https://www.nytimes.com/2019/09/11/sports/horse-racing/justify-drug-test-triple-crown-kentucky-derby.html
Only a handful of racing officials and people connected to Justify knew about the failed drug test, which occurred April 7, 2018, after Justify won the Santa Anita Derby. He tested positive for the drug scopolamine, a banned substance that veterinarians say can enhance performance, especially in the amount that was found in the horse.
Justify was undefeated at the time, but he still needed to finish first or second in the Santa Anita Derby to qualify for the Kentucky Derby, on May 5. While the colt won at Santa Anita, the failed drug test would mean disqualification and forfeiture of both the prize money and the entry into the Kentucky Derby that came with the victory.