Alcohol science
From the first sip to the last molecule: a complete guide to how alcohol is absorbed, distributed, metabolised, and eliminated, and why the rate varies so much between individuals.
Standard elimination rate
~0.015% BAC/hour
Average adult; broad range about 0.010-0.035%
Liver processing capacity
~1 standard drink/hour
At typical alcohol doses
First-pass metabolism
Up to 20%
Alcohol broken down before reaching bloodstream
Reference only
This calculator uses a Widmark-style formula for estimation only. Individual results vary based on metabolism, food intake, medications, health, and drink accuracy. Never use this tool to decide whether you are safe to drive, work, or perform safety-critical tasks.
Body timeline
From the moment you take a drink, alcohol moves through absorption, distribution, metabolism, and elimination.
Section 1
Alcohol absorption occurs primarily in two locations: the stomach and the small intestine. The stomach absorbs alcohol relatively slowly, while the small intestine absorbs it quickly because it has a much larger surface area. Gastric emptying, or how fast alcohol leaves the stomach, is therefore a major determinant of how quickly BAC rises.
Food slows gastric emptying and keeps alcohol in the stomach longer. A meal high in fat and protein has the strongest buffering effect, lowering peak BAC and delaying the time to peak even when the total alcohol dose is the same.
Carbonated drinks such as sparkling wine, beer, and spirits mixed with carbonated mixers can speed gastric emptying. That is one reason sparkling drinks may feel faster than still drinks with similar alcohol content. The beer vs wine vs spirits guide compares absorption speed across drink types.
First-pass metabolism means some alcohol is broken down before it reaches the main bloodstream. ADH in the stomach lining and liver performs part of this early breakdown. Lower gastric ADH activity, chronic heavy drinking, and some H2 blockers can reduce first-pass metabolism, allowing more alcohol into the blood. See alcohol and medications for the medication side.
Section 2
Alcohol metabolism is not one reaction. It is a sequence of pathways that convert ethanol to acetaldehyde, acetaldehyde to acetate, and acetate to carbon dioxide and water.
| Pathway | Primary Enzyme | When Active | Rate | Key Products | Notes |
|---|---|---|---|---|---|
| ADH pathway | ADH -> ALDH | All drinking levels | Fixed, about 1 drink/hr | Acetaldehyde -> acetate -> CO2 + H2O | Primary pathway; rate-limiting at typical doses. |
| MEOS / CYP2E1 | CYP2E1 | High BAC; chronic drinkers | Inducible | Acetaldehyde + reactive oxygen species | Induced by chronic drinking; metabolises many medications. |
| Catalase pathway | Catalase | Minor contribution | Very slow | Acetaldehyde | Minor overall; may be relevant in some tissues. |
The ADH pathway is dominant at typical drinking levels. At higher alcohol concentrations and in chronic heavy drinkers, CYP2E1 becomes more important. Catalase contributes only a small fraction of whole-body alcohol metabolism.
Acetaldehyde is the key intermediate. It is much more toxic than ethanol and must be converted to acetate by ALDH. Reduced ALDH2 activity causes acetaldehyde accumulation, flushing, nausea, rapid heartbeat, and a higher long-term risk profile with regular drinking.
Section 3
The standard alcohol elimination rate used in many BAC tools, about 0.015% BAC per hour, is a population average. It reflects how fast the liver processes alcohol after absorption and distribution. The how BAC works guide explains how this rate is applied in Widmark-style estimates.
Real elimination rates vary widely. Many people fall around 0.012-0.020% per hour, but the broader range can be about 0.010-0.035% per hour depending on liver health, genetics, chronic drinking, age, sex, medication use, and other factors. Detection windows in the how long does alcohol stay guide are built around this uncertainty.
Despite the variability, an average rate is still useful for planning. The practical rule is to treat any result as a minimum estimate and add a safety margin, especially if liver health, medications, or unusually heavy drinking are involved. Medication effects are covered in the alcohol and medications guide.
| Factor | Effect | Mechanism |
|---|---|---|
| Chronic heavy drinking | Faster | CYP2E1 induction increases metabolic capacity |
| Liver disease | Slower | Reduced hepatic ADH and ALDH activity |
| Sex: female | Slightly slower | Lower gastric ADH activity and lower body water on average |
| Age: older | Slower | Reduced liver mass and enzyme activity |
| Fasting / malnutrition | Slower | Reduced cofactor availability for ADH |
| Genetic ADH variants | Variable | ADH variants affect ethanol-to-acetaldehyde conversion |
| Genetic ALDH2 variant | Different risk profile | Acetaldehyde accumulates, causing flushing and higher cancer risk |
| Medications | Variable | Some compete for or induce metabolic enzymes |
| High BAC | Variable | ADH saturation and MEOS contribution change with dose |
| Fever | Slightly faster | Higher temperature can increase enzyme activity |
Section 4
Alcohol distributes into body water, not body fat. A heavier person with more total body water dilutes the same alcohol dose into a larger volume, producing a lower BAC. Two people of the same weight can still differ if one has more muscle and therefore more body water.
Women typically reach higher BAC levels than men after the same dose per kilogram because body water percentage and first-pass metabolism differ on average. The Widmark formula reflects this with different distribution constants.
