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What is a hangover and why do we get one?

A hangover is the experience of various unpleasant physiological effects following heavy consumption of alcoholic beverages. The most commonly reported characteristics of a hangover include headache, nausea, sensitivity to light and noise, lethargy,dysphoria, diarrhoea and thirst, typically after the intoxicating effect of the alcohol begins to wear off. While a hangover can be experienced at any time, generally speaking a hangover is experienced the morning after a night of heavy drinking. In addition to the physical symptoms, a hangover may also induce psychological symptoms including heightened feelings of depression and anxiety.

Hypoglycaemia, dehydration, acetaldehyde intoxication, and glutamine rebound are all theorized causes of hangover symptoms. Hangover symptoms may persist for several days after alcohol was last consumed. Approximately 25-30% of drinkers may be resistant to hangover symptoms. Some aspects of a hangover are viewed as symptoms of acute ethanol withdrawal, similar to the longer-duration effects of withdrawal from alcoholism, as determined by studying the increases in brain reward thresholds in rats (the amount of current required to receive from two electrodes implanted in the lateral hypothalamus) following ethanol injection. Dehydration is caused by alcohol's ability to inhibit the effect of anti-diuretic hormone on kidney tubules, which leads to a hyperosmolar state, which in turn causes shrinking of (by loss of water) the brain cells which causes hangover.

Symptoms...

An alcohol hangover is associated with a variety of symptoms that may include dehydration, fatigue, headache, body aches, vomiting, diarrhoea, flatulence, weakness, elevated body temperature and heart rate, hypersalivation, difficulty concentrating, sweating, anxiety, dysphoria, irritability, sensitivity to light and noise, erratic motor functions (including tremor), trouble sleeping, severe hunger, halitosis, and lack of depth perception. Many people will also be repulsed by the thought, taste or smell of alcohol during a hangover. The symptoms vary significantly from person to person, and it is not clear whether hangovers directly affect cognitive abilities.

Causes...

Ethanol has a dehydrating effect by causing increased urine production (diuresis), which causes headaches, dry mouth, and lethargy. Dehydration also causes fluids in the brain to be less plentiful. This can be mitigated by drinking water before, during and after consumption of alcohol. Alcohol's effect on the stomach lining can account for nausea.

Alcohol consumption can result in depletion of the liver's supply of glutathione and other reductive detoxification agents, reducing its ability to effectively remove acetaldehyde and other toxins from the bloodstream. Additionally, alcohol induces the CYP2E1 enzyme, which itself can produce additional toxins and free radicals.

A 2009 study provided evidence that darker-coloured liquors, such as bourbon, cause worse hangovers than lighter-coloured liquors, such as vodka. The higher amount of congeners found in darker liquors compared to lighter ones was indicated as the cause.

In a 2006 study, an average of 14 standard drinks (330 ml bottles) of beer was needed to produce a hangover, compared with only 7 to 8 drinks of wine or liquor. 

It is often said that hangovers grow worse as one ages; this is thought to be caused by declining supplies of alcohol dehydrogenase, the enzyme involved in metabolising alcohol.

It is a common thought that mixing drinks leads to a worse hangover. Empirical evidence tends to suggest otherwise.

Cures...

Hangovers are poorly understood from a medical point of view. Health care professionals prefer to study alcohol abuse from a standpoint of treatment and prevention, and there is a view that the hangover provides a useful, natural and intrinsic disincentive to excessive drinking.

Within the limited amount of serious study on the subject, there is debate about whether a hangover might be prevented or at least mitigated; additionally, there is a vast body of folk medicine and simple quackery. There is currently no empirically proven mechanism for prevention except reducing the amount of ethanol consumed, or for making oneself sober other than waiting for the body to metabolize ingested alcohol, which occurs via oxidation through the liver before alcohol leaves the body. A four-page literature review in the British Medical Journal concludes: "No compelling evidence exists to suggest that any conventional or complementary intervention is effective for preventing or treating alcohol hangover. The most effective way to avoid the symptoms of alcohol induced hangover is to avoid drinking."

• Rehydration
• Vitamin B₆ (pyritinol)
• Hair of the dog... although I have previously found out that this simply delays the hangover rather than cures it!
• Yeast-based extracts
• Food and water
• Oxygen