What happens when you drink alcohol?
After a drink is swallowed, the alcohol is rapidly absorbed into the blood (20% through the stomach and 80% through the small intestine), with effects felt within 5 to 10 minutes after drinking. It usually peaks in the blood after 30-90 minutes and is carried through all the organs of the body.
Most (90%) of the metabolism, or breaking down, of alcohol from a toxic substance to water and carbon dioxide is performed by the liver6, with the rest excreted through the lungs (allowing alcohol breath tests), through the kidneys (into urine) and in sweat.8
The liver can only break down a certain amount of alcohol per hour, which for an average person is around one standard drink8.
The blood alcohol concentration (BAC) rises, and the feeling of drunkenness occurs, when alcohol is drunk faster than the liver can break it down. However, BAC does not correlate exactly with symptoms of drunkenness and different people have different symptoms even after drinking the same amount of alcohol. The BAC level, and every individual’s reaction to alcohol, is influenced by1,2,7:
- the ability of the liver to metabolise alcohol (which varies due to genetic differences in the liver enzymes that break down alcohol)7
- the presence or absence of food in the stomach (food dilutes the alcohol and dramatically slows its absorption into the bloodstream by preventing it from passing quickly into the small intestine)
- the concentration of alcohol in the beverage (highly concentrated beverages such as spirits are more quickly absorbed)
- how quickly alcohol is consumed
- body type (heavier and more muscular people have more fat and muscle to absorb the alcohol)2
- age, sex, ethnicity (eg, women have a higher BAC after drinking the same amount of alcohol than men due to differences in metabolism and absorption – since men have, on average, more fluid in their body to distribute alcohol around than women do, some ethnic groups have different levels of a liver enzyme responsible for the break down of alcohol)
- how frequently a person drinks alcohol (someone who drinks often can tolerate the sedating effects of alcohol more than someone who does not regularly drink).6
The legal drink driving limits for drivers 20 years and over are a breath alcohol limit of 250 micrograms (mcg) of alcohol per litre of breath and a blood alcohol limit of 50mg of alcohol per 100ml of blood. The alcohol limit for drivers under 20 years is zero.