How the body metabolizes alcohol into EtG

The short version: two roads, one tiny detour

When you drink, your body treats alcohol as something to get rid of as fast as possible. It does not store it the way it stores fat or sugar. Instead, the liver runs a two-step cleanup that converts almost all of it — more than 95% of the dose — into harmless byproducts that leave as carbon dioxide and water. Alongside that main cleanup, a very small share of the alcohol takes a different chemical route called glucuronidation. That side road produces ethyl glucuronide, or EtG, and it is the entire reason EtG testing exists.

The proportions matter for understanding every EtG result. Because EtG comes from less than 0.1% of the alcohol you drank, an EtG level is not a measure of how drunk you were. It is a sensitive signal that alcohol passed through your system, roughly tracking how much you drank and how recently. A test cutoff — 100, 200, or 500 ng/mL — is simply the line a program draws on that signal.

This article walks the pathway step by step: absorption, the main oxidative road, the glucuronidation side road, and why EtG lingers long after alcohol itself is gone. If you want the practical side — how long EtG stays detectable after your own drinking — our EtG calculator turns this science into an estimated window, and our calculation method page explains the model behind it.

Step 1: From the glass to the bloodstream

Alcohol starts moving into your blood within minutes of the first sip. About 20% is absorbed through the stomach lining, and the rest through the small intestine, which is why drinking on an empty stomach raises blood alcohol faster: food slows the stomach from emptying into the intestine, so absorption stretches out over a longer period. Once in the blood, alcohol spreads through the body's water — which is why a smaller person, or someone with less body water, reaches a higher blood alcohol concentration from the same number of drinks.

A small amount of alcohol is broken down in the stomach itself by gastric alcohol dehydrogenase, but this is a minor contribution. The real work happens in the liver, which processes alcohol continuously at a roughly steady rate — about one standard drink per hour for most adults — no matter how much coffee or water you drink. That fixed pace is why EtG windows are measured in days, not hours: the body cannot be rushed.

Step 2: The main road — ethanol to acetaldehyde to acetate

In the liver, the main cleanup runs in two steps. First, the enzyme alcohol dehydrogenase (ADH) converts ethanol into acetaldehyde. Acetaldehyde is a reactive, toxic compound — it is the main reason heavy drinking feels so unpleasant — so the body does not let it linger. Second, the enzyme aldehyde dehydrogenase (ALDH) converts acetaldehyde into acetate, a harmless compound similar to vinegar, which the body then breaks down further into carbon dioxide and water, or uses for energy.

Both steps consume a helper molecule called NAD+, converting it to NADH — part of why heavy drinking disrupts metabolism more broadly. The pathway also saturates: ADH works at a roughly fixed maximum speed, so when you drink faster than the liver can clear, alcohol simply accumulates in the blood.

Genetics changes the speed of this road. Some people, most famously many people of East Asian ancestry, carry a less active form of ALDH2. Acetaldehyde builds up faster than it can be cleared, causing flushing, nausea, and a rapid heartbeat. The same variation also changes how quickly alcohol is fully cleared, which is one reason EtG windows vary from person to person even at the same dose.

Step 3: The side road — glucuronidation makes EtG

While ADH and ALDH handle the bulk of the alcohol, a small fraction meets a different family of liver enzymes: UDP-glucuronosyltransferases, or UGTs. These enzymes attach a molecule called glucuronic acid — a sugar derivative the body uses to make many substances water-soluble and easier to excrete — directly to the ethanol molecule. The product is ethyl glucuronide. The two UGT forms most active in this reaction are UGT1A1 and UGT2B7, and like ADH and ALDH, they vary between people.

Two properties make EtG special as a biomarker. First, it is a direct metabolite: the body has no other way to make it. EtG in urine can only come from alcohol that passed through the body — or, in rare incidental-exposure cases, from alcohol absorbed through skin or inhaled, which is why our guides on hand sanitizer and mouthwash exist. Second, EtG is highly water-soluble, so the kidneys filter it into urine efficiently. That combination — only made from alcohol, and excreted in urine — is what makes it a useful test target.

