What is the Lasix Controversy in Horse Racing?

If you are betting online on horse racing and specially on US races, you may have heard of something called “Lasix.”  The very idea of race-day medications may very well seem bizarre, but it is one thing which sets US horse racing apart from horse racing in the UK or pretty much anywhere else.

What is Lasix?  Also called Salix, it is an anti-bleeding drug.  As a diuretic, it flushes out excess fluids, lowering a horse’s blood pressure and reducing internal bleeding in turn.  It originally became legal to use in the US in the 1970s.  Gradually it became legalised throughout the 50 states.  By 1995, it was legal everywhere (New York was the last state to legalise Lasix).

Lasix is controversial for multiple reasons.  For one, it is a race-day medication, which in itself is a problematic consideration.  For another, people who believe horse racing is cruel use Lasix as part of their argument.  If horses need a medication like Lasix to stop internal bleeding while they are racing, these people argue, then those horses are already being pushed too hard in the first place.

The majority of horses do bleed to some degree when they are running hard in a race, but only a very small percentage bleed so severely that they need a medication like Lasix. 

Why do horses bleed internally when they run?  Professor Ken Hinchcliff explains it like this: “If you take a horse out and exercise it, then the blood pressure leading from the artery on the right side of the heart to the lungs increases from about 25mm of mercury [pressure] to about 100mm of pressure” . “You don’t see anything like this in humans, for example.”

This means that the capillaries in a horse’s lungs may rupture, causing bleeding.  The bleeding may be graded on a scale of 0-4.  Four is of course the worst and is referred to as “epistaxis.”  It is estimated that around 0.1%-0.2% of starters experience epistaxis.  The condition can cause sudden death, but it is very rare.  Biologists say that there are no pain receptors which would register epistaxis as a painful event—it would feel more like how you do if you have mucus in your lungs.

If a horse bleeds at a 2-4 on the scale, that horse’s performance is compromised.  Lasix allows horses in these circumstances to compete in races in which they would otherwise not be able to run.

As you might guess, the other concern with Lasix is whether or not it should be considered a performance-enhancing drug.  There are a couple of concerns here:

• Lasix could be used to mask other drugs (this is one of the reasons it is banned in the UK).
• Sometimes horses race better the first or second time they receive Lasix in a race (important to know if you are handicapping a US race).

Another thing which may interest you is that Lasix is not entirely banned in the UK.  It is only banned as a race-day medication.  It is actually allowed during training.  Many trainers still avoid using it, indicating that they do not have many problems, and believe that it may simply be that racing conditions in the US cause more bleeding than racing conditions in the UK.

Is Lasix good or bad for horses?  Is it good or bad for horse racing?  It is up to you to form your own opinion, but what is most important for you to know as a handicapper is that it is a factor in US races, but probably not something you will encounter anywhere else.  If you discover a horse is going to be on Lasix for the first or second time in a US race, that horse may enjoy a temporary performance boost.  Otherwise, assuming Lasix is not being used to mask other performance drugs, it probably will not have a noticeable impact.