Lasix in Horse Racing: To Be or Not To Be

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Mel Daniels

February 7th, 2015

Lasix is a diuretic that increases urine productions and frequency. It has been given to horses for decades in the U.S. as a way to reduce or prevent nose bleeds. There is a noticeable speed increase when a horse uses Lasix. It is most noticeable when the horse is using it for the first or second time.  Not only does Lasix help with urine production, it also lowers blood pressure in the lungs. The effects last around 3 to 4 hours.

There is a push to incrementally phase out Lasix in the United States, prohibiting use in two year old races, with a view to expand the ban in all races. The proposal was endorsed by 25 trainers including top trainers Todd Pletcher and Richard Mandella.


Why do horses bleed?

Racehorses are unique in that they are one of very few animals to suffer exercise induced pulmonary hemorrhage. When you take a horse out to exercise or race it, the blood pressure from the right side of the heart to the lungs increases around 75% more.When a horse bleeds, the severity is graded from 0 to 4.
  • 0 = The horses lungs show no visible signs of bleeding.
  • 1,2 and 3 = There is a varied amount of blood in the lungs, but no signs of bleeding through the nostrils.
  • 4 = Blood is visible in either one or both nostrils.


In Australia, if a horse is found to have bled after a race, the horse is not allowed to race again for three months. If a second bleeding occurs, the horse is banned for life from racing.

There is much debate about this drug. Is it unfair for a horse to be on Lasix against horses that are not?
  • If you ban Lasix in the United States, what rules shall imply if a horse bleeds?
  • Will it diminish the fields in races which are already getting smaller and smaller?
  • What would a ban on Lasix mean to the horseplayer?
  • Would it make handicapping easier or more difficult?
  • It will be very nice to hear other Bet America players feedback on this matter.  Please leave your comments below.

More Reading:

Lasix: the drug debate which is bleeding US horse racing dry  (The Guardian, UK, August 2014)

Stronach urges racetracks to ban race-day Lasix (DRF, August 2014)

Breeders’ Cup Lasix study yields ‘suprising’ results (Paulick Report, December 2013)

The great Lasix debate - How well is it understood?  (, Australia, January 2015)