You had a few drinks last night, but today the headache, nausea, and fatigue won’t quit. Why does it feel worse than usual? A hangover is your body’s reaction to alcohol’s toxic byproducts and the dehydration, inflammation, and sleep disruption it causes. How long it lasts and how bad it gets depends on several factors that are within your control and others that are not.
What Causes a Hangover?
Alcohol does not simply leave your body the way water does. Your liver breaks it down in two steps. First, an enzyme called alcohol dehydrogenase turns alcohol into acetaldehyde. Acetaldehyde is a toxic chemical that damages cells and causes inflammation. That is a major reason you feel sick. Second, another enzyme breaks acetaldehyde into acetate, which your body can use for energy.
When you drink faster than your liver can process, acetaldehyde builds up. This buildup triggers headache, nausea, sweating, and a rapid heart rate. Alcohol also dehydrates you by blocking a hormone that normally keeps water in your body. Dehydration alone can cause headache, dizziness, and dry mouth. On top of that, alcohol irritates your stomach lining, disrupts your sleep, and causes blood sugar to drop. Each of these effects contributes to hangover symptoms.
Why Does My Hangover Feel Worse This Time?
Hangover severity varies from person to person and from one drinking session to the next. Several factors explain why one night of drinking leaves you wrecked while another does not.
How much you drank. The more alcohol you consume, the higher the acetaldehyde spike and the greater the dehydration. But even the same amount of alcohol can hit you harder depending on how fast you drank, whether you ate, and what you mixed it with.
Your sleep quality. Alcohol interferes with REM sleep and deep sleep. You may have slept for eight hours but gotten very little restorative sleep. That adds to fatigue and brain fog the next day.
Your hydration status before drinking. If you started the evening already dehydrated, the effect multiplies.
Your genetics. Some people have genetic variations that slow down the breakdown of acetaldehyde. People of East Asian descent, for example, more commonly carry a variant of the ALDH2 enzyme that processes acetaldehyde poorly. This leads to flushing, rapid heart rate, and more intense hangovers with smaller amounts of alcohol.
Your age. As you get older, your liver metabolizes alcohol more slowly, and your body’s ability to handle inflammation and dehydration declines. A hangover that barely phased you at 25 can floor you at 45.
Other substances. Combining alcohol with other drugs, including over-the-counter medications, can worsen hangover symptoms. Certain medications like antihistamines or antidepressants alter how your body processes alcohol.
How Much Alcohol Causes a Hangover?
There is no single number. Most people will experience a hangover after reaching a blood alcohol concentration of 0.10% or higher, which is above the legal driving limit of 0.08% in most US states. For a 150-pound person, that typically means four to five standard drinks within two hours if they have not eaten. But sensitivity varies widely.
The only way to guarantee no hangover is to drink no alcohol. However, keeping your intake below one drink per hour and staying well hydrated reduces your risk. A standard drink is defined as 12 ounces of beer at 5% alcohol, 5 ounces of wine at 12% alcohol, or 1.5 ounces of distilled spirits at 40% alcohol.
Why Am I Still Hungover After One Drink?
Some people feel hungover after a single drink. This can happen for several reasons. One possibility is a genetic condition called alcohol intolerance, where the body lacks the enzyme to properly break down acetaldehyde. Even one drink can cause flushing, headache, nausea, and fatigue that look very much like a hangover.
Another possibility is that you are reacting to something else in the drink. Congeners are substances produced during fermentation that give drinks their flavor and color. Darker drinks like whiskey, red wine, and brandy contain more congeners than clear drinks like vodka or gin. Some people are sensitive to congeners and develop headache and nausea after just one serving.
It is also possible that your symptoms are not a hangover at all. Dehydration from a long day, poor sleep, or an illness can mimic hangover symptoms. If you consistently feel sick after small amounts of alcohol, it is worth discussing with a healthcare provider.
What Actually Helps a Hangover?
There is no cure for a hangover. Once alcohol is in your system, your body must process it. No pill, drink, or food will speed that up. However, you can manage symptoms and make the experience less miserable.
Time. On average, your liver processes about one standard drink per hour. A hangover resolves as acetaldehyde clears and your body rehydrates. That usually takes several hours to a full day, depending on how much you drank.
Water. Rehydration helps with headache and fatigue. Drink water steadily. Electrolyte drinks may help, but plain water is sufficient if you eat a meal with salt.
Food. Eating a bland meal can settle your stomach and help stabilize your blood sugar. Crackers, toast, or rice work well. Avoid greasy food — it can worsen nausea.
Sleep. Rest as much as you can. Your body needs time to recover from the sleep disruption alcohol caused.
Pain relievers. Ibuprofen or naproxen can help with headache and muscle aches. Avoid taking acetaminophen (Tylenol) for at least 24 hours after heavy drinking because your liver is already stressed processing alcohol, and acetaminophen can cause liver damage when combined with alcohol.
What does not help. Drinking more alcohol the next morning — often called “hair of the dog” — delays the hangover. It does not cure it. Caffeine can briefly reduce fatigue but can also worsen dehydration and anxiety. There is no high-quality evidence that any supplement, including vitamin B, milk thistle, or prickly pear, reliably prevents or treats hangovers.
Does the Type of Alcohol Matter?
Yes. The concentration of congeners varies by drink. Dark liquors like bourbon, whiskey, and dark rum have significantly more congeners than clear liquors like vodka and gin. Red wine and beer also contain congeners in varying amounts.
Studies show that people who drink dark liquors tend to report more severe hangovers than those who drink clear liquors, even when the total alcohol consumed is the same. If you are prone to bad hangovers, choosing a drink with fewer congeners may help, but it is not a guarantee. The amount of alcohol you drink matters more than the type.
When Should I Worry About Hangover Symptoms?
Most hangovers are unpleasant but not dangerous. However, some symptoms can signal a more serious problem. If you or someone else has any of the following, seek medical attention immediately:
- Confusion, difficulty staying awake, or inability to wake up
- Slow or irregular breathing (fewer than 8 breaths per minute)
- Cold, clammy, or pale skin
- Repeated vomiting
- Seizures
These can be signs of alcohol poisoning, which is a medical emergency. Alcohol poisoning happens when a high concentration of alcohol in the blood suppresses vital functions like breathing and heart rate. It can be fatal. Do not assume someone who is unconscious is “just sleeping it off.”
Also consider whether your hangover symptoms could be due to another condition. If you consistently get severe headaches after drinking, you may have a migraine triggered by alcohol. If you experience flushing, wheezing, or hives, you may have an alcohol allergy or intolerance. A healthcare provider can help distinguish these.
Frequently Asked Questions
Can I prevent a hangover before drinking?
Eating a meal before drinking, staying hydrated, and limiting your intake to one drink per hour can reduce your risk. No method guarantees prevention because your liver can only process so much alcohol per hour.
Does drinking water between alcoholic drinks help?
Yes, drinking water between drinks helps slow your overall alcohol consumption and reduces dehydration. It does not speed up alcohol metabolism, but it can lessen hangover severity.
How long does a hangover last?
Most hangovers resolve within 12 to 24 hours after your last drink. Symptoms peak when your blood alcohol level returns to zero, typically several hours after you stop drinking.
Is it safe to take pain relievers before drinking to prevent a hangover?
No. Taking acetaminophen or ibuprofen before drinking does not prevent a hangover and can increase your risk of liver or stomach damage. Take pain relievers only after drinking and only if you have a real need, and avoid acetaminophen for 24 hours after heavy drinking.
