Getting “drunk,” or intoxicated, is the physical and mental state resulting from consuming ethanol, the psychoactive component in alcoholic beverages. Ethanol acts as a depressant on the central nervous system, causing the familiar changes in mood, coordination, and judgment. Intoxication involves the rapid journey of alcohol from the digestive system into the bloodstream and then to the brain, followed by the body’s slow elimination process. Understanding this path, from absorption to metabolism, explains the immediate feelings of a “buzz” and the eventual return to sobriety.
From Drink to Bloodstream
Ethanol does not require digestion, allowing it to be absorbed directly into the bloodstream almost immediately after consumption. While a small amount is absorbed through the stomach lining, the majority is absorbed most rapidly in the small intestine. The speed of absorption depends largely on how quickly the alcohol moves out of the stomach.
The presence of food in the stomach significantly delays gastric emptying, slowing the rate at which alcohol reaches the small intestine and enters the bloodstream. This delay explains why drinking on an empty stomach leads to a much faster rise in blood alcohol levels. As ethanol diffuses into the circulation, its concentration is quantified as Blood Alcohol Concentration (BAC). A higher BAC correlates directly with increased impairment of physical and mental functions.
How Alcohol Affects the Brain
Once in the bloodstream, ethanol easily crosses the blood-brain barrier because it is a small, water-soluble molecule, interfering with brain chemistry. Alcohol is classified as a central nervous system depressant because its primary action is to slow down brain activity by altering key neurotransmitters. It primarily enhances the effects of gamma-aminobutyric acid (GABA), the brain’s main inhibitory neurotransmitter.
By binding to GABA-A receptors, ethanol amplifies the signal that tells neurons to slow down or stop firing, leading to sedative and relaxing effects. This increase in inhibitory signaling contributes to slurred speech, slowed reaction times, and reduced anxiety. Simultaneously, alcohol inhibits the activity of glutamate, the brain’s primary excitatory neurotransmitter. Glutamate promotes nerve transmission and is involved in memory formation and cognitive function.
The suppression of glutamate activity further reduces neural excitability, impairing the ability to think clearly and form new memories. As the BAC rises, alcohol affects different brain regions. It starts with the cerebral cortex, which controls judgment and inhibition. Higher concentrations impact the cerebellum, which governs muscle coordination, resulting in stumbling and loss of balance. The combined effect of enhancing the inhibitory system and suppressing the excitatory system produces the characteristic state of being drunk.
Processing and Elimination
The body begins removing alcohol almost as soon as it is consumed, with the liver performing over 90% of the metabolism. Ethanol is broken down through a two-step enzymatic pathway, starting with the enzyme Alcohol Dehydrogenase (ADH). ADH converts ethanol into acetaldehyde, a highly toxic compound responsible for many unpleasant physical effects.
In the second step, Aldehyde Dehydrogenase (ALDH) quickly converts the toxic acetaldehyde into harmless acetate. Acetate is then broken down into carbon dioxide and water, which the body eliminates. The liver processes alcohol at a relatively fixed, slow rate, regardless of how much was consumed. This fixed rate means the only way to reduce intoxication is to allow time for the liver enzymes to complete their work.
Genetic variations in ADH and ALDH genes can affect the speed of this process. For instance, individuals with less efficient versions of ALDH cause acetaldehyde to build up rapidly. This accumulation results in the “alcohol flush reaction,” characterized by facial redness and nausea. A small amount of alcohol (around 5-10%) is also eliminated unchanged through breath, urine, and sweat.
Factors That Change the Rate of Intoxication
The speed and severity of intoxication are modified by several individual factors, not solely the amount consumed. Body weight is significant because a larger person has a greater volume of body water to dilute the alcohol, leading to a lower BAC for the same amount consumed. Conversely, individuals with a higher percentage of body fat tend to have a higher BAC because alcohol is not readily absorbed into fat tissue.
Biological sex influences intoxication due to differences in body composition and enzyme activity. Women typically have a lower proportion of body water and lower levels of the stomach enzyme ADH, leading to less alcohol breakdown before it reaches the bloodstream. Food consumption significantly slows absorption by delaying the passage of alcohol into the small intestine. Acquired tolerance from regular drinking is partly due to the liver becoming more efficient at producing metabolizing enzymes.