Understanding how long alcohol remains in your body is crucial for safety, health, and legal compliance. While you might feel sober shortly after a drink, alcohol can be detected in your system for much longer than you expect.
On average, it takes the liver about one hour to process a single unit of alcohol. However, traces can linger in your blood for up to 6 hours and in other parts of the body for days or even months.
In the UK, one unit of alcohol is roughly equivalent to what the body can process in an hour. Standard servings include:
1/2 pint of lower-strength beer, lager, or cider.
A small glass of wine.
A single shot (25ml) of spirits (gin, vodka, whisky, or rum).
Note: Many modern drinks are stronger or served in larger portions, meaning a single glass often contains 2 or 3 units.
The “detection window” varies significantly depending on the biological sample being tested.
| Test Method | Detection Window |
| Blood | Up to 6 Hours |
| Breath (Breathalyser) | 12 to 24 Hours |
| Saliva | 12 to 24 Hours |
| Urine | 12 to 72+ Hours (depending on test sensitivity) |
| Hair | Up to 90 Days |
Alcohol is absorbed rapidly into the bloodstream, with most people feeling the effects within 15 to 45 minutes. Once absorbed, it is primarily broken down in the liver by an enzyme called alcohol dehydrogenase.
Several factors influence how quickly your body clears alcohol, including:
Age and Weight: Larger individuals may dilute alcohol more effectively, while metabolism often slows with age.
Gender: Biological factors typically mean women process alcohol differently than men.
Food Intake: Eating before drinking slows the absorption of alcohol into the blood.
Liver Health: A damaged liver takes significantly longer to filter toxins.
In England, Wales, and Northern Ireland, the legal drink-drive limit is 80 milligrams of alcohol per 100 millilitres of blood. However, there is no “safe” amount to drink before driving.
Even small amounts of alcohol—well below the legal limit—can impair your:
Reaction times
Peripheral vision
Coordination and judgment
The safest approach is simple: If you are driving, do not drink at all.
As your Blood Alcohol Concentration (BAC) rises, the effects on your Central Nervous System become more pronounced. Common signs of being “drunk” include:
Impaired Coordination: Alcohol affects the inner ear and cerebellum, leading to unsteadiness.
Cognitive Issues: Slurred speech, confusion, and difficulty concentrating.
Lowered Inhibitions: Leading to risky behaviors or poor decision-making.
Respiratory Depression: In severe cases, alcohol can slow breathing to dangerous levels.
Risks of Heavy Drinking
Excessive consumption significantly increases the risk of road traffic accidents, violent incidents, and self-harm. Furthermore, alcohol-related admissions at Accident & Emergency (A&E) departments are common.
Because A&E operates on a priority basis, those admitted for simple intoxication without life-threatening injuries often face wait times of many hours.
While the liver breaks down most of a single small drink in about an hour, alcohol remains detectable in the blood for up to 6 hours and in the urine for up to 3 days. Always prioritize safety by understanding your limits and never drinking before operating a vehicle.
For more detailed information on units and health, visit the NHS alcohol advice page.
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