The Kentucky Horse Racing Commission said Wednesday that retrospective testing of blood samples taken from horses that ran in the 2012 Kentucky Derby and Kentucky Oaks were negative for dermorphin. The testing was done by HFL Sports Science Laboratory in Lexington.
The commission did not say how many horses were tested.
A recent outbreak of positive tests for the banned substance in several states prompted the retesting.
Dermorphin is sometimes referred to as "frog juice" because the potent painkiller is found naturally in secretions of a South American tree frog.