Why Alcohol Causes a Hangover

Anyone who's consumed too much alcohol knows the misery of the morning after. As to what actually causes a hangover, a variety of factors contribute. Most importantly, these include direct effects of alcohol on the body, such as dehydration. Other symptoms can result from alcohol withdrawal, certain chemicals your body produces when you drink alcohol, behaviors associated with drinking, and your personal characteristics.

Hangover Effects Caused by Alcohol

Alcohol directly contributes to hangover symptoms in several ways:

• Dehydration and electrolyte imbalance: The increased urine production, sweating, vomiting, and diarrhea that alcohol consumption causes dehydrates the body. This causes many common hangover symptoms such as thirst, weakness, dry mouth and nose, dizziness, and lightheadedness.
• Gastrointestinal disturbances: Excessive alcohol consumption can irritate the stomach and intestines, causing inflammation of the stomach lining (gastritis), delayed stomach emptying. Chemicals secreted by the pancreas and intestines can cause abdominal pain, nausea, and vomiting.
• Low blood sugar: Alcohol consumption can inhibit glucose production and deplete glucose reserves stored in the liver. Because glucose is the brain's main energy source, low blood sugar contributes to the fatigue, weakness, and mood disturbances of hangovers.
• Disruption of sleep and other biological rhythms: Alcohol-induced sleep is usually of shorter duration and poorer quality than normal sleep, causing fatigue. Alcohol also can disrupt the body's daily temperature rhythm, nighttime secretion of growth hormones, and cortisol release, all of which can produce symptoms akin to jet lag.
• Headache: Alcohol intoxication causes widening of blood vessels (vasodilation), which can cause a headache. Alcohol consumption also affects the production of histamine, serotonin, and prostaglandins—hormones thought to contribute to headaches.
• Alcohol withdrawal: Heavy drinking depresses the central nervous system. When alcohol is withdrawn, it can go into an unbalanced hyperactivity state.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: In your body, alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) break alcohol molecules down so they can be eliminated. Alcohol is metabolized by ADH to acetaldehyde, which is then broken down further into acetate. Some people have genetic variants of ALDH that allow acetaldehyde to accumulate and cause toxic effects. Although acetaldehyde is no longer in the body when the blood alcohol level reaches zero, its toxic effects can persist into the hangover period, researchers believe.

Hangover Effects Caused by Other Factors

Factors other than alcohol can contribute to a hangover, too. These include:

• Congeners: Most alcoholic beverages contain congeners, chemicals that contribute to their taste, smell, and appearance. These compounds can exacerbate hangover symptoms. Clear liquors such as gin and vodka cause fewer hangover effects than whiskey, brandy, and red wine because they contain fewer congeners.
• Use of other drugs: People who drink heavily often use other drugs, and many smoke cigarettes. These substances can cause their own set of hangover-like symptoms. Although the use of marijuana, cocaine, and other drugs can contribute to situations that foster excessive alcohol intake, their exact effects on alcohol hangovers are not known.
• Personal influences: Certain personality traits, such as shyness, intensify hangover feelings and create a sense of "hangxiety." Negative life events, feelings of guilt, and the risk of alcoholism often produce acute hangover symptoms.
• Family history: People who have a family history of alcoholism tend to have worse hangovers than drinkers who have no family history of alcoholism. However, keep in mind that people with a family history of alcoholism generally consume more alcohol than those who do not have a family history.

When to See a Doctor

In and of themselves, hangovers are not life-threatening and will subside without medical intervention. However, if you have frequent hangovers that interfere with daily life, consider seeing a doctor to evaluate whether you might have alcoholism. Help and effective treatment are available.

The Bottom Line

Hangover symptoms are the result of several factors, two of which are dehydration and the toxic effects of alcohol on the body. You can counter dehydration quickly with water or sports drinks that replace electrolytes; however, only time can reverse the toxic effects of alcohol on your central nervous and gastrointestinal systems.