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What Does Lasix Do For A Racehorse?

Lasix, also known as Furosemide, is a prescription medication used to treat fluid retention and high blood pressure in horses. It is a powerful diuretic, meaning it increases the amount of urine your horse produces. Lasix is commonly used in horse racing to prevent horses from bleeding from the lungs during intense exercise.

How Does Lasix Work?

Lasix works by blocking the reabsorption of salt and water in the kidneys. This causes the horse to produce more urine, which helps reduce the amount of fluids in the body. Lasix also helps reduce the amount of blood that passes through the lungs during exercise, which can reduce the effects of exercise-induced pulmonary hemorrhage (EIPH).

What Are the Benefits of Lasix for Racehorses?

The primary benefit of Lasix for racehorses is that it can help prevent EIPH. EIPH is a condition where the blood vessels in the lungs become damaged due to the intense exercise of racing. This can result in a decrease in performance and, in extreme cases, can even be life-threatening. By reducing the amount of fluids in the body, Lasix helps reduce the risk of EIPH.

Lasix can also help horses perform better by increasing the amount of oxygen they can take in. When there is less fluid in the lungs, it allows more oxygen to be taken in, which can improve performance.

What Are the Side Effects of Lasix?

While Lasix is generally considered safe for horses, there are some potential side effects that can occur. These include:

  • Dehydration – Because Lasix increases the amount of urine a horse produces, it can lead to dehydration if not monitored and managed properly.
  • Electrolyte Imbalance – Lasix can cause an electrolyte imbalance in the horse, which can lead to muscle cramping, weakness, fatigue, and other problems.
  • Decreased Appetite – Lasix can also cause a decrease in appetite, which can lead to weight loss.
  • Liver Damage – If used over a long period of time, Lasix can damage the liver.

What Are the Alternatives to Lasix?

If you are concerned about the potential side effects of Lasix, there are some alternatives that can be used to help reduce the risk of EIPH. These include:

  • Electrolyte Supplements – Electrolyte supplements can help restore electrolyte balance in the horse, helping to reduce the risk of dehydration.
  • Omega-3 Fatty Acids – Omega-3 fatty acids have been shown to reduce inflammation in the lungs and can help reduce the risk of EIPH.
  • Herbal Supplements – Herbal supplements, such as nettle, dandelion, and ginger, can help reduce inflammation and improve performance.
  • Respiratory Support Supplements – Supplements such as Vitamin E and Vitamin C can help support the respiratory system and can help reduce the risk of EIPH.
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When Should Lasix Be Used?

Lasix should only be used when absolutely necessary. It should not be used for every race, as it can cause serious side effects if used too often. If your horse is showing signs of EIPH, then Lasix may be necessary. However, it is important to weigh the risks and benefits before administering Lasix to your horse.

What Are the Guidelines for Administering Lasix?

If your horse is showing signs of EIPH or is at risk of developing EIPH, your veterinarian may recommend administering Lasix. If this is the case, there are some guidelines that should be followed:

  • Lasix should be administered at least two hours before a race.
  • It should be administered at a rate of no more than 500 mg per day.
  • It should not be administered more than three days in a row.
  • It should not be administered more than four times in a month.
  • It should not be administered more than six times in a racing season.

What Are the Rules Regarding Lasix?

Lasix is a regulated substance and is subject to rules and regulations by the governing bodies of horse racing. In the United States, the use of Lasix is regulated by the Association of Racing Commissioners International (ARCI).

The ARCI has issued the following rules and regulations regarding the use of Lasix:

  • Lasix must be administered by a veterinarian.
  • Lasix must be administered according to ARCI guidelines.
  • Lasix must be administered within the two-hour window before the race.
  • Lasix must be administered in a designated area, such as a barn or tack room.
  • The horse must be monitored for adverse reactions after the administration of Lasix.
  • If the horse experiences any adverse reactions, the race must be cancelled and the horse must be given appropriate treatment.


Lasix is a powerful diuretic that can be used to help reduce the risk of EIPH in racehorses. It can also help horses take in more oxygen, which can improve performance. While Lasix is generally considered safe, there are potential side effects that can occur, so it should only be used when absolutely necessary. Additionally, it is important to follow ARCI guidelines when administering Lasix to ensure the health and safety of the horse.


  • “Furosemide (Lasix).” Merck Veterinary Manual, Merck & Co., Inc., 2020, www.merckvetmanual.com/pharmacology/diuretics/furosemide-lasix.
  • “Understanding EIPH (Exercise Induced Pulmonary Hemorrhage).” Kentucky Equine Research, Kentucky Equine Research, 2016, www.ker.com/library/understanding-eiph-exercise-induced-pulmonary-hemorrhage/.
  • “Lasix for Horses.” Horse Health USA, 2017, www.horsehealthusa.com/horse-articles/lasix-for-horses.
  • “ARCI Model Rules, Chapter VI, Section 6.17.” ARCI, ARCI, 2018, www.arci.com/model_rules/chapter_VI.html#6_17.