Being hungover means you’re experiencing the physical and mental aftereffects of drinking too much alcohol. Researchers define an alcohol hangover as the combination of negative mental and physical symptoms that follow a single episode of alcohol consumption, starting when your blood alcohol level drops back toward zero. In practical terms, it’s the headache, nausea, fatigue, and foggy thinking you feel the morning after a night of heavy drinking.
What a Hangover Feels Like
The classic hangover is a package of symptoms, not just one. The physical side typically includes headache, nausea, fatigue, sensitivity to light and sound, diarrhea, and a general feeling of being unwell. Most people also experience thirst and dry mouth. But hangovers aren’t purely physical. You may also feel irritable, anxious, or unable to concentrate. Some people describe a vague sense of dread or low mood that lingers alongside the physical discomfort.
The mental effects are more significant than many people realize. Lab studies show that hungover people make substantially more errors on tasks involving working memory, attention, and goal-directed thinking compared to when they’re sober. Reaction times slow, and the ability to switch between tasks drops. These cognitive effects can be large enough to meaningfully impair driving, work performance, and decision-making, even though no alcohol remains in your system.
Why Your Body Feels This Way
There’s no single cause of a hangover. Several overlapping processes kick in as your body processes alcohol, and together they produce that miserable morning-after feeling.
Dehydration and fluid loss. Alcohol suppresses a hormone called vasopressin, which normally tells your kidneys to hold onto water. When vasopressin drops, your kidneys let more fluid pass through as urine. This is why you urinate so frequently while drinking. The result is dehydration, which contributes to headache, thirst, dizziness, and fatigue. Alcohol also depletes key electrolytes, particularly sodium, magnesium, and potassium. Sodium imbalance is the most common electrolyte disruption from heavy drinking, and nearly half of heavy drinkers show low potassium levels.
Inflammation. Alcohol triggers your immune system in ways that resemble a mild illness. Studies have found that during a hangover, levels of specific immune signaling molecules rise significantly compared to normal conditions. These inflammatory signals are linked to the nausea, headache, diarrhea, and fatigue you feel. In other words, part of a hangover is your own immune system overreacting to what alcohol did to your body.
Alcohol metabolism byproducts. Your liver breaks alcohol down in stages. One intermediate product, acetaldehyde, is toxic and was long blamed for hangover symptoms. The picture is more nuanced than that. Acetaldehyde doesn’t easily cross into the brain, so it likely doesn’t cause hangover symptoms directly. However, it does contribute to oxidative stress, a kind of cellular damage that fuels the inflammatory response. Research shows that the strongest predictor of hangover severity is simply how much alcohol you consumed, not how much acetaldehyde built up in your blood.
How Long a Hangover Lasts
Hangover symptoms peak when your blood alcohol concentration returns to roughly zero. For most people, that’s somewhere between 12 and 16 hours after they stopped drinking. Symptoms can last 24 hours or longer, depending on how much you drank, your body size, how well you slept, and whether you ate before or during drinking.
The timeline typically looks like this: you wake up feeling rough, symptoms intensify through the morning, and they gradually fade over the course of the day. Some people bounce back by the afternoon. Others feel off well into the next evening, especially after particularly heavy drinking.
Why Some Nights Hit Harder
Not every drinking session produces the same hangover, and several factors explain the difference.
Type of alcohol. Different drinks contain different levels of congeners, which are chemical byproducts of fermentation. Dark liquors like bourbon, brandy, cognac, and red wine tend to be high in congeners. Tequila is also high in congeners despite being relatively light in color. Clear drinks like vodka, gin, white wine, light rum, sake, and light beer contain fewer congeners and are generally associated with milder hangovers.
How much and how fast. Total alcohol consumed is the single biggest factor. Drinking quickly on an empty stomach means higher peak blood alcohol levels, which means a worse hangover. Eating before or while drinking slows alcohol absorption and blunts the peak.
Sleep disruption. Alcohol fragments sleep even if you fall asleep quickly. You spend less time in the deeper, restorative stages of sleep. Poor sleep quality amplifies fatigue, irritability, and cognitive impairment the next day, layering on top of the hangover itself.
Individual biology. Genetics play a role in how efficiently your liver processes alcohol. People whose bodies clear alcohol and its byproducts more slowly tend to have worse hangovers. Body weight, sex, hydration status before drinking, and even your mood while drinking all influence the outcome.
What Actually Helps (and What Doesn’t)
No product has been proven to cure a hangover. The FDA has sent warning letters to companies marketing supplements as hangover cures, noting that these products have not been evaluated for safety or effectiveness. Any supplement claiming to prevent or cure hangovers is making an unapproved medical claim.
What does help is straightforward. Drinking water or electrolyte-containing beverages helps correct dehydration and mineral losses. Eating bland, easy-to-digest food gives your body fuel to recover. Over-the-counter pain relievers can take the edge off a headache, though aspirin and ibuprofen can irritate an already-upset stomach. Rest and time are the most reliable remedies. Your body needs to clear the remaining byproducts, resolve the inflammation, and restore its fluid balance, and that simply takes hours.
The “hair of the dog” approach, drinking more alcohol to ease symptoms, only delays the inevitable. It temporarily masks symptoms by reintroducing alcohol, but the hangover returns once that new dose wears off, often worse than before.