How long does alcohol stay in your system?

When alcohol enters your system, your body will begin to metabolise it. Metabolism is the body’s chemical process for breaking down a substance to be absorbed or used as energy. This process happens when you consume any food or drink.

When you consume alcohol, the metabolising process is done primarily by your liver. On average, a person will metabolise the equivalent of one alcoholic drink per hour, but this can vary based on your weight, height, gender and body composition.

Read on to find out more about how long alcohol stays in your system, including parts of the body like blood, urine, saliva and hair.

How long does alcohol stay in the body?

The amount of time that alcohol can be detected in your system can vary depending on how much you’ve consumed, the type of test used and individual biological factors.

Alcohol detection tests can detect alcohol in your body for up to 6 hours after your last drink, while breath, saliva and urine tests can detect alcohol 12 to 24 hours after use. It can be detected up to 90 days after consumption in hair follicles.

• Blood test – a blood test will show alcohol present in your bloodstream for up to 6 hours after your last alcoholic drink
• Urine test – alcohol can be detected in your urine for approximately 12 to 14 hours after alcohol was last consumed
• Breath test - a breathalyser can detect alcohol on the breath for approximately 12 to 14 hours after your last drink
• Saliva test - alcohol can be detected in saliva for approximately 12 to 14 hours after alcohol was last consumed
• Hair test – traces of alcohol can remain in your hair and hair follicles for up to 90 after last consuming alcohol

How is alcohol measured in your body?

When you take a test that measures how much alcohol is in your system, it’s not the total amount of alcohol drunk that’s measured. Alcohol tests measure your blood/breath alcohol concentration (BAC) levels. Your BAC shows the amount of alcohol in your bloodstream or breath, shown by how much ethanol (in grams) is in 100 millilitres of blood or 210 litres of breath.

BAC can be used in breath, blood or urine tests, and is usually displayed as a decimal. One standard drink typically increases BAC levels by 0.02 in the 45 to 60 minutes it takes for your body to absorb the alcohol (source). One standard drink is the equivalent to:

• A can of 5% strength beer (12 fluid ounces)
• A small glass of 12% strength wine (5 fluid ounces)
• A single shot of 40% spirits, such as gin, whiskey or rum (1.5 fluid ounces)

On average, your body is able to absorb one standard drink every 60 minutes – reducing your BAC levels by around 0.16. So, if you consume an alcoholic drink every hour, your BAC levels will continue to increase.

What impacts how long alcohol stays in your system?

Many factors impact how long alcohol remains in your system, not least the amount of alcohol you have consumed. Some of the other things that might affect how long it takes your body to metabolise alcohol include:

• Gender: Generally, women have a higher percentage of fat and a lower percentage of water in their bodies than men. This isn’t true of everyone, but it can lead to alcohol staying in a woman’s system for longer
• Food: Alcohol is absorbed in your digestive tract, so the presence of food makes this process slower – leading to alcohol staying in your system for longer. However, it does help to reduce the feelings you get from drinking alcohol, this is, how ‘drunk’ you feel
• Body composition: People with smaller body frames are likely to have higher levels of BAC from the same amount of alcohol as someone who is taller than them, due to the higher concentration of alcohol in smaller bodies
• Medication: Some medications, such as antidepressants and antibiotics, can affect how your body processes alcohol. Always consult your doctor for advice if you plan to consume alcohol while using medication

How long does it take to feel the effects of alcohol?

Once you’ve had an alcoholic drink, you’ll likely start to feel the effects within just a few minutes. Alcohol starts to absorb in your stomach and small intestine very quickly after consumption. From there, it travels into your bloodstream, which then transports it across your entire body. When transported to the brain, alcohol can impair messages being made there, affecting your emotions, movement and senses.

The factors that impact how long alcohol stays in your system are at play again here. Body composition, your gender, if you’ve recently eaten and any medication you’re taking can all influence how quickly, and how severely, you feel the effects of alcohol once you’ve consumed it.

How long after drinking can you drive?

The rate of alcohol metabolism varies from person to person. While the body typically metabolises one unit of alcohol per hour on average, this doesn’t necessarily mean you’ll be fit to drive the next morning after drinking.

When considering driving after consuming alcohol, you should take into account several factors:

• The time of your last drink
• The type of beverages you consumed
• The total amount of alcohol you’ve consumed

If you need to drive, it’s safest to avoid drinking any alcohol beforehand.

Drink drive limit in the UK

In England, Wales, and Northern Ireland, you're allowed up to 80 milligrams of alcohol for every 100 millilitres of blood, or 35 micrograms of alcohol for every 100 millilitres of breath you exhale.

In Scotland, the rules are stricter. You're only allowed up to 50 milligrams of alcohol for every 100 millilitres of blood, or 22 micrograms of alcohol for every 100 millilitres of breath.

In the context of drink driving limits, this measurement doesn't refer to the total amount of alcohol consumed, but rather the amount of alcohol per 100 millilitres of blood in your body. This concentration can be influenced by several factors including the amount of alcohol you've consumed, how quickly you've drunk it, your metabolism, your weight, and your sex, among other factors.