activates a backup system sometimes called the microsomal ethanol-oxidizing system (MEOS). This system relies on a different enzyme, CYP2E1, which also converts ethanol into acetaldehyde but comes with a significant downside: it generates large quantities of unstable molecules called free radicals.
Those free radicals deplete the liver’s built-in antioxidant defenses and cause oxidative stress, which damages liver cells over time. This is one of the key reasons chronic heavy drinking leads to liver disease. The backup system also becomes more active with repeated exposure, meaning a regular drinker’s liver literally ramps up its capacity to process alcohol, contributing to tolerance. But that increased capacity comes at the cost of greater cellular damage with every drinking session.
Why Acetaldehyde Is So Harmful
Acetaldehyde does most of the biological damage associated with drinking. It binds directly to DNA, proteins, and cell membranes, forming abnormal chemical bonds called adducts that interfere with normal cell function. These DNA mutations are one mechanism by which alcohol increases cancer risk. Acetaldehyde also triggers oxidative stress in blood vessel walls, promotes inflammation, and damages the energy-producing structures inside cells (mitochondria), causing them to swell and lose their internal structure.
Many of the unpleasant effects people experience after drinking, including facial flushing, headaches, nausea, and eye irritation, are caused by acetaldehyde accumulating faster than the body can clear it. How quickly you clear it depends largely on your genetics.
Genetics and the Flushing Response
Two genetic variations play an outsized role in how your body handles alcohol. The first affects how fast you produce acetaldehyde. People who carry the ADH1B*2 variant (common in East Asian populations) convert ethanol into acetaldehyde up to 100 times faster than those with the standard version of the gene. That means acetaldehyde floods the system quickly after even a small amount of alcohol.
The second, and often more impactful, variation affects how fast you clear acetaldehyde. The ALDH2*2 variant dramatically reduces the activity of the enzyme responsible for breaking acetaldehyde down. People who carry one copy of this variant retain only about 10 to 20 percent of normal enzyme activity. Those who carry two copies have virtually zero activity, meaning acetaldehyde accumulates almost completely in the body after any amount of alcohol.
The worst combination is fast production paired with slow clearance. People with high-activity ADH and low-activity ALDH experience rapid spikes in blood acetaldehyde, triggering an intense flushing reaction: red face, pounding heart, nausea, and headaches from just a few sips. Roughly 8 percent of the world’s population carries the ALDH2*2 variant, with the highest prevalence in East Asian populations. This isn’t just an inconvenience. Chronic drinking with impaired ALDH2 function significantly raises the risk of esophageal and other cancers because of prolonged acetaldehyde exposure.
How Sex Affects Alcohol Processing
Women consistently reach higher blood alcohol levels than men after consuming the same amount of alcohol, and the reason goes beyond body size. Women have significantly less ADH activity in the stomach lining, which means less alcohol gets broken down before it enters the bloodstream. This “first-pass metabolism” in the stomach acts as a filter, and it’s substantially weaker in women.
Women also have a smaller volume of body water relative to their weight (about 7 percent less than men), which means alcohol is distributed into a smaller fluid space, producing higher concentrations. These two factors combined, reduced stomach metabolism and a smaller distribution volume, mean women are more vulnerable to the effects and health consequences of any given amount of alcohol.
How Food Changes the Process
Eating before or while drinking is one of the most practical ways to influence how your body handles alcohol. Food slows gastric emptying, keeping alcohol in the stomach longer where some first-pass metabolism can occur. However, the actual effect on timing may surprise you: in one controlled study, the average time to reach peak breath alcohol was 41 minutes regardless of whether participants had eaten or not.
The more significant effect of food is on peak blood alcohol concentration, which is notably lower when you drink on a full stomach. The elimination rate was actually slightly slower after a meal (0.017 BAC per hour versus 0.020 on an empty stomach), but because the peak was lower to begin with, the total time to reach zero BAC was nearly identical, about five hours in both conditions. In practical terms, food doesn’t speed up alcohol metabolism. It lowers the peak, which reduces impairment and stress on the liver.
How Aging Slows Things Down
As you age, your body becomes less efficient at metabolizing alcohol for several reasons at once. The activity of all three key enzyme systems (ADH, ALDH, and CYP2E1) declines with advancing age. At the same time, total body water decreases, so the same amount of alcohol produces a higher blood concentration. Liver volume and blood flow also decrease in older adults, further reducing the organ’s processing capacity. The combined result is that a drink at 65 hits harder and lingers longer than the same drink at 25, even with identical body weight.
What Your Body Can Process Per Hour
One standard drink in the United States contains about 14 grams of pure alcohol, equivalent to roughly 12 ounces of regular beer, 5 ounces of wine, or 1.5 ounces of distilled spirits. The liver clears approximately 0.015 to 0.020 BAC per hour for most people. In practical terms, that means one standard drink takes roughly one to one and a half hours to fully metabolize, though individual variation based on genetics, sex, age, liver health, and recent food intake can shift this in either direction.
Nothing accelerates this rate. Coffee, cold showers, and exercise do not speed up enzyme activity in the liver. The only variable that meaningfully changes your clearance rate over time is chronic heavy drinking, which upregulates the backup CYP2E1 pathway, but at the cost of increased liver damage and oxidative stress.