How Does the Body Process Alcohol? From First Sip to Acetaldehyde to Acetate

Your body processes alcohol mainly in the liver, where alcohol dehydrogenase (ADH) turns it into toxic acetaldehyde and aldehyde dehydrogenase (ALDH2) turns that into acetate, at a fairly fixed pace of about 7 grams an hour that coffee, water or exercise can't meaningfully speed up.¹ A US standard drink contains 14 grams of alcohol, so for many adults one drink takes one to two hours to clear, not the single hour people often quote.^{2, 3}

What happens when you take a drink? Absorption in the stomach and intestine

Alcohol passes into your blood through the stomach wall and, more quickly, through the first stretches of the small intestine.¹ So anything that keeps alcohol in your stomach longer, food above all, slows how fast your blood alcohol rises.

Ethanol mixes freely with water. Once absorbed, it spreads through your body in proportion to each tissue's water content.¹ That's why the same drink produces a higher blood alcohol concentration (BAC) in a smaller person, or in anyone with less body water.

Food is the biggest brake. Cederbaum's review calls whether you drink "on an empty stomach or together with or after a meal" the major factor in absorption speed, and meals high in fat, carbohydrate or protein slow stomach emptying equally well.¹ Food also nudges clearance up a little: blood alcohol typically falls 10–15 mg/100 mL an hour when fasting and 15–20 after a meal.³

First-pass metabolism. The stomach lining has some ADH of its own and breaks down a little alcohol before it reaches the blood. In a 1990 study of 20 men and 23 women, first-pass metabolism in women without alcohol problems was 23% of men's.⁸ How much this matters in everyday drinking is still argued over; Cederbaum calls it "controversial."¹

Blood from your gut flows to the liver first, and the liver does most of the work from there. Less than 10% of alcohol leaves unchanged in breath, sweat and urine.¹ The small fraction in your breath is what a breathalyzer reads, and it's why you can't sweat a drink out.

Step one: how does the liver turn alcohol into acetaldehyde? (ADH and CYP2E1)

Inside liver cells, alcohol dehydrogenase (ADH) converts ethanol into acetaldehyde. A backup system built around an enzyme called CYP2E1 does the same job and takes a bigger share in people who drink heavily over time.¹

ADH sets the pace. The reaction uses up a helper molecule, NAD+, and alcohol breakdown "is generally limited by the maximum capacity of ADH."¹ Once ADH is working flat out, extra drinks simply wait their turn. That's why clearance stays roughly constant instead of speeding up when there's more alcohol to handle.

CYP2E1 is the backup. It needs about a tenfold higher alcohol concentration than ADH to work well, handles roughly 10% of the liver's capacity at low concentrations, and increases with chronic drinking.¹ That's one reason people who drink heavily, but don't yet have liver disease, often clear alcohol faster.³ CYP2E1 also helps convert a small share of acetaminophen (Tylenol) into a toxic byproduct, which is part of why heavy drinking and acetaminophen are a risky pair.⁹

Step two: what happens to acetaldehyde? (ALDH2)

Acetaldehyde is the dangerous middle step. An enzyme in the mitochondria, aldehyde dehydrogenase 2 (ALDH2), converts most of it to acetate, so circulating acetaldehyde levels are normally low.¹

Acetaldehyde is reactive. It latches onto proteins, forming "adducts" that can stop them working.¹ It also binds to and damages DNA, one way alcohol causes cancer according to the US Surgeon General's 2025 advisory.¹² The International Agency for Research on Cancer (IARC) classifies acetaldehyde associated with drinking as carcinogenic to humans (Group 1).¹³

Acetate is the end of the alcohol-specific road: much of it leaves the liver for other tissues, which turn it into carbon dioxide, fatty acids and other everyday molecules.¹

You can see what happens when step two stalls. The medication disulfiram blocks ALDH, so drinking while taking it causes unpleasant symptoms.^{1, 14} Some people are born with a version of ALDH2 that barely works, with a similar effect. For more, see what acetaldehyde is and why it matters.

How fast does the liver metabolize alcohol?

On average, about 7 grams of alcohol an hour for a 70-kg (154-lb) adult, or roughly 170–240 grams a day at full capacity.¹ A US standard drink contains 14 grams of pure alcohol, so at that average, one drink takes about two hours.²

In blood-alcohol terms, a 2010 review puts 15 mg/100 mL an hour (a drop of 0.015 percentage points of BAC) as a good average for moderate drinkers, within a range of about 10–35. Heavy drinkers admitted for withdrawal treatment can reach 25–35 because their CYP2E1 is ramped up.³

So a safer rule of thumb than "one drink an hour" is this: for many adults, each standard drink takes one to two hours to clear, and nothing has been shown to meaningfully speed that up.^{1, 3, 10} Two more catches:

• Your drink may not be one drink. A standard drink is 12 oz of 5% beer, 5 oz of 12% wine or 1.5 oz of 40% spirits. A 12-oz beer at 10% is two, and NIAAA notes that standard sizes "may not reflect customary serving sizes."² See what counts as a standard drink.
• BAC can keep rising after you stop. Alcohol still in your gut keeps being absorbed, so blood alcohol can climb after the last drink, even in someone who is unconscious.¹⁵

That's how alcohol can still be in your blood the next morning. Our guide to how long alcohol stays in your system runs the numbers for blood, breath, urine and hair tests.