A related compound, ethyl sulfate (EtS), forms by a parallel side road using sulfotransferase enzymes, again at roughly 0.05% of the dose. Labs often measure EtG and EtS together because they corroborate each other, but EtG is the standard screening marker and the one most programs set cutoffs for.

Why EtG outlasts alcohol itself

It seems like a paradox: EtG's half-life in blood is only about 2 to 4 hours, yet EtG stays detectable in urine for days. The explanation is that a half-life describes how fast a single batch declines, not how long the body keeps producing and excreting it. EtG keeps forming as long as alcohol remains in the blood, and the kidneys keep filtering it out gradually. Urine also concentrates EtG over time as the bladder collects it between voids, so a urine sample reflects hours of accumulation, not a single moment.

The practical upshot: a breath test or blood alcohol test answers "are you drinking now," while an EtG test answers "have you drunk in the last few days." That is why probation programs, employers, and treatment programs use EtG for monitoring abstinence rather than for catching intoxication — and why our half-life calculator models the decline as a range, not a single clean hour.

What speeds up or slows down EtG formation

The pathway is the same in everyone, but its speed and output vary. The factors below are the ones research consistently shows moving the result — and they are the same factors our calculator asks about, because they move the estimated window.

One factor deserves a clear warning: drinking water does not remove EtG from the body faster. It dilutes the urine sample, which can lower the measured concentration — but laboratories measure creatinine alongside EtG precisely to detect dilute samples, and the EtG-to-creatinine ratio stays roughly unchanged. Our guide on drinking water and EtG levels covers the research in detail.

Real-world scenario: Friday night drinks, Monday morning test

Consider someone who has four standard drinks at a party on Friday night, finishing around midnight, and faces a urine EtG test on Monday morning — about 60 hours later. Here is what the pathway predicts. Alcohol itself is gone by Saturday morning: the liver clears roughly one drink per hour, so four drinks clear in about four to five hours. EtG, though, peaks in the blood in the early hours of Saturday morning and is still being excreted through Saturday and into Sunday. By Monday morning, the question is no longer whether EtG formed — it did — but whether the remaining concentration is still above the program's cutoff.

At a 500 ng/mL cutoff, the most common screening level, many people in this scenario would test below the line by Monday, because the higher cutoff tolerates a larger remaining tail. At a 100 ng/mL cutoff, the stricter level used by many abstinence-monitoring programs, the same person could still test above the line. The body did the same work in both cases; only the line moved. That is why our 100 vs 500 ng/mL cutoff guide matters more than any single number: the cutoff, not the chemistry, often decides the result.

Change one variable and the story changes. Six drinks instead of four pushes the tail later; drinking again on Saturday restarts formation entirely. It is the same pathway, run with different inputs — exactly what a calculator models.

What this means for reading a calculator estimate

Every EtG calculator is, at heart, a simplified model of this pathway: dose in, formation and excretion out, cutoff applied at the end. A good model states its assumptions honestly. Ours uses published detection ranges rather than a single invented constant — for example, it does not pretend that every drink adds exactly the same ng/mL, because the research shows EtG formation is not perfectly linear with dose and varies with the enzyme variants above. That is why our results are ranges: a window of hours, not a promise about a specific hour.

Three practical lessons follow from the biology. First, treat any estimate as a range and plan around its late end, not its early end. Second, remember that the cutoff decides the result as much as the chemistry does — always check which cutoff your program uses before interpreting a window. Third, no calculator can replace a laboratory test when the answer matters: the pathway varies enough between people that only a measured sample settles an individual case. Used that way — as understanding, not as proof — the science behind EtG is genuinely reassuring: it is a direct, well-studied marker, and its limits are known.

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