Walker's flight home from Mexico to Colorado, where he is now a co-owner of the Island Grill in Fort Collins, left at 8 a.m., and it was all he could do to get to the airport.

''If you can find a remedy for hangovers, that would be great,'' he said, voicing a sentiment familiar to anyone who has imbibed just a little too much and was sorry about it the next day.

In fact, recent studies suggest that help for at least some aftereffects of intoxication may not be too much to ask for.

Last summer, a group of doctors reported in The Archives of Internal Medicine that an extract from the fruit of the prickly pear cactus, taken in capsule form, was effective in staving off hangover symptoms like dry mouth and nausea.

Perfect Equation of Vista, Calif., financed the research and has patented the extract, which it says is derived from the skin of the prickly pear, Opuntia ficus.

Another company, Living Essentials of Walled Lake, Mich., markets Chaser, a pill containing activated calcium carbonate and activated charcoal. The company has financed a study of the dietary supplement, completed in 2002, its marketing director, Carl Sperber, said. The findings have not been published.

Experts say that despite such products, a true hangover cure remains elusive. And the hangover itself is imperfectly understood, perhaps because scientists have largely devoted their efforts to understanding alcohol dependence and the health effects of drinking.

Linda C. Degutis, an associate professor of emergency medicine and public health at Yale, said hangovers are ''incredibly understudied.''

Most popular remedies, including those sold over the counter, have no peer-reviewed research to back up their assertions. Some experts argue that even conducting such research raises ethical issues.

The development of a foolproof hangover cure, for example, might encourage people to drink more, knowing they could take a pill to avoid suffering the next day.

And the prospect of bus drivers' or airplane pilots' popping hangover pills and going to work is enough to give anyone pause.

Some researchers argue that hangovers impose such large costs on society that they have to be studied. No one has precise figures, but one study cited in the prickly pear article estimated the cost of alcohol-related problems, including hangovers, at nearly $150 billion a year in the United States.

Such studies ''are absolutely the next step,'' said Michael G. Shlipak, associate professor of medicine at the University of California, San Francisco, and an author of the prickly pear report.

One obstacle, however, may be that there is no consensus among scientists on how to define a hangover, Degutis said.

Achy and thirsty: Headache, thirst, nausea and muscle aches are probably the most familiar symptoms. Shlipak's study identified additional symptoms, including soreness, tremulousness and dizziness.

The effects of alcohol on the body are well known. When people drink, alcohol is quickly absorbed through the stomach lining. Most of it directly enters the bloodstream.

In the body, alcohol dilates blood vessels, creating a warm flush. It also depresses the central nervous system, resulting first in euphoria and then, as the alcohol wears off, anxiety, insomnia and depression.

Carried in the blood to the liver, alcohol breaks down into acetaldehyde and other byproducts that leave the body through the urine and the lungs.

Each body differs: On average, the body can process about one drink an hour, and sticking to that pace for a limited period should reduce the likelihood of a hangover, Degutis said. One drink is defined as one 12-ounce can of beer, 1.5 ounces of 80 proof whiskey or 5 ounces of wine.

But every person's body is different, she cautioned.

What happens when a drinker consumes enough alcohol to result in a hangover is a little less clear.

Shlipak and his colleagues have focused on the possibility that the immune system may react to toxic byproducts of fermentation in alcoholic beverages called congeners.

Congeners ''are poisons, and the body recognizes them as such,'' said Jeffrey G. Wiese, an associate professor of medicine at Tulane and also an author of the prickly pear study. As a general rule, Wiese said, the darker the alcoholic beverage is, the more congeners it has.

So according to studies, vodka generally causes less severe hangovers than, say, bourbon.

The researchers theorize that congeners may set off the release of cytokines, molecules that white blood cells release in fighting off viruses or other invaders. Cytokines signal inflammation in the body and cause the achy, tired feelings that people get when they have the flu.

Prickly pear extract, Shlipak and his colleagues suggest, helps by reducing the immune response to congeners. In their study, the researchers found that when graduate student testers drank five hours after taking the pill, they experienced less severe hangovers.

Living Essentials says Chaser works by capturing certain congener molecules, preventing the body from absorbing them.

''The secret is the activation of the calcium carbonate,'' said Sperber, the marketing director. ''You can't just take Tums and burnt toast and get the same effect.''

Shlipak said that he had not seen any studies on the effectiveness of Chaser but that charcoal, which does not bind to alcohol, could in theory block the absorption of the congeners in alcoholic beverages. That would mean that people who had consumed charcoal before drinking would still absorb all the alcohol, but might experience less severe hangover symptoms.

''It's possible,'' Shlipak said. ''Without commenting on how their product works or if it works, I think the concept is intriguing.''

Other researchers pointed out that anyone who could remember to pop any type of hangover pill through a night of drinking should be able to remember to drink water or even take the radical step of drinking a little less.

Drink more water: Dehydration also plays an important role in hangovers. The body tends to lose water as more alcohol is consumed, because alcohol is a diuretic, causing people to urinate more often regardless of how much water they are drinking.

That is why interspersing water or some other beverage with alcoholic drinks is a good idea, said Erik DeLue, a doctor of internal medicine at St. Margaret Mercy Hospital in Hammond, Ind., outside Chicago. Not only does the water rehydrate the body, DeLue said, but it also reduces the desire to consume more alcohol to slake thirst.

Several people interviewed about their hangovers said they had stumbled across possible cures by chance - from vitamin C to big, greasy breakfasts.

Doctors say there is little evidence to support most popular hangover remedies.

One thing that no one advises is more alcohol. While drinking to help a hangover may alleviate the problem of alcohol withdrawal, it can also impair mental functioning, and contribute to alcohol addiction and a worse hangover down the road, Degutis said.