Being hungover is your body’s reaction to drinking more alcohol than it can comfortably process. Symptoms typically peak right as your blood alcohol level drops back to zero and can persist for 24 hours or longer. What feels like a single miserable experience is actually several biological disruptions happening at once: dehydration, inflammation, poor sleep, and the lingering effects of alcohol on your brain and gut.
What Happens in Your Body
When you drink, your liver breaks alcohol down in stages. First it converts ethanol into a toxic byproduct, then into a harmless substance your body can eliminate. The trouble starts when you drink faster than your liver can keep up. Alcohol circulates through your bloodstream and affects nearly every organ system while your body works to clear it.
One of the most immediate effects is on your kidneys. Alcohol suppresses a hormone called vasopressin (sometimes called antidiuretic hormone), which normally tells your kidneys to hold on to water. With that signal turned down, your kidneys let far more fluid pass through than usual. Early research estimated that every 10 grams of alcohol consumed produces roughly an extra 100 milliliters of urine. That accelerated fluid loss is why you urinate so frequently while drinking, and it sets the stage for the dehydration, thirst, and dizziness you feel the next morning.
Alcohol also triggers a genuine inflammatory response. The day after heavy drinking, blood levels of C-reactive protein and a signaling molecule called interleukin-6 rise significantly. These are the same markers your immune system produces when you’re fighting an infection. That low-grade inflammation contributes to the achiness, fatigue, and general feeling of being unwell that defines a hangover. Saliva concentrations of interleukin-6 nearly doubled in one study comparing a post-drinking day to a control day, which helps explain why a hangover can feel almost like coming down with something.
Why Your Head Pounds and Your Stomach Churns
The headache is likely a combination of dehydration, blood vessel changes, and inflammation in the brain. Interestingly, research suggests that alcohol itself, not its toxic byproduct, is the main driver of hangover severity. That’s because alcohol crosses the blood-brain barrier easily, while its byproduct largely does not. So the duration and intensity of alcohol’s direct contact with brain tissue matters more than how quickly your liver processes the intermediate step.
Nausea and stomach discomfort come from alcohol irritating your stomach lining and increasing acid production. Alcohol also slows the rate at which your stomach empties, which can leave you feeling bloated and queasy well into the next day. On top of that, heavy drinking can pull down levels of key minerals like magnesium, potassium, and sodium. These electrolyte shifts can cause muscle weakness, cramping, and a general sense of shakiness.
Why You Feel Exhausted Despite Sleeping
Alcohol is deceptive when it comes to sleep. It helps you fall asleep faster, but the quality of that sleep is significantly worse. In the first half of the night, alcohol suppresses REM sleep, the stage most associated with mental restoration and dreaming. Your brain essentially skips its most restorative work. Then in the second half of the night, sleep becomes fragmented: you wake more often and spend more time in the lightest stage of sleep.
The result is that even after seven or eight hours in bed, you wake up feeling like you barely slept. This disrupted sleep architecture is a major contributor to the brain fog, irritability, and difficulty concentrating that come with a hangover. It also means that “sleeping it off” doesn’t work as well as you’d expect, because the sleep you’re getting while alcohol is still in your system isn’t doing what normal sleep does.
Genetics Play a Real Role
Not everyone gets hangovers with equal intensity from the same amount of alcohol. One well-studied genetic factor involves a variant in the enzyme responsible for breaking down alcohol’s toxic byproduct. This variant, common in people of East Asian descent, slows that breakdown process considerably. People who carry it tend to experience more severe hangover symptoms at lower amounts of alcohol and are more likely to report hangovers after just a few drinks. If you’ve noticed that you seem to get worse hangovers than friends who drink similar amounts, genetics may genuinely be part of the explanation.
How Long a Hangover Lasts
Hangover symptoms begin as your blood alcohol concentration falls and peak right around the time it hits zero. For most people, that means symptoms are worst the morning after drinking, roughly 12 to 14 hours after their last drink. From there, symptoms gradually improve but can linger for a full 24 hours or longer, depending on how much you drank, how hydrated you were, whether you ate beforehand, and your individual biology.
The timeline tends to follow a pattern: headache and nausea are often worst in the first few hours after waking, while fatigue and difficulty concentrating can drag on through the afternoon and evening. Younger drinkers sometimes assume hangovers get worse with age, and there’s some truth to that. Your liver processes alcohol more slowly as you get older, and your body holds less water, making dehydration hit harder.
Why No Hangover Cure Actually Works
Despite a massive market for hangover remedies, the science is bleak. A review of 82 commercially available hangover products found that none had peer-reviewed human data demonstrating either safety or efficacy. That includes supplements, vitamin blends, herbal formulas, and “detox” drinks. The products that claim to accelerate alcohol metabolism or neutralize its byproducts have not proven those claims in controlled trials.
What does help is straightforward: water, food, electrolytes, and time. Drinking water between alcoholic beverages and before bed won’t prevent a hangover entirely, but it offsets some of the fluid loss. Eating before and during drinking slows alcohol absorption. Over-the-counter pain relievers can address the headache, though be cautious with anything that’s hard on the stomach or liver when combined with alcohol. Beyond that, recovery is mostly a waiting game while your body clears the remaining effects and restores its normal balance.