Levamisole Metabolizes To Appear As A Performance Enhancer, Is It? What Does It Do?

June 25, 2020

By: Leila Elliott

It was in early February that news of horse trainer Joe Sharp having eight of his winning equine charges disqualified to last in each of their races at Fair Grounds race track. Each was due to the positive test results for banned substances, the substance in question being Levamisole—a drug that can be found in some deworming medications.

What is Levamisole, and what makes it a performance enhancing drug?

Used to eliminate nematodes in livestock (pigs, cattle, sheep), Levamisole can be found in a variety of deworming medications such as Prohibit. . Additionally, it has been used in horses off label as an immunostimulant and as a medication in the treatment of EPM (Equine Protozoal Myelitis).

In horses, Levamisole metabolizes to aminorex and possibly pemoline which are considered potent stimulants assigned a 1/A Classification in the Association of Racing Commissioners International Uniform Classification of Foreign Substances

While Levamisole can be used in the horse, its resulting positive Aminorex test creates a difficult scenario for users, as its presence creates the look of an intentional Aminorex dosage even if used as a dewormer. It is because of this that Levamisole has itself become a Class (2) medication, while Aminorex is a Class (1), meaning “stimulant and depressant drugs that have the highest potential to affect performance and that have no generally accepted medical use in the racing horse,” according to the ARCI.

Three more of Sharp’s horses tested positive for Levamisole after wins at Churchill Downs in early March, bringing the trainer’s total number of disqualifications to eleven due to the use of the same prohibited medication, Levamisole. According to Daily Racing Form, Sharp reported that the three additional positive tests all correlated with the initial administration of Prohibit dewormer, which Sharp began using in his barn in November of 2019. He discontinued his use of the medication after repeated positive tests on a number of his horses in the following month. 

“There are no more surprises, at least none to my knowledge…,” said Sharp, following the most recent three disqualifications. The three horses in question all raced at Churchill Downs from November 23 through November 30, the same time frame that the Levamisole-containing Prohibit dewormer was being used in Sharp’s barn. 

Commenting to BloodHorse following the eight initial disqualifications, Sharp told reporters “As soon as we found out, we took it out of the barn on December 12. A lot of these horses had been through the test barn, and then you stop use, and I then find out that stuff stays in their system.”

Sharp was fined $1,000 for each of the first eight horses to test positive at Fair Grounds, pending a steward’s hearing result for the following three positives at Churchill Downs.

Nice score King! @jonathanstettin Well played with the 4 singled on one ticket. 2 times! Big congrats.

Michael R. Snow (@theWynnDough) View testimonials