Alcohol intoxication is a temporary physiological state that occurs when the chemical ethanol is present in the body, leading to changes in mental and physical function. Understanding this process requires tracing the path of ethanol from the moment of ingestion to its action within the central nervous system. The feeling of being “drunk” results from alcohol interfering with the brain’s communication systems. This physiological journey explains the impairment of coordination, judgment, and memory that characterizes intoxication.
Alcohol’s Journey: From Ingestion to BAC
When an alcoholic beverage is consumed, ethanol molecules quickly enter the bloodstream through the digestive tract. Approximately 20% of the alcohol is absorbed directly from the stomach, while the majority passes into the small intestine, which has a larger surface area for rapid absorption. The alcohol swiftly enters the circulatory system and is distributed throughout the body’s tissues.
The level of alcohol in the body is quantified by the Blood Alcohol Concentration (BAC), which measures the amount of alcohol present in the bloodstream. BAC is expressed as a percentage, representing the grams of alcohol per 100 milliliters of blood. The BAC level rises as long as the rate of absorption exceeds the rate at which the body can metabolize it. The peak BAC, which correlates with the highest level of intoxication, is usually reached between 30 and 60 minutes after the last drink.
How Alcohol Hijacks Brain Chemistry
When alcohol reaches the brain, ethanol directly interferes with the body’s primary neurotransmitter systems. Alcohol is a central nervous system depressant, meaning it slows down brain activity. This effect is achieved through its dual action on two major chemical messengers: Gamma-aminobutyric acid (GABA) and Glutamate.
GABA is the main inhibitory neurotransmitter, responsible for calming neural activity. Alcohol enhances GABA’s effect by acting as a positive allosteric modulator at the GABA-A receptors. When alcohol is present, GABA binds more effectively, leading to greater inhibition of neural firing. This heightened inhibitory action causes the sedative effects of alcohol, resulting in symptoms like slurred speech, relaxation, and lack of motor coordination.
Conversely, alcohol suppresses the activity of Glutamate, the brain’s main excitatory neurotransmitter. Alcohol inhibits the function of N-methyl-D-aspartate (NMDA) receptors. By dampening this excitatory system, alcohol impairs the brain’s ability to process new information and form memories. This suppression contributes to reduced judgment, slowed thinking, and memory gaps often experienced during intoxication.
Why Intoxication Levels Vary
Even when two people consume the exact same amount of alcohol, their resulting levels of intoxication can differ significantly due to a combination of physiological variables.
Food Intake
The presence of food in the stomach is a major factor, as a full stomach delays the emptying of alcohol into the small intestine, slowing the rate of absorption and lowering the peak BAC. Without food, the BAC can peak in as little as 30 minutes, but with a large meal, the peak can be delayed for several hours.
Body Composition
Body composition also plays a role because alcohol is highly soluble in water but not in fat. Individuals with greater body mass and a higher percentage of lean muscle tissue contain more water, which dilutes the alcohol across a larger volume, resulting in a lower concentration. Conversely, a person with a smaller body size or a higher percentage of body fat will experience a higher BAC from the same amount of alcohol.
Gender and Genetics
Gender differences in alcohol processing are also noticeable, primarily due to variations in body water content and enzyme activity. Women generally have a lower percentage of total body water than men, meaning the alcohol is less diluted. Additionally, men typically have higher levels of the enzyme alcohol dehydrogenase in the stomach, which allows for a small amount of alcohol metabolism before it ever reaches the bloodstream. Genetic variations in the enzymes that break down alcohol can also influence the rate of metabolism and the intensity of intoxication.
The Body’s Process for Clearing Alcohol
The process of sobering up is entirely dependent on the liver, which metabolizes nearly all the alcohol consumed. This elimination process begins with the enzyme Alcohol Dehydrogenase (ADH). ADH oxidizes the ethanol, converting it into a highly reactive and toxic compound known as acetaldehyde.
Acetaldehyde is responsible for many unpleasant physical effects associated with drinking. A second enzyme, Aldehyde Dehydrogenase (ALDH), quickly converts the acetaldehyde into a harmless substance called acetate. The acetate is then broken down into carbon dioxide and water. The liver metabolizes alcohol at a relatively constant rate, averaging about one standard drink per hour, and this fixed speed determines the duration of intoxication.