ADH variants affect how quickly ethanol becomes acetaldehyde. ALDH2 variants affect how quickly acetaldehyde clears. Fast ADH plus slow ALDH can produce flushing, nausea, rapid heartbeat, and a different long-term risk profile.
Food slows gastric emptying and lowers peak BAC. Hydration does not speed alcohol metabolism, but dehydration concentrates alcohol in less body water and worsens symptoms such as headache and fatigue.
Tolerance can make someone feel less impaired at the same BAC through brain adaptation and learned compensation. It does not make driving performance safe. For more, see alcohol and driving.
Some medicines compete for liver enzymes, inhibit first-pass metabolism, or amplify impairment without changing BAC. Liver disease, diabetes, and other conditions can also shift the real clearance rate.
Personal estimate
The following factors can shift your personal elimination rate above or below the standard 0.015% per hour average. Select the factors that apply to you to see an adjusted estimate.
Select factors that apply to you
Result
Estimated range: 0.010 - 0.020 %BAC/hour
Average reference: 0.015 %BAC/hour. Most people fall somewhere near this range, but the real value can differ with liver health, genetics, drinking history, age, sex, body composition, and medication use.
Section 5
Many long-term alcohol harms are driven not only by ethanol itself, but by acetaldehyde, the first product of alcohol oxidation. Acetaldehyde can damage DNA, bind to proteins and DNA, and trigger inflammatory responses. It is one reason alcohol is linked with several cancers and with liver injury.
Chronic alcohol-related liver damage often progresses from fatty liver to alcoholic hepatitis and, in some heavy drinkers, cirrhosis. Fatty liver can be reversible with abstinence, but cirrhosis is scarring that seriously reduces liver function, including alcohol metabolism.
Alcohol and acetaldehyde also affect the brain, pancreas, heart, and gastrointestinal tract. Chronic heavy use can contribute to cardiomyopathy, pancreatitis, neurodegeneration, and increased cancer risk in the mouth, throat, oesophagus, liver, colon, rectum, and breast.
Section 6
The liver metabolises alcohol at a rate determined by enzyme capacity. Common interventions do not meaningfully accelerate that process. Time is the only reliable method, and the sober-up calculator applies that timing assumption to a BAC estimate.
| Intervention | Effect on BAC | Effect on Impairment | Verdict |
|---|---|---|---|
| Coffee / caffeine | None | Makes you feel more alert; does not restore reaction time | ❌ Myth |
| Cold shower | None | No meaningful effect on impairment | ❌ Myth |
| Exercise | Negligible | No meaningful effect | ❌ Myth |
| Eating after drinking | None | Food before drinking helps; food after absorption does not lower BAC | ❌ Myth |
| Drinking water | None | Reduces dehydration symptoms only | ❌ Myth |
| Vomiting | Minimal | Only matters if alcohol has not yet been absorbed | ❌ Myth |
| Sleep | None | Rest helps after BAC falls but does not speed metabolism | ✅ Useful |
| Time | Reduces BAC | Impairment falls as BAC falls | ✅ Useful |
| Activated charcoal | None | Does not bind alcohol meaningfully after absorption | ❌ Myth |
| B vitamins / supplements | None | May treat deficiency in some people, but does not lower BAC | ❌ Myth |
Related pages
The Widmark formula and how BAC is calculated: the practical application of the metabolism science on this page.
Detection windows for blood, breath, urine, and hair, based on the elimination rates explained here.
How medications interact with the ADH and CYP2E1 pathways described on this page, and why some combinations are dangerous.
Calculate your BAC using the Widmark formula, with the elimination-rate science from this page applied to your drinks.
FAQ
Common questions about alcohol processing, elimination speed, acetaldehyde, sex differences, and sober-up myths.
Alcohol is primarily metabolised in the liver by alcohol dehydrogenase, which converts ethanol to acetaldehyde. Aldehyde dehydrogenase then converts acetaldehyde to acetate, which is further broken down to carbon dioxide and water. At high alcohol concentrations or with chronic heavy drinking, the MEOS/CYP2E1 pathway also contributes.
The average adult elimination rate is about 0.015% BAC per hour, roughly one standard drink per hour at typical doses. Real rates vary, often from about 0.010% to 0.035% per hour, depending on genetics, liver health, drinking history, age, sex, medications, and other factors.
BAC and impairment vary because of body water, weight, sex, food intake, drinking speed, genetics, tolerance, liver function, medications, and health conditions. The same drink count is not the same dose for every body.
Acetaldehyde is the first metabolic product of alcohol oxidation. It is more toxic than ethanol and contributes to inflammation, cellular damage, and cancer risk. People with reduced ALDH2 activity can accumulate acetaldehyde quickly, causing flushing and a higher risk profile with drinking.
No. Coffee can make someone feel more alert, but it does not lower BAC or restore reaction time, divided attention, or judgement. Time is the only reliable way for BAC to fall.
Women typically have a lower body-water percentage and lower gastric alcohol dehydrogenase activity on average, so the same alcohol dose can produce a higher BAC. The Widmark formula accounts for this with different distribution constants.