Alcohol works by slowing down your brain. Ethanol, the type of alcohol in drinks, enhances your brain’s main inhibitory chemical signals while suppressing the excitatory ones, tipping the balance toward sedation, relaxed inhibitions, and impaired coordination. But the full picture involves more than just your brain. From the moment you take a sip, your body launches a complex process of absorption, neurochemical disruption, and metabolism that explains everything from the initial buzz to the next-morning hangover.
How Alcohol Gets Into Your Blood
Alcohol is absorbed slowly from the stomach and rapidly from the small intestine. This means the speed at which your stomach empties its contents is the single biggest factor controlling how fast alcohol hits your bloodstream. When your stomach empties quickly, alcohol reaches the small intestine sooner and absorption is fast. When emptying slows down, peak blood alcohol levels drop and the effects take longer to kick in.
This is why eating before or while drinking makes such a noticeable difference. Food in your stomach, especially protein and fat, slows gastric emptying and delays absorption. Drinking on an empty stomach does the opposite: alcohol passes quickly into the small intestine and blood alcohol concentration (BAC) rises sharply. Carbonated drinks can speed up gastric emptying slightly, which is one reason champagne sometimes feels like it hits faster than still wine with the same alcohol content.
What Alcohol Does to Your Brain
Your brain runs on a balance between excitatory signals (which activate neurons) and inhibitory signals (which quiet them down). Alcohol disrupts this balance in two ways at once. It boosts the activity of GABA, your brain’s primary inhibitory chemical, by binding to GABA receptors and making them more responsive. At the same time, it suppresses glutamate, the brain’s main excitatory chemical, by blocking NMDA receptors. The net result is a brain that’s firing less than normal, which is why alcohol is classified as a central nervous system depressant.
This dual action explains the familiar progression of drinking. At low doses, reduced inhibitory control in the prefrontal cortex produces relaxation, lowered social anxiety, and a sense of disinhibition. As doses increase, the suppression spreads to areas controlling coordination, speech, reaction time, and eventually consciousness. The combination of amplified inhibition and dampened excitation at high levels is what causes “blackout” episodes, where the brain temporarily loses its ability to form new memories.
The Reward System and Why Alcohol Feels Good
Beyond simply slowing your brain down, alcohol also activates reward circuitry that makes the experience feel pleasurable. Alcohol triggers dopamine signals from the ventral tegmental area, a small cluster of neurons in the midbrain, to the nucleus accumbens, a region central to processing reward. Opioid receptors in this same area also become activated during intoxication, which likely accounts for some of the warm, euphoric feeling of early drinks.
Dopamine’s role here is less about pleasure itself and more about learning. It teaches your brain to associate the people, places, and situations around drinking with the rewarding effects of alcohol. Over time, these associations become powerful cues that can trigger cravings. This is the same reward pathway that responds to food, sex, and social connection, and it’s the mechanism that makes alcohol potentially habit-forming. With chronic heavy drinking, the brain adapts by dialing down its own dopamine and GABA activity, which is why regular drinkers need more alcohol to feel the same effect and why withdrawal can produce anxiety, agitation, and in severe cases, seizures.
How Your Body Breaks Alcohol Down
Most alcohol is processed in the liver through a two-step enzymatic pathway. In the first step, an enzyme called alcohol dehydrogenase converts ethanol into acetaldehyde, a highly toxic compound and known carcinogen. In the second step, another enzyme, aldehyde dehydrogenase, quickly converts acetaldehyde into acetate, a far less harmful substance. Acetate is then broken down into water and carbon dioxide in tissues throughout the body and eliminated.
The average person metabolizes roughly one standard drink per hour, equivalent to about 7 grams of alcohol. This rate is relatively fixed. Your liver can only process so much at a time, which is why drinking faster than one drink per hour causes BAC to climb. Coffee, cold showers, and exercise do nothing to speed up this process. Only time clears alcohol from your system.
