Most people significantly underestimate how long alcohol stays in their system. The feeling of being drunk fades well before the alcohol has actually cleared. That gap between how you feel and what your blood alcohol level actually is causes most of the problems: driving the morning after a heavy night, taking medication too soon, or making decisions that feel fine at the time but are not.
The answer to how long alcohol stays in your system depends on one thing more than anything else: how many units you drank.
- How your body processes alcohol
- The one unit per hour rule
- What actually affects how fast alcohol clears
- The myths that do not work
- What "still over the limit" in the morning means
- Alcohol and medication interactions
- How long alcohol shows up on different tests
- Work out how long your week's drinking takes to clear
How your body processes alcohol
When you drink alcohol, it is absorbed into your bloodstream through the stomach and small intestine. Unlike most nutrients, it does not need to be broken down before absorption. It passes directly into the blood, which is why you feel the effects relatively quickly.
The liver is almost entirely responsible for metabolising alcohol. It converts it into acetaldehyde, then into acetate, then into water and carbon dioxide, which the body expels. A very small amount leaves through breath, sweat, and urine, but this accounts for less than 5% of total alcohol elimination.
The liver cannot be forced to work faster. It processes alcohol at a fixed rate, regardless of what else you do.
The one unit per hour rule
The average adult liver can metabolise approximately one unit of alcohol per hour. One unit is 10ml of pure alcohol. That equates roughly to:
- A single 25ml measure of spirits at 40% ABV
- Half a pint of standard 4% lager
- A small 125ml glass of wine at approximately 8% ABV
The problem is that very few drinks contain exactly one unit. A standard pub pour of wine is 175ml at 13% ABV, which is 2.3 units. A pint of 5% lager is 2.8 units. A large glass of wine at 250ml is around 3.25 units. People routinely think in drinks rather than units, and the two numbers diverge considerably.
If you drank one bottle of wine over an evening, at around 9 to 10 units for a standard 13% bottle, your liver will take 9 to 10 hours to clear it. That is from the point you finished drinking, not the point you started.
What actually affects how fast alcohol clears
The one unit per hour figure is an average. Several factors push that rate up or down for different people.
Body weight and composition
Larger bodies have more water to dilute alcohol in the bloodstream. A heavier person will reach a lower peak blood alcohol concentration from the same number of drinks. However, body composition matters too. Muscle tissue holds more water than fat tissue, so two people of the same weight but different body compositions will process alcohol differently.
Sex
Women generally have lower levels of alcohol dehydrogenase, the enzyme that breaks down alcohol in the stomach before it reaches the bloodstream. This means a higher proportion of the alcohol reaches the blood compared to a man drinking the same amount. Women also tend to have a higher percentage of body fat relative to water, which concentrates alcohol in the blood. The practical result is that the same number of units produces a higher blood alcohol level in most women than in most men of comparable weight.
Age
Liver enzyme activity decreases with age. Older adults generally process alcohol more slowly than younger adults. Body water content also decreases with age, which means less dilution. The NHS guidelines apply to all adults, but the same number of units carries a meaningfully higher risk in someone over 65.
Food
Eating before and during drinking slows the rate at which alcohol is absorbed into the bloodstream. Food, particularly fat and protein, slows gastric emptying. This reduces the peak blood alcohol level and spreads the effect over a longer period. It does not reduce the total amount of alcohol that eventually enters the blood, and it does not speed up how quickly the liver clears it.
Medications
Several common medications interact with alcohol metabolism. Metronidazole and tinidazole cause a severe reaction with alcohol. Paracetamol taken alongside heavy alcohol use increases the risk of liver toxicity. Antihistamines, sleeping tablets, and benzodiazepines amplify the sedative effects of alcohol. Metformin, widely used in type 2 diabetes, carries a risk of lactic acidosis when combined with heavy drinking. If you take regular medication, checking with a pharmacist before drinking is good practice.
The myths that do not work
Several well-established beliefs about sobering up are not supported by evidence. Worth knowing, because acting on them can lead to genuine harm.
