What is a hangover?

A hangover is when you have unpleasant physical and mental symptoms after drinking too much alcohol.

When does a hangover start?

Hangovers usually begin several hours after you stop drinking. The symptoms can vary in intensity, depending on the person and the type and amount of alcohol consumed.

How much alcohol causes a hangover?

Having more than one drink per hour can cause problems. Your body needs about an hour to metabolize, or process, one drink, which is:

  • 12 ounces of regular or light beer — about one can (5% alcohol).
  • 8 to 9 ounces of malt liquor or many types of craft beers — approximately half a pint glass (7% alcohol).
  • 5 ounces of table wine — about one glass (12% alcohol).
  • 1.5 ounces of liquor — approximately one shot (40% alcohol).

How common are hangovers?

Hangovers are very common in people who consume too much alcohol. In one study, researchers found that about 75% of people who drank excessively the night before reported hangover symptoms. The researchers concluded that 25% to 30% of people who drink may be resistant to hangovers.

What causes a hangover?

Alcohol causes hangovers — but it’s not simple. Drinking affects your body in several ways:

Direct effects of alcohol

  • Dehydration: Alcohol is a diuretic. It causes you to pee more, so you lose a lot of fluid. (You can lose up to a quart of urine in the hours after having four drinks.) Alcohol also reduces the release of the hormone vasopressin. This hormone balances your body’s fluids. Dehydration causes thirst, fatigue and headaches.
  • Electrolyte imbalance: Your body needs certain chemicals, called electrolytes, to perform at its best. Passing large amounts of urine throws electrolytes out of balance.
  • Gastrointestinal problems: Alcohol irritates the lining of your stomach and intestines. It slows the rate of digestion, increasing fatty substances in your liver and stomach and pancreas secretions. All these processes lead to an upset stomach and nausea.
  • Inflammation: Alcohol increases inflammation throughout your body. It can contribute to the general unwell feeling of a hangover.
  • Low blood sugar: This effect usually happens in people who have alcohol use disorder. They may binge drink and fail to eat properly over a few days. As the body processes alcohol, it produces lactic acid. Lactic acid reduces blood sugar production, resulting in fatigue, sweating, hunger and shakiness.
  • Disruption of sleep and other processes: While alcohol is a sedative and can promote sleep, hangover symptoms usually interfere with sleep. You may have insomnia as your blood alcohol levels get lower, so you feel fatigued. Alcohol also makes it difficult for your body to regulate its temperature and interferes with hormone production.

Effects of alcohol withdrawal

A hangover is a milder form of alcohol withdrawal. Both have similar effects and symptoms. Drinking helps you feel calm, relaxed and even happy. Your nervous system adjusts to these effects. But when the alcohol wears off, your nervous system has to readjust. You may end up feeling more restless, anxious and irritable than before you drank.

Effects of alcohol metabolites

When the body processes alcohol, one of the byproducts is acetaldehyde. This substance can cause a fast pulse, sweating and nausea. In most people, the body breaks down acetaldehyde before it causes problems. But it can cause inflammation in organs, leading to uncomfortable symptoms.

If you have alcohol intolerance, you may have a genetic inability to process the acetaldehyde fast enough. You may feel the effects after drinking even a small amount of alcohol.

Effects of factors other than alcohol

  • Congeners: These compounds contribute to how alcohol tastes, smells and looks. Researchers think they also contribute to the intoxicating effects of alcohol and a hangover’s severity.
  • Using other drugs: Cigarettes, marijuana, cocaine and other drugs also produce intoxicating effects. Using them while consuming alcohol can affect hangover severity.
  • Personal differences: Researchers have found that feeling neurotic, angry, defensive or guilty over drinking can increase the hangover risk. If you have a family history of alcohol use disorder or are at high risk of developing it, you may also get more hangovers.

What are symptoms of a hangover?

Symptoms of a hangover include:

  • Depression, anxiety or irritability.
  • Disturbed sleep.
  • Dizziness and vertigo (a sensation of moving when you’re not).
  • Fatigue and weakness.
  • Headache, red eyes and sensitivity to light and sound.
  • Increased pulse and blood pressure; rapid heartbeat.
  • Muscle aches and weakness.
  • Nausea, vomiting and stomach pain.
  • Sweating and thirst.
  • Tremor (shaking).

You’re also more likely to have memory, concentration and coordination problems when you have a hangover. In general, the severity of your symptoms depends on how much you drank and for how long. But your health and other factors also play a role. Some people get a hangover after even one drink. Other people who drink heavily don’t get symptoms.

How long does a hangover last?

Typically, your symptoms are the worst when your blood alcohol level returns to zero. Symptoms can last about a day or possibly longer.

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