No tests in people.

Take two Rebound pills with every two alcoholic drinks, "enjoy the party, and wake up in the morning clear-headed and able to function," promises the Dynamarketing Group of San Diego, California. "You'll wonder why you ever drank without it."

Rebound is "a new, safe natural dietary supplement, clinically proven to help prevent hang-overs before they start ..." says the company's Web site. The concoction (barley grass juice powder, citric and other acids naturally found in the body, amino acids, and vitamins) supposedly works by suppressing the formation--and speeding the removal--of acetaldehyde, the most toxic byproduct of alcohol metabolism.

"Everyone who tries it is stunned to discover that it actually works," marvels Patrick Cochrane, CEO of Dynamarketing and author of The Kitchen Table Millionaire, a guide to spotting an opportunity, starting a business, and making a fortune.

"But acetaldehyde is only one factor contributing to hangovers," says Dena Davidson, a professor of psychiatry and an alcohol researcher at the Indiana University School of Medicine in Indianapolis. "There are many others, such as dehydration and impurities in the alcohol."

Targeting just acetaldehyde, says Davidson, "wouldn't necessarily have a noticeable impact."

Where does Dynamarketing's "clinical proof" come from? In one study, adding barley grass to beer slowed the conversion of alcohol into acetaldehyde after three months. (1) In another, combinations of some of Rebound's components suppressed acetaldehyde levels in mice that had been injected with alcohol. (2) (It wasn't clear whether the rodents woke up hangover-free, though.)

Neither Rebound nor its components has ever been tested on hangovers in humans. But "clinically proven in mice" (even if it were true) won't make you a millionaire.

(1) J. Agric. Food Chem. 46:1529, 1998.

(2) Res. Commun. Chem. Pathol. Pharmacol. 13: 125, 1976.