The new tests have discovered the illegal substance, dermorphin, in more than 30 horses from four U.S. states in recent days, The New York Times reported Tuesday.
No trainers have yet been charged, but regulators told the newspaper it's only a matter of time.
"We hear about some pretty exotic stuff. Frog juice -- this is exotic," Dr. Steven Barker, who directs the testing laboratory at Louisiana State University, told the Times about the drug, which is 40 times more potent than morphine.
Barker said most of the dermorphin being used likely has been artificially synthesized.
"There's a lot out there, and that would be an awful lot of frogs that would have to be squeezed. There are a lot of unemployed chemists out there," he said.
"For a racehorse, it would be beneficial. The animal wouldn't feel pain, and it would have feelings of excitation and euphoria," said Craig W. Stevens, a professor of pharmacology at Oklahoma State University who has studied dermorphin, adding the drug makes animals "hyper."
"This is a tough issue," said Edward J. Martin, president of Racing Commissioners International. "It's a cat-and-mouse game. As soon as you call out dermorphin, they will try something else. That is the daily battle that goes on."