When you drink alcohol, it enters your bloodstream within minutes and triggers a cascade of changes across nearly every system in your body. Your liver starts breaking it down, your brain chemistry shifts, your heart rate rises, and your digestive tract takes a hit. Here’s what actually happens, from the first sip to the morning after.
How Your Body Breaks Down Alcohol
About 20% of the alcohol you drink is absorbed through your stomach lining. The rest passes into your small intestine, where it enters the bloodstream quickly. From there, most of it travels to your liver for processing.
Your liver handles alcohol in two steps. First, an enzyme converts the alcohol into a compound called acetaldehyde, which is highly toxic and a known carcinogen. Fortunately, acetaldehyde is short-lived. A second enzyme rapidly converts it into acetate, a much less harmful substance that your body then breaks down into water and carbon dioxide for easy elimination. The entire process is limited by how fast your liver can work, which is roughly one standard drink per hour. Anything beyond that stays circulating in your blood, which is why drinking faster than your liver can keep up is what gets you drunk.
What Happens in Your Brain
Alcohol doesn’t just slow you down in a general way. It targets specific chemical messaging systems in your brain. It boosts the activity of your brain’s main “calm down” signal while suppressing its main “stay alert” signal. The result is that initial wave of relaxation, lowered inhibitions, and the warm, social feeling many people associate with a first drink. At the same time, alcohol triggers a release of your brain’s reward chemical, which is what makes drinking feel pleasurable and reinforces the desire to keep going.
As your blood alcohol level rises, these effects intensify and become less pleasant. The shift from “relaxed and social” to “clumsy and confused” happens on a surprisingly predictable scale.
How Impairment Builds With Each Drink
Blood alcohol concentration (BAC) is measured as a percentage, and even small increases produce measurable changes in how you think and move. Data from the National Highway Traffic Safety Administration lays out the progression:
- BAC 0.02 (about one drink): Slight mood change, some loss of judgment, mild body warmth. Your ability to track moving objects and divide your attention between two tasks starts to decline.
- BAC 0.05 (two to three drinks): Exaggerated behavior, lowered alertness, release of inhibitions. Small-muscle control starts to slip, including your ability to focus your eyes. Coordination drops noticeably.
- BAC 0.08 (three to four drinks): This is the legal driving limit in most U.S. states. Balance, speech, vision, and reaction time are all impaired. Short-term memory, self-control, and reasoning suffer. You become worse at detecting danger.
- BAC 0.10: Clear deterioration in reaction time. Slurred speech, poor coordination, slowed thinking.
- BAC 0.15: Far less muscle control than normal. Significant loss of balance. Vomiting may occur, especially if you reached this level quickly.
These thresholds apply to an average person. Your actual experience depends on your body size, biological sex, how much you’ve eaten, and how quickly you’re drinking.
Why Alcohol Hits Women Harder
Women consistently reach higher blood alcohol levels than men after drinking the same amount, even when researchers adjust for body weight. The main reason is body composition: women typically carry proportionally more body fat and less water than men of similar weight, and alcohol disperses in water. Less water means the same amount of alcohol becomes more concentrated. In one study, the BAC difference between men and women disappeared entirely when researchers gave doses based on total body water instead of body weight.
Women also appear to have lower levels of the stomach enzyme that begins breaking down alcohol before it reaches the bloodstream, so more alcohol enters circulation intact. On the flip side, women’s livers are proportionally larger relative to their lean body mass, giving them a faster alcohol elimination rate, roughly 33% higher than men’s. The net effect, though, is that women still feel the same amount of alcohol more intensely.
Effects on Your Heart and Blood Vessels
Your cardiovascular system responds to alcohol almost immediately. In controlled studies, a single dose of alcohol raised heart rate by about 6 beats per minute on average while also reducing the heart’s stroke volume, meaning each beat pumped slightly less blood. Heart rate variability dropped as well, a sign that the nervous system’s fine-tuned control over your heart rhythm was disrupted.
The effect on blood pressure is surprisingly complicated. Alcohol triggers competing signals: some push blood vessels to dilate, others cause constriction. These opposing forces often cancel each other out in the short term, which is why blood pressure may not change much after a single drinking session. Over time, however, chronic heavy drinking is strongly linked to high blood pressure and heart disease.
What Alcohol Does to Your Gut
Alcohol is an irritant from the moment it enters your mouth. As it travels down through the esophagus and into the stomach, it increases the risk of cancers along that entire path. In the stomach, it can inflame the lining and increase acid production, which is why drinking on an empty stomach so often leads to nausea.
In the small intestine, alcohol interferes with the absorption of essential nutrients. Chronic drinking impairs your body’s ability to absorb glucose, amino acids, and several key vitamins and minerals, including thiamine (B1), riboflavin (B2), folate (B9), vitamin C, zinc, selenium, and iron. This is one reason long-term heavy drinkers frequently develop nutritional deficiencies even when their diet is adequate. The damage to nutrient absorption is a significant contributor to the malnutrition often seen in people with alcohol use disorder.
How Alcohol Wrecks Your Sleep
Alcohol makes you fall asleep faster, which gives the false impression that it’s a sleep aid. What actually happens is more disruptive. In the first half of the night, alcohol promotes deep sleep while suppressing REM sleep, the stage critical for memory consolidation and emotional processing. Then, in the second half of the night, the pattern flips: deep sleep drops off and you’re more likely to wake up repeatedly. Overall sleep efficiency suffers, and you spend more time awake after initially falling asleep.
This is why even moderate drinking before bed leaves you feeling unrested the next day, regardless of how many hours you technically spent in bed.
What Causes a Hangover
Hangovers are not caused by any single mechanism. Several processes contribute, and they interact in ways researchers are still untangling. The toxic intermediate acetaldehyde plays a role, but it’s not the whole story. Your immune system mounts an inflammatory response to alcohol, producing molecules that cause the headache, fatigue, and general malaise you feel the next morning. Alcohol also generates oxidative stress, a form of cellular damage from unstable molecules.
Interestingly, the speed of your metabolism matters. People who eliminate alcohol from their blood more slowly tend to have worse hangovers, likely because ethanol itself (unlike acetaldehyde) can cross into the brain. The longer it lingers, the more damage it does. Oxidative stress that peaks later in the process, hours after you’ve stopped drinking, correlates with more severe next-day symptoms.
Dehydration contributes too. Alcohol suppresses the hormone that tells your kidneys to retain water, which is why you urinate more frequently while drinking. But dehydration alone doesn’t fully explain hangover severity, which is why simply drinking water between alcoholic beverages helps but doesn’t prevent a hangover entirely.
Long-Term Risks of Regular Drinking
Excessive alcohol use causes roughly 178,000 deaths per year in the United States, a number that increased 29% compared to estimates from just a few years earlier. About two-thirds of those deaths, around 117,000, result from chronic conditions that develop over years of drinking: liver disease, several types of cancer, heart disease, and alcohol use disorder.
The CDC defines moderate drinking as two drinks or fewer per day for men and one drink or fewer per day for women. Consistently exceeding those amounts raises your risk for all of the conditions above. The cancer risk is particularly important to understand because it exists at any level of regular drinking, not just heavy use. Alcohol’s toxic metabolite, acetaldehyde, is a confirmed carcinogen, and it damages DNA in the tissues it contacts most directly: the mouth, throat, esophagus, and liver.