Though it stands by its equine drug-testing program, the Ontario Racing Commission said March 13 it will allow trainers with positives for aminorex, a methamphetamine-like substance, to enter horses in races in the province. The investigation into the drug’s origin will continue.

At least 10 trainers of Standardbreds in Ontario have had positives called for aminorex, a Class 1 drug with the ability to affect performance. The drug, which officials said hasn’t been commercially produced since the 1980s and is similar to methamphenamines called “Ice” and “Euphoria,” isn’t hard to manufacture, said Scot Waterman, DVM, executive director of the Racing Medication and Testing Consortium.

Canadian officials in a release said the “unprecedented number” of positives has led them to confirm the reliability of drug tests and clarify the eligibility status of affected trainers.

“The evidence to date and the pattern of events suggest we have a unique situation,” racing commission executive director John Blakney said in a statement. “We need time to get to the root cause and are concentrating our investigative efforts to determine the source of the aminorex, how it was administered, and the person or persons responsible for its distribution. As there is no therapeutic benefit to this drug, it is imperative that more be learned about such things as how long it will take for the Aminorex to dissipate from the systems of the horses that have tested positive