Give a drunk some coffee and what do you get ? A drunk full of coffee of course. No, just kidding. Actually although coffee won't sober you up, it's known to constrict blood vessels in the extremeties, while alcohol dilates the blood vessels. Dilated blood vessels in the head can cause migranes. So it may help counteract a headache somewhat. On the other hand, due to coffee's diuretic action, it may make your tummy and general mood worse. To reduce dehydration, it's best to drink a glass of clear water for every glass of alcohol. Basically a hangover is due to a builup of the breakdown products of alcohol, such as acetaldehyde and compounds which give it its taste, color and smell known as congeners. These substances are toxic to the human body, but fortunately we have enzymes that will get rid of them. These are the substances thought to cause the effects of a hangover.
Really, only patience and time will get rid of the nasty side effects.
Hope that helps,
Peter Bosani.
P.S. For more info on food and its lore check out: www.myspace.com/bosani