How Does Lasix Enhance Performance in Horses?

By: Wes Bright, Staff Member

If you are reading this blog post, it is likely you are already aware of the controversy the horse racing industry faces over the use of Furosemide (better known as Lasix). Most agree Lasix does enhance performance in horses to some degree.[1] However, much of the problem lies in how it enhances performance.

Those in favor of Lasix as a race day medication have an opinion much like Thomas Tobin's, a professor at the University of Kentucky Gluck Equine Research Center.[2] Tobin was quick to point out that some studies do not factor in that "EIPH (Exercise Induced Pulmonary Hemorrhage) causes horses to run slower and Lasix acts to prevent and lessens EIPH."[3] Instead of enhancing a horse's performance, Lasix simply allows a horse to be healthy. Yes, it is likely a healthy horse will run faster than one with blood-filled lungs.

We allow athletes in other sports to take measures to assure that they are healthy enough to play, such as a basketball player draining the fluid from his knees.[4] Who is going to tell Dirk Nowitzki that he has to let his knee heal and if it doesn't, well, tough luck, your career is over? Yet, there have been proposals to do that very thing to horses.[5]

It is common knowledge that the lighter something is, the faster it will go. It stands to reason a horse that has lost 2% of its body weight due to Lasix will be faster than one that has not.[6] Many say this is the reason for the enhancement in performance and point to studies like the one done by the University of Pennsylvania.[7] They found bleeders as well as non-bleeders to be faster when Lasix is administered. Assuming this study is without fault, should it matter that horses are faster because they lose weight? I again turn to the treatment of other professional athletes. We allow jockeys in the same industry to cut weight, even though they sometimes go to extreme measures to do it.[8] Athletes involved in wrestling or boxing cut weight in order to fight in a lower class.[9] These measures have the same effects on humans as Lasix has on horses, yet I do not hear an uproar over it.

In other sports we ban performance enhancers due to their negative long-term effect on the body. The opposite is true for Lasix. It reduces the negative effects of EIPH. Many who oppose its use hear the word "Lasix" and "performance enhancer" and immediately think it must have negative effects, while the opposite is true.

If there wasn't an advantage gained by Lasix, using it would not be a normal occurrence.[10] What causes the advantage will remain up for debate. My answer: If it helps the horse and doesn't give an advantage, then who cares?
[1] FAQ About the Study and Project, University of Pretoria Equine Research Center, default.asp?ipkCategoryID=5218.
[2] Erica Larson, EIPH and Furosemide Use In Racehorses Explained, (Oct. 4, 2012),
[3] Id.
[4] Tim MacMahon, Dirk Nowitzki has knee drained againESPNDallas (Oct. 12, 2012), /nba/story/_/id/8495123/dirk-nowitzki-dallas-mavericks-knee-drained-second-time-month.
[5] Bruce Schreiner, Proposed race-day drug ban resurfaces in KentuckyYahoo Sports (May 16, 2012),
[6] See FAQ, supra note 1.
[7] Associated Press, Lasix Found to Aid Horses' (May 7, 1990), 1990-05-07/sports/sp-311_1_racing-performance.
[8] Matthew Percia, What Sports Use a Rapid Weight Loss Method? (Feb. 21, 2011),
[9] Id.
[10] Ed Springston, Governor Beshear Purposely Putting Horse Racing at Risk in KY? (Jun. 18, 2012),