Hangover: The Science Behind the Dreaded H Word

Hangover: The Science Behind the Dreaded H Word
Hangover: The Science Behind the Dreaded H Word.

No matter what medical problem I am explaining to my patients, their understanding of it helps in the treatment, and hangovers are no exception! With the holidays here, parties and get-togethers are sure to have an abundance of wine, eggnog, and other holiday cocktail concoctions. For some, this may lead to the dreaded hangover

Hangover—just the word is enough to make you feel queasy. If you’ve ever had one, you know the awful splitting headache, sandpaper mouth, roller coaster stomach, and constant visits to the bathroom.

Have you ever wondered how something so good could turn so wrong? In order to understand this, you have to understand some of the physiological processes the body goes through when alcoholic drinks are ingested.

Why You Get Hangovers

A hangover is defined by a combination of several unpleasant physical impairments after a time of heavy drinking. The physical symptoms of a hangover include fatigue, headache, muscle aches, and dehydration, as well as less apparent effects of increased blood pressure and heart rate. All of these side effects can be attributed to one simple component of an alcoholic beverage. 

As you drink your beer, wine or liquor, you ingest a molecule called ethanol, otherwise known as ethyl alcohol, or simply alcohol.  As ethanol makes its way to the liver to be metabolized, 10-20% of the ethanol is taken into the bloodstream by the stomach. The ethanol then circulates around the body, causing all sorts of effects, including one of the most prevalent hangover symptoms: dehydration.

Drinking an alcoholic beverage causes an increased frequency of urination. This happens because alcohol is a diuretic, and makes the body expel water. As alcohol makes contact with the pituitary gland in the brain, it blocks the expression of antidiuretic hormone (ADH), and your kidneys start to send water straight to the bladder, instead of reabsorbing it.

This dehydration makes the body send a signal to find water, which is why you experience a dry mouth.

Alcohol also causes vomiting, sweating, and diarrhea through other mechanisms, which also leads to dehydration. Ethanol itself irritates the lining of the intestines and stomach, causing inflammation. Ethanol can also cause delayed stomach emptying, and increases the production of intestinal and pancreatic secretions, causing vomiting nausea, and general discomfort. Alcohol also has the potential to cause more long-lasting changes in your gut by disrupting the microbiome and causing increased intestinal permeability.

Low blood sugar, known as hypoglycemia, can be caused by ethanol as well, which is what makes you feel tired. As ethanol is metabolized in the liver, it becomes acetaldehyde, which is further converted to a nontoxic molecule known as acetic acid, the molecule that makes up vinegar. The acetic acid is later broken down in a process known as the citric-acid cycle, creating lactic acid.

Lactic acid lowers the pH of its environment and causes soreness; the same soreness from extraneous workouts. The production of lactic acid into body fluids, known as lactic acidosis, inhibits glucose production, and with enough drinking will exhaust stored glucose in the liver. Glucose is the primary source of energy for the body and brain, and the lack of it will contribute to the hangover symptoms of fatigue, weakness, and headaches.

The metabolism of ethanol to acetaldehyde is done by an enzyme called alcohol dehydrogenase (because it removes hydrogen from ethanol). Men actually have a higher concentration of alcohol dehydrogenase and that is why women are advised not to go “drink-for-drink” with their male counterparts. Acetaldehyde itself is a highly reactive toxic molecule. Acetaldehyde binds to proteins and other compounds causing all sorts of problems in the body. Although acetaldehyde is broken down very quickly into acetic acid, it can still cause hangover symptoms.

Although alcohol itself seems to be the cause of all hangover symptoms, there is another component of alcoholic beverages that may induce hangovers as well. They are a group of compounds known as congeners. They are a by-product of the fermentation and processes used to create beer, wines and liquors. Congeners contribute to the taste, smell and appearance of beverages, but may also contribute to hangovers. Research has shown that drinks composed of higher amounts of pure ethanol produce fewer hangover effects than their congener containing counterparts such as whiskey, brandy, and red wine.

There you have it, the science behind the dreaded hangover! Now after understanding the physiological process by which a hangover occurs, you may be wondering what is the best way in which to combat it. Obviously, the best way is to drink minimally, or not at all. However, if you feel you simply cannot live without that holiday cheer and choose to drink, drink clear drinks as they contain fewer congeners. Additionally, stay hydrated, obtain electrolytes, and make sure to stay nourished throughout your night of drinking.


Klaus Roth, 'Chemistry of a Hangover — Alcohol and its Consequences Part 1-3', Chemie in unserer Zeit/Wiley-VCH, DOI: 10.1002/chemv.201000089 

Montastruc, P. L’alcool exagere la soif. (Alcohol exaggerates thirst). HCEIA Informations 4:41–42, 1986.

Chapman, L.F. Experimental induction of hangover. Quarterly Journal of Studies on Alcohol 5(Suppl. 5):67–86, 1970.

Vishnudutt, P. Alcohol, Intestinal Bacterial Growth, Intestinal Permeability. Alcohol 2008 42(5).

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