Why Alcohol Causes a Hangover

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Hangovers are caused by a variety of factors including the direct effect of alcohol on the systems of the body as well as other factors associated with drinking behavior.

Although the direct effect of excessive alcohol consumption on the body produces the most unpleasantness, other symptoms can result from the withdrawal of alcohol from the body, the effects of metabolites produced when alcohol is consumed, other chemicals in alcoholic beverages, behaviors associated with drinking, and personal characteristics of the drinker.

Direct Alcohol Effects

There are several ways that alcohol directly contributes to hangover symptoms:

  • Dehydration and Electrolyte Imbalance: Because alcohol consumption increases urine production it causes the body to dehydrate leading to many common hangover symptoms including thirst, weakness, dryness of mucous membranes, dizziness, and lightheadedness. Because sweating, vomiting, and diarrhea also can occur as a result of excessive drinking, the body can lose additional fluids and electrolytes.
  • Gastrointestinal Disturbances: Excessive alcohol will irritate the stomach and intestines causing inflammation of the stomach lining and delayed stomach emptying. Alcohol can also produce fatty liver, gastric acid, and pancreatic and intestinal secretions, all of which can cause abdominal pain, nausea, and vomiting.
  • Low Blood Sugar: Alcohol consumption can inhibit glucose production in the body and deplete the reserves of glucose stored in the liver. Because glucose is the main energy source of the brain, low blood sugar can produce symptoms of fatigue, weakness and mood disturbances experienced during hangovers.
  • Disruption of Sleep and Other Biological Rhythms: Alcohol-induced sleep is usually of shorter duration and poorer quality than normal sleep. This can cause the fatigue experienced during a hangover. Alcohol also can disrupt the body's daily temperature rhythm, nighttime secretion of growth hormones, and the release of cortisol, all of which can produce "jet lag" type symptoms during a hangover.
  • Headache: Alcohol intoxication can result in the widening of blood vessels (vasodilatation), which can lead to a headache. Alcohol consumption also affects histamine, serotonin, and prostaglandins, hormones thought to contribute to headaches.
  • Alcohol Withdrawal: Heavy drinking depresses the central nervous system. When alcohol is withdrawn, the central nervous system can go into an unbalanced hyperactivity state or an "overdrive" state. This can cause the tremors and rapid heartbeat associated with hangovers. Many of the signs and symptoms of hangover overlap the symptoms of alcohol withdrawal syndrome.
  • Effects of Alcohol Metabolites: Alcohol is metabolized by an enzyme called acetaldehyde, then a second enzyme (aldehyde dehydrogenase [ALDH]) metabolizes acetaldehyde to acetate. Some people have genetic variants of ALDH that allow acetaldehyde to accumulate in the body and cause toxic effects. Although acetaldehyde is no longer in the body when the BAC level reaches zero, the toxic effects of it may persist into the hangover period, researchers believe.

Effects of Factors Other Than Alcohol

There are factors other than alcohol that can contribute to a hangover. Some of them include:

  • Congeners: Most alcoholic beverages contain chemical compounds, known as congeners, that contribute to the taste, smell and appearance of the beverage. These compounds can contribute to the symptoms of a hangover. Research has shown beverages that are basically pure alcohol, such as gin or vodka, cause fewer hangover effects. Beverages that contain more congeners such as whiskey, brandy, and red wine tend to cause more hangover symptoms.
  • Use of Other Drugs: People who drink heavily often use other drugs and many of them smoke cigarettes. These substances can cause their own set of hangover type symptoms. Although the use of marijuana, cocaine and other drugs can contribute to conditions leading to getting a hangover, their exact effects on alcohol hangovers are not known.
  • Personal Influences: There is some research that shows that people with certain personality traits have greater hangover symptoms. These include neuroticism, anger, and defensiveness. Negative life events and feelings of guilt also are associated with experiencing more hangovers. People who are at a higher risk of developing alcoholism also experience more acute hangover symptoms.
  • Family History: People who have a family history of alcoholism have a tendency for increased hangover symptoms compared with drinkers who have no family history of alcoholism. However, people with a family history of alcoholism generally consume more alcohol than those who do not have a family history.

The Bottom Line

Although many factors can contribute to hangover symptoms, the two main factors are dehydration and the poisoning (toxic) effects of alcohol on the body's systems. Dehydration can quickly be reversed, and its symptoms relieved, with water or sports drinks that replace electrolytes, but only time can reverse the toxic effects of alcohol on the central nervous system and the gastrointestinal systems.

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