BAC Levels and Their Effects
Blood alcohol concentration is measured as a percentage of alcohol in your blood, and even small changes produce distinct effects:
- 0.02%: Altered mood, slight relaxation, mild loss of judgment. Most people barely notice this level.
- 0.05%: Lowered alertness, reduced inhibition, impaired judgment. You feel noticeably loosened up.
- 0.08%: Reduced muscle coordination, difficulty detecting danger, impaired reasoning. This is the legal driving limit in most U.S. states.
- 0.10%: Slowed reaction time, slurred speech, sluggish thinking.
- 0.15% to 0.30%: Confusion, vomiting, drowsiness. Motor control is severely compromised.
- 0.30% to 0.40%: Risk of alcohol poisoning and loss of consciousness. This range can be fatal.
These numbers vary based on body weight, sex, tolerance, and how quickly you drank, but the progression is consistent. The brain regions affected follow a predictable order: higher-level judgment and social restraint go first, followed by coordination and speech, then basic functions like consciousness and breathing.
Why Hangovers Happen
Hangovers are not simply dehydration, though that plays a role. The primary driver appears to be an inflammatory response triggered by alcohol and its breakdown products. When your liver converts ethanol to acetaldehyde, the process generates reactive oxygen species, which are harmful molecules that cause oxidative stress. The body recognizes these byproducts as threats and mounts an immune response, flooding the bloodstream with inflammatory signaling molecules.
Research published in the Journal of Clinical Medicine found that hangover severity correlated strongly with blood levels of specific inflammatory markers, particularly interleukin-6, tumor necrosis factor-alpha, and C-reactive protein. Notably, blood ethanol concentration itself (not acetaldehyde) was directly associated with elevated inflammation four hours after drinking, suggesting that ethanol triggers inflammation on its own, independent of its toxic byproducts.
The rate at which your body metabolizes alcohol turns out to be a key factor. People who eliminate ethanol more slowly have more of it lingering in their system through the night and into the next morning. That prolonged exposure generates more oxidative stress and a stronger inflammatory response, resulting in worse hangovers. This is also why darker liquors like bourbon and red wine, which contain higher levels of congeners (fermentation byproducts), tend to produce more severe hangovers. Those additional compounds create extra work for your liver and more inflammatory byproducts.
Why Alcohol Affects People Differently
Genetics play a significant role in how your body handles alcohol. The most well-documented example is the alcohol flush response, which affects nearly 540 million people worldwide, predominantly those of East Asian descent. People with this trait carry an inactive variant of the aldehyde dehydrogenase enzyme (the one responsible for the second step of alcohol metabolism). Because the enzyme doesn’t work properly, acetaldehyde accumulates in the body instead of being quickly converted to harmless acetate. That buildup of toxic acetaldehyde is what causes facial flushing, rapid heartbeat, nausea, and headache, sometimes after just a single drink.
Beyond this specific genetic variant, enzyme activity levels vary widely across individuals and populations. Some people naturally produce more alcohol dehydrogenase, meaning they convert ethanol to acetaldehyde faster. Others have more active versions of the second enzyme, clearing acetaldehyde quickly. Body composition matters too: alcohol is water-soluble, so people with more body water (generally those with larger frames or more muscle mass) dilute alcohol more effectively, resulting in lower BAC from the same amount of alcohol. Women typically reach higher BAC than men of the same weight from identical drinks, partly due to differences in body water percentage and partly due to lower levels of alcohol dehydrogenase in the stomach lining.
Tolerance adds another layer. Regular drinkers develop both metabolic tolerance (the liver becomes slightly more efficient at processing alcohol) and functional tolerance (the brain adapts to operating under alcohol’s influence). Neither form of tolerance reduces the long-term damage alcohol causes to the liver, heart, or brain. It simply means the subjective feeling of intoxication diminishes, which often leads people to drink more to achieve the same effect.