The substance in alcohol that makes you drunk is ethanol, a small molecule produced by fermenting sugars. Whether you’re drinking beer, wine, or spirits, ethanol is the only psychoactive ingredient they share. It’s classified as a central nervous system depressant, meaning it slows brain activity rather than speeding it up, even though those first couple of drinks can feel energizing.
How Ethanol Gets Into Your Blood
When you take a drink, only about 20% of the ethanol is absorbed through your stomach lining. The remaining 80% passes into your small intestine, which has a much larger surface area and absorbs it quickly into your bloodstream. From there, ethanol circulates to your brain within minutes.
How fast you hit peak intoxication depends partly on what you’re drinking. In studies where people drank on an empty stomach, vodka mixed with tonic water produced peak blood alcohol levels in roughly 36 minutes. Wine took about 54 minutes, and beer took around 62 minutes. Eating before or while drinking slows absorption further because food delays how quickly alcohol moves from your stomach to your small intestine.
What Ethanol Does to Your Brain
Ethanol doesn’t just flip one switch. It changes the activity of multiple brain signaling systems at once, which is why being drunk affects your mood, coordination, memory, and judgment all at the same time.
The biggest effect involves your brain’s main braking system. Your brain uses an inhibitory chemical called GABA to calm neural activity. Ethanol amplifies GABA’s effects dramatically. In laboratory measurements, ethanol increased the flow of charged particles through GABA-controlled channels by as much as 260%. The channels stay open longer, open more frequently, and spend less time closed. The net result is that your brain’s ability to fire signals gets dialed way down, producing the sedation, relaxation, and slowed reflexes you feel when drunk.
At the same time, ethanol suppresses your brain’s main excitatory system. A receptor called the NMDA receptor normally helps neurons communicate quickly and form new memories. Ethanol blocks this receptor’s function, which is why alcohol impairs memory so effectively. This is the mechanism behind blackouts: ethanol prevents the brain region responsible for forming new memories from doing its job. In animal studies, ethanol cut fear-based learning nearly in half compared to controls.
Why Drinking Feels Good at First
If ethanol is a depressant, why do the first few drinks feel pleasurable and even stimulating? The answer is dopamine. Ethanol triggers dopamine release in the brain’s reward center, the same circuit activated by food, sex, and other pleasurable experiences. At low concentrations, ethanol boosts the firing rate of specific neurons in this reward area, increasing dopamine signaling. This creates the initial buzz, the loosened inhibitions, and the warm social feeling people associate with a couple of drinks.
At higher doses, the depressant effects overwhelm the dopamine boost. The sedation, slurred speech, and loss of coordination take over. This is also why chasing that early euphoria by drinking more rarely works. The reward signal fades while the impairing effects keep building.
How Coordination Falls Apart
The stumbling and slurred speech that come with heavier drinking trace back to ethanol’s effect on the cerebellum, the brain region that coordinates movement and balance. Ethanol increases inhibitory GABA signaling throughout the cerebellum, not just in one cell type but across multiple layers of the circuit. It simultaneously reduces excitatory signaling by blocking glutamate release. The combined effect weakens the output signals the cerebellum sends to the rest of the brain, producing what researchers call cerebellar ataxia: impaired balance, clumsy hand movements, and difficulty with precise motor tasks like speaking clearly.
What Intoxication Looks Like at Each Level
Blood alcohol concentration (BAC) is measured as a percentage of alcohol in your blood. The National Highway Traffic Safety Administration outlines a general progression of impairment:
- 0.02%: Slight relaxation, mild mood change, some loss of judgment. You may already have trouble tracking moving objects.
- 0.05%: Lowered alertness, exaggerated behavior, reduced coordination. Inhibitions start to loosen noticeably.
- 0.08%: This is the legal driving limit in most U.S. states. Balance, speech, vision, and reaction time are all measurably impaired. Short-term memory starts to suffer.
- 0.10%: Clear deterioration in reaction time. Slurred speech and poor coordination are obvious to others.
- 0.15%: Significant loss of balance and muscle control. Vomiting is common unless tolerance has built up over time.
How Your Body Breaks Ethanol Down
Your liver does the heavy lifting. An enzyme called alcohol dehydrogenase converts ethanol into acetaldehyde, a toxic byproduct that contributes to hangover symptoms and, over time, can damage DNA and organs. A second enzyme, aldehyde dehydrogenase, then converts acetaldehyde into acetate, which is harmless and eventually broken down into carbon dioxide and water.
This process runs at a relatively fixed speed. Your liver can only clear so much ethanol per hour, which is why drinking faster than your body can metabolize it causes BAC to climb. No amount of coffee, food, or water speeds up this enzyme system once alcohol is in your blood.
Why the Same Drinks Hit People Differently
Body composition is the single biggest reason two people can drink the same amount and feel very different effects. Ethanol dissolves in water, so the more water in your body, the more diluted the alcohol becomes. Women typically have a lower proportion of body water than men of similar weight, which means they reach higher blood alcohol concentrations from the same number of drinks.
Enzyme differences matter too. Women tend to have lower levels of alcohol dehydrogenase in the stomach lining, meaning less ethanol is broken down before it reaches the bloodstream. Once alcohol is in the blood, women show roughly 27% lower elimination rates than men, largely because of differences in liver size and lean body mass. Age also plays a role: older adults generally have less body water than younger adults, amplifying the effect of each drink.
Genetics can change the picture further. Some people, particularly those of East Asian descent, carry a variant of aldehyde dehydrogenase that works slowly. This causes acetaldehyde to build up, producing facial flushing, nausea, and a rapid heartbeat, sometimes after just a small amount of alcohol. The same drink that gives one person a mild buzz can make another person feel genuinely ill.