Coffee does not sober you up. Caffeine can reduce feelings of drowsiness and make you feel more alert. It does not reduce your blood alcohol level or speed up liver processing in any meaningful way. You can be wide awake and still significantly over the drink-drive limit.
Sleep does not flush out alcohol. While you sleep, your liver continues processing alcohol at the same rate it always does. If you went to sleep with 8 units in your system, you will wake up 7 hours later with roughly 1 unit remaining. You did not sleep it off. Your liver processed it at the same pace it would have anyway.
Water does not speed up elimination. Staying hydrated is sensible. Alcohol is a diuretic and dehydration worsens hangovers. But drinking water does not accelerate how quickly alcohol clears from your blood.
Exercise makes no practical difference. Physical activity marginally increases the rate at which alcohol is expelled through breath and sweat, but this accounts for such a small percentage of total alcohol elimination that it is not a meaningful intervention.
What "still over the limit" in the morning means
The UK drink-drive limit in England, Wales, and Northern Ireland is 80mg of alcohol per 100ml of blood. In Scotland, it is stricter at 50mg per 100ml. Neither of these is zero, but both are lower than most people assume when thinking about the morning after.
If you finished drinking at midnight and had 10 units across the evening, basic arithmetic puts you at roughly 10 hours before your system is clear. That is 10am the following morning, assuming an average processing rate. If you were drinking spirits into the small hours, or had more than 10 units, that window extends further.
The safest approach is to count your units from the point you finished drinking, assume one hour per unit, and add a buffer. You cannot measure your own blood alcohol level without a breathalyser or blood test. The feeling of being fine is not an accurate guide.
Alcohol and medication interactions
The interaction between alcohol and medication is more significant than most people realise. These are the most clinically relevant combinations for people using pharmacy or clinic services.
GLP-1 medications such as semaglutide and tirzepatide slow gastric emptying, which changes how quickly alcohol is absorbed. People on these medications often report feeling the effects of alcohol more quickly and at lower doses than before. Hypoglycaemia risk also increases if alcohol is consumed alongside these drugs.
Antibiotics, specifically metronidazole and tinidazole, cause a disulfiram-like reaction when combined with alcohol. This produces flushing, nausea, vomiting, and rapid heart rate. The advice is no alcohol during the course and for 48 hours after the last dose.
Blood pressure medications, including beta blockers, can have their effects amplified by alcohol. Combined with alcohol's own blood pressure-lowering effect, this can cause dizziness and falls, particularly in older adults.
Anticoagulants such as warfarin are affected by alcohol because alcohol inhibits some of the same liver enzymes involved in warfarin metabolism. Heavy drinking can increase warfarin's effect and raise bleeding risk.
How long alcohol shows up on different tests
Blood alcohol concentration clears roughly in line with the one unit per hour rule. But alcohol leaves other traces that persist longer.
Breath tests measure alcohol in the air you exhale. This correlates closely with blood alcohol concentration and clears on the same rough timeline.
Urine tests can detect alcohol metabolites for longer. Ethyl glucuronide, a metabolite produced when alcohol is broken down, can be detected in urine for up to 80 hours after the last drink, even when blood alcohol has returned to zero. This is relevant for workplace testing and some clinical contexts.
Hair follicle tests can detect alcohol use going back months, based on metabolites incorporated into hair as it grows. These are used in occupational health and legal settings rather than routine clinical practice.
Liver function tests reflect the cumulative effects of alcohol rather than the presence of alcohol at a specific time. GGT, gamma-glutamyl transferase, is the most sensitive marker and can remain elevated for weeks to months after stopping drinking.
Work out how long your week's drinking takes to clear
The one unit per hour rule only works if you know how many units you actually drank. That is harder than it sounds. Drink sizes vary, ABV differs between brands, and home pours rarely match the standard measures used in pubs.
The free Alcohol Units Calculator lets you count up your units across 14 common drinks, including wine, beer, spirits, cider, and prosecco. It shows your weekly total against NHS guidelines and calculates your estimated calorie intake from alcohol.
Once you have that number, you have a realistic basis for working out how long it will take to clear.
This article is for general information only. It is not medical advice. If you are concerned about your drinking, speak to your GP or pharmacist. For a list of support services, visit the NHS website.
