Alcohol intoxication is a physiological process that begins the moment alcohol enters the body. It involves absorption into the bloodstream, distribution throughout the body, and ultimately affects brain chemistry and function. This journey clarifies why alcohol consumption leads to the familiar signs of intoxication.
From Drink to Bloodstream
Alcohol begins entering the bloodstream almost immediately upon consumption. A small amount is absorbed through the lining of the mouth, but the primary sites of absorption are the stomach and, more significantly, the small intestine. Approximately 20% of ingested alcohol is absorbed directly from the stomach, while the remaining 80% rapidly enters the bloodstream through the small intestine’s large surface area. Unlike food, alcohol does not require digestion before it can be absorbed.
Once absorbed, alcohol circulates quickly throughout the body via the bloodstream, reaching various organs within minutes. The rate at which blood alcohol concentration (BAC) peaks can vary, typically occurring between 30 and 90 minutes after consumption, depending on several factors.
Alcohol’s Effects on the Brain
Alcohol is classified as a central nervous system (CNS) depressant, slowing brain activity and neural communication. It achieves this by altering the balance of key neurotransmitters, the brain’s chemical messengers. Specifically, alcohol enhances the effects of gamma-aminobutyric acid (GABA), the brain’s primary inhibitory neurotransmitter. Alcohol binds to GABA-A receptors, increasing the influx of chloride ions into neurons, which makes them less excitable and slows down their signaling.
Simultaneously, alcohol inhibits the activity of glutamate, the main excitatory neurotransmitter in the brain, particularly at N-methyl-D-aspartate (NMDA) receptors. This dual action reduces overall brain activity. The resulting neurological changes include impaired judgment, reduced inhibitions, slurred speech, poor coordination, and slower reaction times. Alcohol also influences the release of dopamine in the brain’s reward pathways, contributing to the initial pleasurable sensations many people experience.
The Body’s Alcohol Processing
The body primarily processes and eliminates alcohol through the liver, which metabolizes 90% or more of the ingested alcohol. This involves enzymatic reactions. The enzyme alcohol dehydrogenase (ADH) first converts ethanol, the alcohol in beverages, into acetaldehyde. Acetaldehyde is a toxic compound.
Following this, another enzyme, aldehyde dehydrogenase (ALDH), rapidly converts the toxic acetaldehyde into acetate, a much less harmful substance. Acetate is then further broken down into carbon dioxide and water for elimination. A small percentage of alcohol, typically between 5% and 10%, is eliminated unchanged through breath, urine, and sweat. The liver processes alcohol at a relatively constant rate, averaging about one standard drink per hour.
Why Intoxication Varies
The degree of intoxication varies significantly among individuals due to several factors. Body weight plays a role, as individuals with less body mass or a higher proportion of body fat tend to have a higher concentration of alcohol because there is less water to dilute it. Gender also contributes to these differences; women typically have a lower percentage of body water and less gastric alcohol dehydrogenase (ADH) enzyme activity than men. These physiological differences lead to higher blood alcohol concentrations and faster intoxication in women compared to men who consume the same amount of alcohol.
Food consumption before or during drinking can slow down alcohol absorption by delaying its passage from the stomach to the small intestine. Genetic variations in the ADH and ALDH enzymes can also affect how quickly an individual metabolizes alcohol. Some genetic variants lead to less active ALDH, causing acetaldehyde to build up and resulting in unpleasant physical reactions like flushing, which can deter heavy drinking. The speed of consumption and developed tolerance also influence intoxication.