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The Harmful Effects Of Lasix

If you’re involved with world of race horses, you’re familiar with the conflicting thoughts on Lasix, or furosemide. 

Furosemide was created to help treat and prevent bleeding lungs, or EIPH, in race horses. But many also view furosemide as a performance-enhancer, helping race horses perform better during a race. 

Is Lasix a performance-enhancer? What does furosemide really help race horses with? And what are other options for treating horses with bleeding lungs? In this article, we will delve into different harmful effects of Lasix on horse health and better alternatives for treating EIPH.

When it comes to horse health and horse supplements, you can trust the team at Vetline Equine. From our Race Today™ EIPH formula or our EqVital™ horse supplement, we are here to provide the best in horse health for both your competitive and companion horses. 

This History Of Lasix

As we already mentioned, Lasix came around as a treatment for bleeding lungs. Administering Lasix before a race can help reduce bleeding lungs in those horses. You can learn more about bleeding lungs in our post on what to do about bleeding lungs

But the opinions are mixed on whether Lasix actually helps prevent bleeding lungs during races. Regardless, a high percentage of race horses are using Lasix. In fact, in Bill Heller’s book, “Run, Baby, Run,” he explains that in 2001, 92% percent of all race horses were using Lasix. 

Studies have shown Lasix to be an effective way to prevent bleeding lungs in horses. But that doesn’t diminish the harmful effects associated with Lasix, along with the controversy over whether Lasix acts as a performance-enhancing drug. 


Lasix is administered intravenously before a race, but it also has side effects similar to a diuretic. This means that it can cause dehydration and electrolyte imbalances, along with decreased levels of blood calcium. 

These side effects can cause a horse to lose 10 to 15 liters of urine in the hour following their dose of Lasix. As common practice, many race horses are not allowed to drink water in the four hours leading up to a race, which can result in a 10–20 pound loss. 

This is where the controversy comes in. When a horse on Lasix can lose 20 pounds right before a race, does that 20 pounds handicap other race horses who are not on Lasix? 

Currently, the permissible level of Lasix that can be administered before a race is 500 mg. Studies done on the effects of Lasix say that, since the period of diuresis is short, the horses can recover from the effects associated with the diuresis. But some race horse trainers are skeptical. 

Trainer Kiaran McLaughlin is one of the signatories on a proposal that would phase out the use of Lasix in races. As he says, “It’s very interesting. For…two years, we scoped every horse after they ran and most horses after they worked to see where they stood, and I have to say that less than 5% of the horses we ran without Lasix bled at all.” 

Finding A Better Alternative 

Bleeding lungs is still something that will occur in a number of race horses. So where does that leave treatment for bleeders? 

One great alternative is Race Today™ from Vetline Equine. Race Today™ is different because it doesn’t overload race horses with natural or artificial coagulants. Instead, Race Today™ was created and tested by an equine veterinarian using vitamins and minerals that are vital for horse health, and is a feed supplement. Its purpose is to heal the lungs and make them stronger, to therefore prevent them from bleeding.

Race Today™ is a daily feed supplement that is great for all horses to use for general lung health, in addition to eliminating symptoms of EIPH. It can be given alongside lasix, however most horses never need lasix when they are consistently using Race Today. 

While there remains much controversy around the harmful effects of Lasix and its ability to enhance performance during races, there are other options to continue helping bleeders find relief. 

If you’re worried about bleeding lungs or EIPH with your competitive or companion horses, you can trust the Race Today™ formula made by Vetline Equine. Learn more about our commitment to horse health and how Race Today™ could help your bleeders on our FAQ Race Today™ page.

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