The Lasix debate has reached its fever pitch, and I have avoided it thus far. Backed off by accusations that I am merely a scientist and not a race trainer, I have remained fairly quiet.

But. I am a horsemen. I am a scientist. And maybe those two things needs combined for an opinion.

An opinion based on fact. Not anecdote. Not legend. And more importantly, not propaganda.

Furosemide (Lasix) is a drug used to prevent or at least minimize outward bleeding of horses in strenuous work. This bleeding is called epistaxis, and mostly occurs when a horse suffers from grade 4 Exercise-Induced Pulmonary Hemorrhage (EIPH). There are three lower grades (1-3) which can be detected by endoscopy, but are not outwardly noted as a horse who bleeds.

While 55% of thoroughbred racehorses experience that grade 1-3 EIPH, it is known that a mere 4% of actually experience epistaxis or outwardly bleed (Preston et al (2015)).

And yet a staggering 93% of thoroughbred racehorses in North America race on Lasix.

4% bleed. 55% have the disease. 93% are treated.

This doesn’t add up.

Industry would lead us to believe that the banning of Lasix will lead to an outcry from PETA for animal welfare because SO MANY horses will be bleeding in public. And yet science disagrees, showing that very few actually will.

Not to mention, industry has filled our minds with this idea that Lasix saves horses. If we don’t use it, horses lungs will fill with blood and drop dead. They tell us that it is good animal welfare to give the horses these drugs and minimize their pain and suffering. Without the drug, we will be neglecting animals. With the drug, we will be helping them.

And all I can say is… What?

Veterinary medicine is a practice built on diagnosing and treating a disease, not individual symptoms.

And Lasix? Lasix is the treatment of a symptom, not a disease. Lasix masks the symptom of bleeding, but doesn’t treat the disease of EIPH. Not to mention, it doesn’t truly mask the symptom of bleeding all that well, and has been shown to decreases only 1 EIPH grade score in only 68% of horses (Sullivan et al. (2015) / Hinchcliff et al. (2009)).

So it works in 68% of the 55% of horses which suffer from the disease. Ok, then it’s benefiting 37.4% of racehorses.

Then why are 93% getting it?

Maybe more interesting is our other option in minimizing EIPH score.

Nasal strips (Geor et al (2001)/ Kindig et al. (1985)). Pretty damned effective and a whole lot safer.

One is a caustic diuretic and the other a strip applied to the skin to open airways. And yet the one we are grasping onto? The drug.

And what does treat the condition of EIPH? Not Lasix, not Flair strips, not withholding water or even administering vodka.

Rest. Simple rest.

In other countries, this is already implemented. A horse bleeds, and is withheld from training or racing from a range of 30-180 days. Bleeds a second time? Longer. And while these other racing locales implement a treatment for the disease, we continue to treat the symptom.

It should be acknowledged that the administration of Lasix doesn’t come without detriment. As a diuretic, we see horses come out of races dropped in weight and dehydrated. We see 6f sprints devastate condition and leave horses struggling to bounce back.

Horseman would say it’s simply a side effect of this life saving drug. Science would disagree as it has shown that this improvement in performance is due more because of its weight-loss effect as a diuretic than due to its minimizing the effects of that EIPH (Zawadzkas et al (2006).

And what does this do? Minimizes how often these horses can train. The average thoroughbred runs every 30-45 days, and this has been accepted as the time needed for recovery. But is it? If we remove this diuretic from our common arsenal and find our horses coming out of races in better condition, will we then see a horse who can run more often? Say every 3 weeks instead of 5.

This should encourage everyone to pause and think. More starts per year equal more races filled. More purses earned. Happier trainers, happier owners, happier track owners, and even an appeased handicapper.

We argue that horsemen should be making these decisions, because they are the ones truly assessing the horses, but are they making them for the right reasons? Do we want Lasix to treat EIPH, or to act as a diuretic and performance enhancer (Gross et al. (1999)? The horseman argue it’s for that (few and far between) horse that bleeds. The policy makers argue that its to protect PR for that (few and far between) horse that bleeds. And science would argue it’s not even that effective at one (minimizing EIPH), and yet pretty damn great at the other (increasing weight loss).

So if we put the horse first, it shouldn’t be used for either.

A disease which is over exaggerated into its detriment to the horse. A drug which masks a symptom instead of treating a disease. And a weaving and winding propaganda pitch from an industry that refuses to change.

Do I think Lasix caused the breakdowns in California? Heck no. We have shown time and time again that it improves performance, and doesn’t mask pain, and yet has become the topic of argument.

Should we still focus on the real issues leading to breakdowns? Yes. But also, we should utilize this crossroad as an impetus to make real change. Change that can affect and save our industry for the decades and centuries to come.

