The drug, called furosemide, is often given to racehorses with a history of bleeding in the respiratory tract -- or exercise-induced pulmonary hemorrhaging (EIPH).

In the 1980s, controversy arose surrounding the use of furosemide as a preventive measure for EIPH. Researchers aren't sure if furosemide has an effect on EIPH, but for nearly 30 years, thoroughbred trainers and owners have used furosemide to treat the disorder.

"We've found excellent evidence that associates furosemide with better performance," said Kenneth Hinchcliff, an associate professor of veterinary medicine at Ohio State.

Hinchcliff and his colleagues stopped short, however, of saying that the drug definitively improves performance. Also, the researchers aren't sure if furosemide has an effect on EIPH.

The research appears in the current issue of the Journal of the American Veterinary Medical Association. Hinchcliff co- authored the paper with Diane Gross, a graduate teaching assistant in the department of veterinary preventive medicine at Ohio State; Tom Wittum, an assistant professor of epidemiology at Ohio State; and Paul Morley, an assistant professor of epidemiology and biosecurity at Colorado State University.

After analyzing the race records of 22,589 thoroughbreds, the researchers found that 74 percent (16,761) of the horses were given furosemide prior to a race. These horses raced faster, were 1.4 times more likely to win a race, 1.2 times more likely to finish in the top three and earned an average of $416.00 more than the horses not receiving the drug.

While 85 percent of the horses in the study had received furosemide at some point in their lives, about 74 percent of thoroughbreds are likely to be running on the drug during a race, Gross said.

Furosemide -- sold under the trade name Lasix -- is "frequently used by humans for its diuretic effects," Morley said. Such drugs flush water from a person, thereby reducing body weight.

This diuretic effect may cause enhanced racing performance -- other studies found that horses on furosemide lost about 20 pounds of their pre-race body weight through urination. And if weight can affect performance, a horse that's lost 20 pounds would theoretically have a racing advantage. Race horses typically weigh about 1,000 pounds.

Furosemide is one of the only drugs allowed in all racing jurisdictions in the United States and Canada.

"The drug was essentially 'grandfathered' in North America," Hinchcliff said. "In most other racing jurisdictions in the world, the drug is not allowed."

The researchers don't know why furosemide seems to have a positive impact on a horse's speed and performance.

"Until now, the positive effect of furosemide on performance was generally assumed -- it hadn't been clearly demonstrated," Hinchcliff said.

Note: If no author is given, the source is cited instead.

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