Researchers investigate effects of furosemide on racehorses


Washington State University researchers received over $370,000 for a 2-year study



Researchers at Washington State University have received over $370,000 for a 2-year study looking into the impact of a drug administered to thoroughbred racehorses. Furosemide, commonly known as Lasix, is given to horses before most races across the United States to reduce bleeding in their lungs.

Furosemide is a diuretic that has shown to reduce the prevalence and severity of exercise-induced pulmonary hemorrhage (EIPH), which can cause bleeding in the lungs during exercise. The drug has spiked controversy from those doubting its effectiveness, believing it leads to other health ramifications, and creating a public perception issue for horseracing. The use of furosemide is currently prohibited on race days abroad, and a permanent ban within the United States is under consideration.1

“We hypothesize that our study will show horses that regularly get furosemide before racing have more races and longer careers than those that don’t,” Warwick Bayly, BVSc (Honors), PhD, MS, leading the research alongside Macarena Sanz, DVM, PhD, MS, said in an organizational release.1 “The results of this study are going to help guide the final decision on the future use of furosemide.”

The grant was awarded to WSU by the Horseracing Integrity and Safety Authority (HISA), which was founded in 2020 by Congress to regulate thoroughbred racing in the US. Although most tracks have applied for and received waivers while studies are being performed on the drug, HISA essentially banned its use.1 Despite having waivers, major racetracks, such as the Kentucky Derby, have banned the same-day use of furosemide in horses under the age of 3 years.

According to the release, researchers at WSU plan to analyze information gathered from around 30,000 racehorses. The work will start by breaking down the career trajectories of horses that started competing in 2011 and follow their performances until 2019. The goal of this phase is to give researchers a better understanding of how regular furosemide treatment correlates with increased career longevity and race participation.

Researchers also plan to investigate the impact of banning furosemide on horses' careers and the number of starts for horses 2 years old. The plan is to have researchers compare horses that raced in 2011-2019, before the ban, and horses racing post-ban, from 2021-2025. Data will be collected from videos of horses at racetracks in early 2024 to evaluate EIPH’s severity and influence on participation over 18 months.1 The results of each study should provide crucial information to help HISA make informed future regulations on the use of furosemide in thoroughbreds before racing.

“There are many things that result in a horse ending its career, and there are a lot of things that determine how many races it would have,” explained Bayly.1 “Our theory is that one of those determinants is the severity of the EIPH. A couple of really clever statisticians are participating in the study, and we have to sift through all this data and try and work out whether or not the frequency of Lasix administration is related to career duration.”

In 2015,2 the American College of Veterinary Internal Medicine (ACVIM) published a consensus statement in the Journal of Veterinary Internal Medicine, on the use of the effects of furosemide on the athletic capacity of horses and its efficacy of prophylactic interventions for EIPH.2 ACVIM put together a panel of experts to assess evidence in peer-reviewed literature and found much of the evidence out there was low to very low quality with studies frequently lacking adequate statistical power, and stated that furosemide is efficacious in decreasing the incidence as well as severity of EIPH. The conclusion of the ACVIM investigation strongly recommends EIPH be considered a disease, but a weak recommendation for using furosemide in managing this condition in racehorses.2

In 2026, HISA expects to make its final decision on furosemide based on the findings in studies it has funded, including this study at WSU.


  1. WSU to study effect of controversial drug on racehorses. News release. Washington State University. April 23,2024. Accessed April 24, 2024.
  2. Hinchcliff KW, Couetil LL, Knight PK, et al. Exercise Induced Pulmonary Hemorrhage in Horses: American College of Veterinary Internal Medicine Consensus Statement. J Vet Intern Med. 2015;29(3):743-758. doi:
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