Ethanol, the chemical compound in alcoholic beverages, is a central nervous system depressant that produces intoxication. This “drunk” feeling results from ethanol’s ability to alter the chemical messaging system within the brain. Understanding why alcohol makes you drunk involves tracing its path through the body and examining its two-pronged chemical attack on neural communication.
Absorption and Distribution Through the Body
Alcohol does not require digestion, allowing it to enter the bloodstream almost immediately after consumption. A small amount is absorbed directly through the lining of the mouth and stomach, but the majority is rapidly absorbed in the small intestine. From there, it enters the bloodstream, where its concentration is measured as Blood Alcohol Content (BAC).
Once in the bloodstream, alcohol is quickly distributed throughout the body’s tissues because it is both water- and fat-soluble. The circulatory system moves the substance to every organ within minutes. Distribution to the brain, however, is what causes intoxication.
The brain is protected by the blood-brain barrier, which prevents harmful substances from entering the central nervous system. Ethanol’s small molecular size allows it to easily pass through this barrier. Once alcohol penetrates the brain tissue, it disrupts communication between neurons.
Modifying Neurotransmitter Activity
The mechanism of intoxication is alcohol’s interaction with the brain’s chemical messengers, known as neurotransmitters. Alcohol’s primary effect is a dual action that simultaneously increases the brain’s “brakes” while cutting the “accelerator.” This imbalance causes the overall slowing and impairment characteristic of being drunk.
Alcohol acts as a potentiator for Gamma-aminobutyric acid (GABA), the principal inhibitory neurotransmitter. When alcohol binds to the GABA-A receptor, it enhances GABA’s effect, allowing negatively charged chloride ions to flow into the neuron. This influx hyperpolarizes the neuron, making it less likely to fire an electrical signal. This process applies a powerful brake on neural activity, resulting in sedation, relaxation, and reduced anxiety.
Alcohol also inhibits the activity of the major excitatory neurotransmitter, Glutamate. Alcohol acts as an antagonist to the N-methyl-D-aspartate (NMDA) receptor, which Glutamate typically activates to promote neural firing. By blocking Glutamate, alcohol disrupts signaling pathways responsible for cognitive functions like learning and memory formation. This simultaneous increase in inhibition and decrease in excitation explains the depressed state of the central nervous system during intoxication.
The Physiological Manifestations of Intoxication
The chemical imbalance caused by alcohol translates directly into observable physical and cognitive symptoms. These symptoms arise from the suppression of activity in specific brain regions. The frontal cortex, which governs judgment, decision-making, and impulse control, is one of the first areas affected. Suppression of this region leads to impaired judgment and lowered social inhibitions.
Motor coordination and balance are managed by the cerebellum, a structure located at the back of the brain. Alcohol disrupts neural signaling in the cerebellum. This results in the unsteady gait, loss of fine motor control, and slurred speech commonly associated with intoxication.
Memory impairment, often resulting in an alcohol-induced blackout, is due to alcohol’s disruption of the hippocampus. This brain region is responsible for consolidating short-term memories into long-term storage. When alcohol interferes with the Glutamate system, it prevents the necessary cellular changes for memory formation, meaning the events cannot be recorded.
How the Body Processes Alcohol
The state of intoxication ends when the body’s metabolism clears ethanol from the bloodstream. The liver is the primary organ responsible for this detoxification process, handling over 90% of the alcohol consumed. This metabolism involves a two-step enzymatic process.
First, the enzyme Alcohol Dehydrogenase (ADH) converts ethanol into a highly toxic compound called acetaldehyde. Acetaldehyde is responsible for many unpleasant effects of drinking, including flushing and nausea. In the second step, Aldehyde Dehydrogenase (ALDH) rapidly converts acetaldehyde into harmless acetate, which the body breaks down further for elimination.
The rate at which the liver performs this two-step process is relatively constant and cannot be significantly sped up by external factors like cold showers or coffee. The body can metabolize only a fixed amount of alcohol per hour. Intoxication persists until all the alcohol has been processed.