Clenbuterol Banned in Quarter Horse Racing

Clenbuterol (trade name Ventipulmin®) is a bronchodilator that is helpful for horses with heaves, an inflammatory condition that causes the airways to constrict. Horses with heaves have a hard time exhaling and are often intolerant of exercise.

Figuring that more air would be a benefit to racehorses, trainers have sometimes given clenbuterol to horses that did not have heaves. Use of this drug has not been shown to have a beneficial effect on breathing in healthy horses. Some side effects such as increased muscle mass, however, are believed to have a performance-enhancing role.

Clenbuterol has been regulated at some Thoroughbred tracks, and has now been completely eliminated in Quarter Horse racing (in the US). The American Quarter Horse Association Racing Council put the ban in place to stop misuse of the drug after routine testing turned up a large number of Quarter Horses in race training with positive test results for clenbuterol.

Race trainers might have been inadvertently handicapping their horses by long-term use of clenbuterol. Trials conducted at the University of Pennsylvania’s New Bolton Center showed that giving horses clenbuterol initially opened the airway, but after about 14 days this effect was diminishing. When administration was continued for 21 days, airway function actually dropped below the initial level.

In horses with heaves, steroid administration maintains clenbuterol’s efficacy. Treatment of heaves involves environmental change along with several drugs, depending on the severity.