Why do hangovers occur?

          Sant P. Singh, a professor and chief of endocrinology, diabetes and metabolism at Chicago Medical School, offers this answer:

          Several factors appear to be involved in getting a hangover—the unpleasant consequence visited on 75 percent ofthose who drink alcohol to intoxication. The effects includeheadache, nausea, vomiting, thirst, dryness of the mouth,tremors, dizziness, fatigue and muscle cramps. Often there is an accompanying slump in cognitive and visual-spatial skills.

          A hangover has been suggested to be an early stage of alcohol withdrawal. Mild shakiness and sweats can occur; some people may even hallucinate. Acetaldehyde, a toxic breakdown product of alcohol metabolism, plays a role in producing symptoms. Chemicals known as congeners that are formed during alcohol processing and maturation also increase the likelihood and severity of a hangover; as a rule of thumb, the darker the liquor, the more congeners it contains. The toxins in congeners are distributed throughout the body as the liver breaks down the alcohol. Last, hangovers cause changes in the blood levels of various hormones, which are responsible for some symptoms. For example, alcohol inhibits antidiuretic hormone, which leads to excessive urination and dehydration. Blood aldosterone and renin levels also increase with a hangover—but unlike antidiuretic hormone, they do not correlate well with symptomatic severity, so their role is less clear.
            
            Individuals are more prone to develop a hangover if they drink alcohol rapidly, mix different types of drinks, and do not dilute the absorption of liquor by eating food or drinking nonalcoholic beverages. Sugar and fluids can help overcome the ensuing hypoglycemia and dehydration, and antacids can reduce nausea. To reduce headache, anti-inflammatory drugs should be used cautiously: aspirin may irritate the stomach, and the toxic effects of acetaminophen on the liver can be amplified by alcohol. Other drugs have been used to treat hangovers, but most have questionable value.