Why does alcohol hit people differently? Sex, body size, food, genetics and medications

People absorb, distribute and clear alcohol differently, so elimination rates vary three- to fourfold.¹ The main reasons:

• Body size and body water. A smaller body ends up with a higher alcohol concentration from the same drink.¹
• Sex. Pound for pound, women have less body water than men, so a woman's BAC will tend to be higher than a man's of the same weight after the same amount.¹⁶ Women also showed less first-pass metabolism in the 1990 study above.⁸ And women who regularly drink too much are more likely than men drinking the same amount to develop alcohol-associated hepatitis.¹⁶
• Food. Eating before or while you drink slows absorption, whatever the meal.¹
• Genetics. The ALDH2*2 variant makes an inactive enzyme: two copies leave no detectable ALDH2 activity, and one copy cuts it more than 100-fold. At least 540 million people worldwide are ALDH2-deficient.⁴ Versions of the ADH genes also differ by ancestry and can modestly change clearance speed.¹ See Asian flush and ALDH2.
• Drinking history. People who drink heavily, without liver disease, often clear alcohol faster because CYP2E1 increases.^{1, 3} That's the liver adapting to a heavy load, not a sign it's coping well.
• Medications. Alcohol can make some medicines less effective or even toxic, can add to side effects such as drowsiness and dizziness, and can interact with medicines even when the two aren't taken at the same time.¹⁷

The current Dietary Guidelines say some people should avoid alcohol completely: pregnant women, people recovering from alcohol use disorder or unable to control how much they drink, and people taking medications or with conditions that interact with alcohol.¹⁸

Can you speed up alcohol metabolism?

Not in any way that matters. Your liver's main enzyme is already working near its maximum, and the popular shortcuts don't change that.¹

• Coffee, cold showers and walking don't reverse the effects of alcohol, and NIAAA warns they can make things worse in an overdose.¹⁵
• Water helps with thirst, but in a 2026 randomized crossover trial in 13 Japanese men (some authors worked for a drinks company), water alongside sake didn't change breath alcohol or acetaldehyde.¹⁹
• Sweating it out can't work, because less than 10% of alcohol leaves through breath, sweat and urine combined. Most exercise studies show at most a small increase in elimination.¹

Only time brings your blood alcohol down. NIAAA says the same about hangovers: there's no cure other than time.¹⁰

Where do hangovers, flushing and liver damage come in?

Hangovers. Symptoms peak as blood alcohol returns to about zero and can last 24 hours or longer.¹⁰ Higher blood alcohol and slower elimination are linked to worse hangovers, but in a review of biomarker studies, blood acetaldehyde wasn't significantly associated with hangover severity.²⁰ See what causes a hangover.

Flushing. In people with low ALDH2 activity, acetaldehyde builds up and causes facial flushing, nausea and a fast heartbeat. The flush is a warning sign: in case-control studies from Japan and Taiwan, drinkers with one copy of the variant had 3.7 to 18.1 times the odds of esophageal cancer, after accounting for how much they drank.⁴ No supplement makes drinking safer for people who flush.

The liver. Breaking down alcohol shifts the liver's chemistry, and acetaldehyde damages proteins.¹ Over time, heavy drinking causes fatty liver, which develops in more than 90% of problem drinkers who have 4–5 standard drinks a day for decades; about 35% of problem drinkers develop advanced liver disease. Stopping drinking resolves fatty liver and improves survival even in cirrhosis.²¹ Our guide to liver support after drinking covers what actually helps.

Cancer. The Surgeon General's advisory links alcohol to at least seven cancers, including breast, colorectal, esophageal, liver, mouth, throat and voice-box cancers.¹²

Can supplements change alcohol metabolism? What research shows

No supplement has been shown to speed up alcohol or acetaldehyde clearance in people in a way you could rely on. The most-discussed candidate, dihydromyricetin (DHM), a plant flavonoid found in vine tea (Ampelopsis grossedentata), has conflicting animal results and no human data on this question.⁷

• Injected, in mice: in a 2020 study, DHM injected into the abdomen of alcohol-fed mice increased the enzymes ADH1 and ALDH2 and lowered blood ethanol and acetaldehyde after an alcohol dose.⁵
• By mouth, in rats: a 2020 Czech study gave rats DHM by stomach tube along with alcohol and found no change in how fast alcohol was cleared or in ADH activity. Groups were tiny (as few as two animals in one test), and ALDH wasn't measured.⁶

The route matters. Injection bypasses the gut, and DHM swallowed by rats is poorly absorbed, with only about 4% reaching the bloodstream.²³ Absorption in people hasn't been measured. A 2026 systematic review of 22 studies found DHM's effects on alcohol metabolism inconsistent and no clinical trials of DHM on its own.⁷ Trials of Hovenia dulcis extracts, which contain less than 1% DHM, don't settle it:⁷ in a crossover trial in 26 Korean men who each carried one copy of the ALDH2 variant, a Hovenia fruit extract didn't change blood alcohol or acetaldehyde.²⁴ For the mechanism story, see how DHM works.

The practical takeaway: whatever a label says, assume your body clears alcohol at its usual pace. No supplement makes it safe to drive or makes heavier drinking safer.

What we don't know yet

• Your personal rate. With a three- to fourfold spread between people, no chart or app can tell you exactly how fast you clear alcohol.¹
• How much first-pass metabolism matters in everyday drinking is still debated.¹
• Whether any supplement changes alcohol handling in people. For DHM, animal results conflict and human data don't exist yet (as of October 2026).⁷

What we do know is enough to act on. The 2025–2030 Dietary Guidelines put it simply: "Consume less alcohol for better overall health."¹⁸ And because hangovers impair attention and coordination even after BAC is back to zero, don't drive the morning after a heavy night either.¹⁰

Published by Fuller Health, which makes After Party. This article is general information, not medical advice: talk to a doctor or pharmacist about your own health, medicines and drinking. Last reviewed October 9, 2026. How we research and write.