I am pro-horse. I am also pro-science. And at this point in time, those two things need to be at the head of this conversation. Not handicapping. Not money, greed, or propaganda.

By putting the horse first, we conquer so many battles.

We improve their health and thereby increase their ability to run.

We slash PETA and their argument that we don’t care.

And we have a sport that we can get back behind supporting and scream to the masses of our passion and love of these horses.

But until we ban Lasix, we can do none of the above. A drug that the rest of the world doesn’t need. A drug that we as Americans are clutching to with our fingertips as we dangle from the cliff our sport is falling off of. A drug that isn’t even that great at its sales pitch. And a drug that is harming our horses recovery and health after the races they run.

The conversation into what it does and why is over. The conversation into how to get it out of racing has begun. And the conversation into how this will change breeding, training, and racing needs to begin. Let’s start talking.

1. Preston, S. et al. Descriptive analysis of longitudinal endoscopy for exercise-induced pulmonary haemorrhage in Thoroughbred racehorses training and racing at the Hong Kong Jockey Club. Equine Vet J. 2015 May;47(3):366-71

2. Sullivan, S. et al. A systematic review and meta-analysis of the efficacy of furosemide for exercise-induced pulmonary haemorrhage in Thoroughbred and Standardbred racehorses. Equine Vet J. 2015 May;47(3):341-9

3. Hinchcliff, K. et al. Efficacy of furosemide for prevention of exercise-induced pulmonary hemorrhage in Thoroughbred racehorses. J Am Vet Med Assoc. 2009 Jul 1;235(1):76-82

4. Geor, R. et al. Effects of an external nasal strip and frusemide on pulmonary haemorrhage in Thoroughbreds following high-intensity exercise. Equine Vet J. 2001 Nov;33(6):577-84.

5. Zawadzkas, X. et al. Is improved high speed performance following frusemide administration due to diuresis-induced weight loss or reduced severity of exercise-induced pulmonary haemorrhage?Equine Vet J Suppl. 2006 Aug;(36):291-3.

6. Kindig, C. et al. Efficacy of nasal strip and furosemide in mitigating EIPH in Thoroughbred horses. J Appl Physiol (1985). 2001 Sep;91(3):1396-400.

7. Gross, D. et al. Effect of furosemide on performance of Thoroughbreds racing in the United States and Canada.J Am Vet Med Assoc. 1999 Sep 1;215(5):670-5.

9 Comments on “Lasix: Treating the symptom and not the disease.

  1. Excellent information. My husband is true horseman, and never used Lasix when he trained thoroughbreds. When he retired, the trainers always used the drug, even for a two year old first start. Needless to say, we won’t race again until this drug is banned.

  2. I always found it funny that in my stance against lasix that I’ve done some considerably bonehead things that according to the racing industry should have had blood gushing from my horses.
    I have raced 20 plus start horses off lasix no blood, sub par race fit horses no blood, older campaigners with 50 plus starts no blood, different surface variations no blood (all per endoscopy) …… I have tossed every variable into my strings mix and no blood. So I guess if I am to believe the hype I am exceedingly blessed to breed and buy non bleeders. Like so blessed. If only my Powerball numbers were so good.

  3. Carleigh, can you point me to any research which shows that 93% of all horses in the US run on Lasix? Are there any inferences we can make about the 7% which do not and their competitiveness against the 93% who do? Also are there differences in the ratio of those racing with Lasix versus those racing without Lasix, when comparing grass versus dirt runners?

    • Jay,

      Good questions. My number of 93% was from a few years ago. It appears that in 2018, it was actually 96% of starters ( This article does a great job at looking at raw data of what these other 4% are doing and how well.

      There is one study (Costa et al 2006) which claims that surface effects the rate of EIPH in Brazil, but I’m struggling to gain access to the full article to check the science and see if it’s sound. This paper also shows that 62% of horses experienced EIPH even after being administered Lasix.

      I will try to dig into the grass vs dirt, but haven’t seen anything on pubmed with enough horses in the study to make a huge inference on that! It actually may appear that climate has more of a role than surface!

      • Carleigh,

        Thanks for those links. I’ll keep an eye on all Joe Corajec’s articles on this matter in future.

        Is the article you refer to the one by Costa and Thomassian titled “Evaluation of race distance, track surface and season of the year on exercise-pulmonary haemorrhage in flat racing Thoroughbreds in Brazil” and published in the Equine Veterinary Journal 2006 Vol. 38, pages 487-489?

        I have a copy of the 3 page article in the Journal but assume you have read that and are looking for the full research article and source data?


  4. PREACH! Our racehorses run just fine without it. The bandaid approach is NOT worth it from an animal welfare standpoint.

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