Alcohol, or ethanol, is a common compound found in alcoholic beverages. Its intoxicating effects stem primarily from its interaction with the central nervous system. When consumed, alcohol acts as a depressant, slowing down brain activity and altering cognitive and physical functions. Understanding the biological processes involved reveals how alcohol intoxicates.
Alcohol’s Journey: From Sip to System
Unlike food, alcohol does not require digestion. A small amount can be absorbed directly through the mouth and stomach. However, the majority of alcohol absorption occurs rapidly in the small intestine, which has a much larger surface area for uptake.
Once absorbed, alcohol enters the bloodstream and quickly distributes throughout the body, reaching organs. Blood circulates in about 90 seconds, allowing alcohol to affect the brain and other organs quickly. The full effects of a drink can be felt within 15 to 45 minutes, depending on how fast it is absorbed.
Brain Under Influence: How Alcohol Affects Neurotransmitters
Alcohol acts as a central nervous system depressant, slowing brain activity. This effect is due to its influence on the brain’s neurotransmitters. Alcohol can alter mood, behavior, self-control, and impair memory and clear thinking.
One primary way alcohol acts is by enhancing the inhibitory effects of gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the brain. By increasing GABA activity, alcohol reduces neuronal excitability, leading to feelings of relaxation, drowsiness, and reduced anxiety. Simultaneously, alcohol inhibits the activity of glutamate, the brain’s main excitatory neurotransmitter. This inhibition of glutamate further contributes to slowed brain function, impaired memory formation, and difficulties with clear thought processes.
Alcohol also impacts the brain’s reward system by temporarily increasing dopamine levels. This surge in dopamine contributes to the initial feelings of pleasure often associated with alcohol consumption. The combined effects on these neurotransmitters can result in observable signs of intoxication, such as impaired coordination, slurred speech, altered judgment, and memory blackouts.
Metabolism and Elimination
The body processes over 90% of consumed alcohol in the liver, where it is metabolized for elimination. The process begins with the enzyme alcohol dehydrogenase (ADH), which converts ethanol into acetaldehyde.
Acetaldehyde is a toxic compound, so another enzyme, aldehyde dehydrogenase (ALDH), converts it to acetate. Acetate is then broken down into carbon dioxide and water for elimination. This enzymatic breakdown dictates the rate at which alcohol is removed from the system, around one standard drink per hour. A small percentage of alcohol, about 2-5%, is eliminated unchanged through breath, urine, and sweat.
Individual Differences in Alcohol’s Effects
The impact of alcohol can vary from person to person, influenced by several physiological factors. Body weight and composition play a role, as individuals with higher body water content can dilute alcohol better, leading to lower blood alcohol concentrations. Since alcohol distributes into body water, women reach higher peak blood alcohol concentrations than men for equivalent consumption, partly because women have less body water and more body fat.
Differences in metabolism also contribute to varied effects. Women have lower levels of the enzyme ADH in their stomach, meaning less alcohol is metabolized before it enters the bloodstream. Food intake can slow alcohol absorption because food in the stomach obstructs contact with the stomach lining and delays passage to the small intestine. Genetic variations can influence the activity of metabolizing enzymes like ADH and ALDH, affecting how quickly alcohol is processed. Regular alcohol consumption can also lead to tolerance, requiring more alcohol for the same effect.