Alcohol intoxication, commonly called being “drunk,” is a temporary physiological state resulting from the consumption of ethanol, the psychoactive ingredient found in alcoholic beverages. Ethanol is classified as a central nervous system (CNS) depressant, meaning it slows down brain activity and neural communication. The feeling of being drunk arises when alcohol in the bloodstream interferes with normal brain function, leading to temporary changes in thought, mood, and motor control. This state is defined by the measurable concentration of alcohol circulating throughout the body.
The Journey of Alcohol in the Body
The process of becoming intoxicated begins immediately after the first sip, as alcohol does not require digestion. A small amount is absorbed directly into the bloodstream through the stomach lining. However, the majority of absorption occurs quickly in the small intestine, from where it is rapidly distributed throughout the body by the circulatory system. Because alcohol is water-soluble, it easily travels to all tissues and organs, including the brain.
Once in the brain, ethanol readily crosses the blood-brain barrier to exert its effects on the central nervous system. Alcohol primarily disrupts the balance between the brain’s inhibitory and excitatory neurotransmitters. It enhances the effects of Gamma-Aminobutyric Acid (GABA), the brain’s main inhibitory chemical messenger. This increased GABA activity slows down neural firing, producing the characteristic sedative and relaxing effects.
Simultaneously, alcohol suppresses the activity of Glutamate, the brain’s primary excitatory neurotransmitter. By reducing Glutamate’s ability to excite nerve cells, the brain’s overall activity slows further. This dual action leads to impaired judgment, slurred speech, and delayed reaction times. The brain’s reward centers are also stimulated, leading to initial feelings of euphoria and disinhibition.
Measuring Intoxication: Blood Alcohol Concentration
The scientific metric used to quantify the level of intoxication is the Blood Alcohol Concentration (BAC). BAC measures the amount of alcohol present in the bloodstream and is expressed as a percentage. For instance, a BAC of 0.08% indicates 0.08 grams of alcohol per 100 milliliters of blood. This measurement provides an objective standard for impairment, independent of an individual’s subjective feeling of drunkenness.
A person’s BAC is determined by the rate of alcohol intake versus the rate of metabolism. The body eliminates alcohol primarily through the liver, which contains enzymes that break down ethanol. The liver processes alcohol at a constant and slow pace, typically about one standard drink per hour. When alcohol is consumed faster than the liver can metabolize it, the concentration in the blood rises rapidly, leading to intoxication.
This slow, fixed rate of elimination means the BAC continues to rise even after the person stops drinking, as alcohol is still being absorbed from the stomach and small intestine. BAC is a more reliable measure of impairment than the number of drinks consumed, because it accounts for the concentration of alcohol actively affecting the central nervous system. The rising and falling of this percentage dictates the physical and behavioral symptoms experienced during intoxication.
The Spectrum of Impairment
The effects of alcohol progress through distinct stages as the BAC increases, reflecting a deepening depression of the central nervous system. At the lowest measurable level (0.01% to 0.05% BAC), a person enters the subclinical or euphoria stage. Minor behavioral changes, such as increased talkativeness, mild relaxation, and a feeling of well-being, begin to appear. Though the effects seem mild, judgment and alertness are already slightly lowered.
As the BAC rises to the “excitement” stage (0.09% to 0.25%), the outward signs of impairment become more pronounced. Reaction times slow significantly, and the ability to coordinate movements is visibly reduced, often resulting in unsteadiness or stumbling. Speech may become slurred, and vision can blur, reflecting diminished neurological control over motor and sensory functions. At this point, memory and perception of risk are seriously compromised.
A BAC climbing into the confusion stage (0.18% to 0.30%) indicates a very high level of intoxication. The person becomes confused, drowsy, and may experience severe disorientation. Physical manifestations include significant loss of motor control and a high risk of memory blackouts, where the brain temporarily stops forming new memories. Progression past 0.35% can lead to the stupor and coma stages, where vital functions are dangerously depressed. At these concentrations, breathing, heart rate, and body temperature can drop to life-threatening levels, requiring immediate medical intervention.
Individual Factors Determining How Drunk You Get
The same amount of alcohol can produce widely varying levels of intoxication and BAC in different people due to several biological and environmental factors. Biological sex plays a substantial role because women generally have a lower percentage of body water compared to men. Since alcohol dissolves in body water, a smaller volume of water means the alcohol is more concentrated in the bloodstream, leading to a higher BAC. Furthermore, women typically have lower levels of alcohol dehydrogenase, an enzyme in the stomach that helps break down alcohol before it enters the blood.
Body size and composition are also major determinants of BAC. Individuals with greater body weight have a larger volume of body fluids, which dilutes the alcohol more effectively. Conversely, those with a higher proportion of body fat will have a higher BAC because fatty tissue does not absorb alcohol, leaving the alcohol more concentrated in the remaining body water.
Food consumption significantly affects the rate of absorption and thus the peak BAC level. Drinking on a full stomach slows the process by which alcohol moves from the stomach into the small intestine, delaying its entry into the bloodstream. This slower absorption allows the liver more time to metabolize the alcohol, resulting in a lower maximum BAC. Finally, the speed at which alcohol is consumed is a powerful factor, as rapid drinking quickly overwhelms the liver’s fixed metabolic capacity, causing a steep rise in the concentration of alcohol in the blood.