Alcohol works by slowing down your brain’s signaling system, boosting the activity of your brain’s main “brake” chemical while suppressing its main “gas pedal” chemical. That shift is what produces the familiar feelings of relaxation, lowered inhibitions, and impaired coordination. But the full picture involves much more than just your brain. From the moment you take a sip, your body launches a complex chain of absorption, neurochemical changes, and metabolic processing that explains everything from the initial buzz to the next-morning hangover.
How Alcohol Gets Into Your Blood
Alcohol is absorbed slowly through the stomach and rapidly through the small intestine. The speed at which your stomach empties its contents into the small intestine is the single biggest factor controlling how fast alcohol hits your bloodstream. When your stomach empties quickly, absorption is fast and your blood alcohol level spikes higher. When it empties slowly, absorption is delayed and peak blood alcohol levels are lower.
This is why eating before or while drinking makes such a noticeable difference. Food slows gastric emptying, which means alcohol trickles into your small intestine gradually instead of flooding it all at once. Drinking on an empty stomach does the opposite, letting alcohol pass quickly into the intestine and producing a faster, stronger effect. Carbonation, the type of food in your stomach, and even stress levels can all shift gastric emptying speed, which is part of why the same number of drinks can hit you differently on different nights.
What Alcohol Does in Your Brain
Once alcohol reaches your brain, it acts on several neurotransmitter systems simultaneously. The most important interaction is with GABA, your brain’s primary inhibitory signaling chemical. GABA receptors are chloride ion channels that, when activated, slow down nerve cell firing. Alcohol enhances GABA’s effects in multiple ways: it increases the amount of GABA released by nerve cells, makes receptors more sensitive to GABA, and boosts levels of naturally occurring brain steroids that further amplify GABA signaling. The net result is a widespread dampening of brain activity, which is why alcohol makes you feel relaxed, less anxious, and less coordinated.
At the same time, alcohol suppresses your brain’s main excitatory system. Glutamate receptors normally keep your brain alert and responsive, but alcohol blocks their activity. This one-two punch of enhancing inhibition and reducing excitation is what makes alcohol a depressant in the pharmacological sense. It’s not that alcohol makes you emotionally depressed; it depresses (slows) neural activity across the brain.
Alcohol also triggers dopamine release in your brain’s reward circuit, a pathway that runs from deep in the midbrain to areas involved in motivation and pleasure. Both alcohol itself and its metabolic byproducts can increase the firing rate of dopamine neurons in this circuit, which creates the pleasurable, reinforcing feeling that makes you want to keep drinking. This same reward pathway responds to food, sex, and other drugs of abuse, which is a key reason alcohol carries addiction potential.
Beyond GABA, glutamate, and dopamine, alcohol also activates serotonin receptors. Serotonin receptor activation on inhibitory nerve cells can further increase GABA release, compounding the sedative effect. It also contributes to additional dopamine and glutamate release, adding to the complex cocktail of neurochemical changes behind intoxication.
How Your Body Breaks Down Alcohol
Your liver handles the vast majority of alcohol processing through a two-step enzymatic pathway. In the first step, an enzyme converts ethanol into acetaldehyde, a highly toxic compound and known carcinogen. Acetaldehyde is responsible for many of alcohol’s harmful effects, but it’s typically short-lived. A second enzyme quickly converts acetaldehyde into acetate, a much less toxic substance. Acetate is then broken down into water and carbon dioxide in tissues throughout the body and easily eliminated.
The liver clears alcohol from the blood at a relatively fixed rate, roughly 15 mg per 100 ml of blood per hour. This rate varies somewhat between individuals and drinking occasions, but it can’t be meaningfully sped up by coffee, cold showers, or food after the fact. If you drink faster than your liver can process, alcohol accumulates in your blood and intoxication increases. Blood alcohol concentration can range from 0% to over 0.4%, a level that can be fatal.
Why Alcohol Affects People Differently
Body composition plays a major role. Women generally have proportionally more body fat and less body water than men at the same weight. Because alcohol disperses in water, women reach higher peak blood alcohol levels than men after consuming equivalent amounts, even when the dose is adjusted for body weight. In studies where doses were calculated based on total body water instead of body weight, this gender difference disappeared entirely.
Enzyme activity also differs. Women may have lower rates of a “first pass” metabolism in the stomach and liver, meaning more alcohol reaches the bloodstream intact. Interestingly, women tend to have a larger liver volume relative to lean body mass, about 38% higher than men, which partially compensates by allowing faster overall processing once alcohol is in the liver. Male hormones appear to inhibit one of the key liver enzymes involved in alcohol breakdown, which may slow processing in men.
How Alcohol Disrupts Sleep
Alcohol acts as a sedative that initially makes you fall asleep faster and spend more time in deep sleep during the first half of the night. This is why a nightcap can feel like it helps. But the second half of the night tells a different story. As your body processes the alcohol, sleep becomes fragmented, with more wakefulness and lighter sleep stages.
REM sleep, the phase critical for memory consolidation and emotional processing, takes a particular hit. Alcohol delays the onset of REM sleep and reduces the total amount of it, sometimes across the entire night. The mechanism likely involves alcohol’s enhancement of GABA activity, which suppresses the brain processes that normally initiate REM cycles. The result is that even after a full night in bed, you wake up less rested than you would have without drinking.
What Actually Causes a Hangover
Hangovers are more complex than simple dehydration. Two major biological processes drive hangover symptoms: alcohol metabolism and immune system activation.
When your liver converts ethanol to acetaldehyde, the process generates reactive oxygen species, unstable molecules that damage cells and trigger oxidative stress. Acetaldehyde also combines with other byproducts to form compounds that the body recognizes as foreign. This triggers a genuine inflammatory immune response, complete with elevated levels of the same inflammatory markers you’d see during an infection.
Research has found that hangover severity correlates directly with blood levels of specific inflammatory signals, including interleukin-6, tumor necrosis factor-alpha, and C-reactive protein. Notably, it’s the ethanol itself, not just acetaldehyde, that drives much of this inflammation. Blood ethanol levels four hours after drinking were positively associated with inflammatory marker elevations, suggesting a direct inflammatory effect. Oxidative stress markers also correlate with how bad the hangover feels.
The timing matters too. When your body is slow to eliminate ethanol in the first hours after drinking, more alcohol remains in your system during the second half of the night and into the morning. This prolongs oxidative stress and strengthens the inflammatory response, producing a worse hangover. This explains why drinking heavily late at night, when your body has less time to process before morning, tends to produce especially rough mornings.
Why Tolerance Develops
With repeated drinking, your brain adapts to alcohol’s presence by rebalancing its neurochemistry. Chronic alcohol exposure causes your brain to dial up the excitatory glutamate system and dial down the inhibitory GABA system. In practical terms, your brain becomes less responsive to alcohol’s sedative effects, so you need more drinks to feel the same level of intoxication.
This adaptation is also why sudden withdrawal from heavy drinking can be dangerous. The brain has compensated for alcohol’s depressant effects by running its excitatory systems at a higher baseline. Remove the alcohol, and those overactive excitatory systems are suddenly unopposed, which can cause anxiety, tremors, seizures, and other withdrawal symptoms. The same neurochemical rebalancing that creates tolerance is what makes physical dependence possible.