One of the more popular methods for calming horses might employ a commonly used mineral, but it’s safe only in certain applications.

Matthew Lawson couldn’t quite believe what he was hearing. He cocked his head, stuck his hands in his pockets and just nodded.

Lawson was taking over as trainer for a small private barn in Tennessee and was getting information from the outgoing trainer on the horses’ programs. “When he brought me into the barn and gave me the run-down on everything, he basically told me that the owners couldn’t ride worth a damn and that he drugged most of the horses to get them to perform well,” Lawson said.

“He told me his system of injecting magnesium sulfate solution [intravenously] to quiet a horse down or help one that maybe had a buck in him,” he added. “The way he described it to me, it was really quite horrifying. He was telling me that it had to be injected very slowly into the blood stream because if you did it too quickly, it would slow the heartbeat and cause them to die.

“At this point in the story, I was incredulous. He’d been telling his clients at the time that he was giving the horses vitamins, and he called the magnesium sulfate ‘Vitamin M.’ ”

Lawson was shocked and bewildered to think that these clients had been going to rated shows and even foxhunting a bit with drugged horses.

“I didn’t know how to react, so I just kind of nodded and went with it,” he said. “I didn’t want to throw a stick in the spokes and question it right then.”

In a conference later with the horses’ owners, Lawson quietly told them of the conversation and informed them he did not intend to continue the practice. “They were in shock. They didn’t know anything about the horses being drugged,” Lawson said.

“He was telling them that the horses got stressed at shows, so he was giving them Vitamin M to help,” Lawson added. “It’s become a little bit of a joke around here, now that the trainer isn’t in the area anymore. We joke about Vitamin M. But it’s scary to know that that kind of thing goes on.”

Not New—But Alarming

That kind of thing is definitely going on. Just as U.S. Equestrian Federation drugs and medication testing is continually expanding to identify more and more illegal medications used to alter equine performances, some riders and trainers are continually broadening the scope of their medicine trunks.

“There have been people using compounds that are detectable and undetectable to achieve sedation or calming in horses for time immemorial. As drug testing gets more and more sophisticated, efforts have moved toward compounds which have less detectable aspects to them,” said Midge Leitch, VMD, who works at the University of Pennsylvania School of Veterinary Medicine, was a former U.S. Equestrian Team veterinarian and serves on the USEF Drugs and Medications Committee.

Injectable magnesium sulfate is just one of the substances popular for use in horses now—substances that aren’t actually medications but are compounded versions of substances that occur in the horse’s body naturally. Magnesium is a mineral essential for the body’s neuromuscular function, one that acts in concert with calcium to trigger muscular contraction and relaxation. Some other such substances that are showing up in medicine trunks are calcium, thiamine and tryptophan.

“While [intravenous administration of magnesium sulfate] is getting a lot of attention at the moment, there are many things we’re worried about. We see new ways of using old medicines and new medicines being used every month. This one is just so blatant in that there’s no justified use for it via this application in the horse—that’s why it’s really easy to just say no,” said Mike Tomlinson, DVM, a former USET veterinarian and a veterinary delegate at the 2010 Alltech FEI World Equestrian Games, who serves on the USEF Drugs and Medications Committee.

Magnesium sulfate is a very common substance. The crystalline form of it is Epsom salts, which is commonly used in topical applications in equine therapy, such as soaking a foot. Magnesium is also a common ingredient in oral supplements, especially those purporting to have a calming or soothing effect.

“It’s one of the safest things we have, as long as you don’t give it intravenously,” said Tomlinson.

“Magnesium sulfate, in the form of Epsom salts, has wonderful uses topically for poultice and foot soak,” said Leitch. “And it has serious sedative properties when given intravenously. That’s obviously the intended effect, but that’s also the reason it’s potentially very dangerous. It does have the potential to produce death if given too quickly or in too large amounts.”

In human medicine, magnesium sulfate is used as an anticonvulsant and also as a tool to help manage cardiac arrhythmias. Magnesium blocks neuromuscular transmissions and depresses the central nervous system. In the book Veterinary Pharmacology and Therapeutics, injectable magnesium sulfate is listed in the “Anesthetics and Analgesics” chapter. It’s described as “producing skeletal muscle relaxation,” and when used as an anesthetic agent, produces death by asphyxiation.

In fact, magnesium sulfate used to be an ingredient used in anesthetizing horses. “There’s absolutely no medicinal intravenous use of it, and that’s why we’re concerned about it,” said Tomlinson. “There is no intravenous use in a horse—especially ones that are competing—unless you are anesthetizing it.”

No Margin For Error

It might seem that magnesium sulfate isn’t as dangerous a substance as, say, an opiate tranquilizer, since it’s a mineral used by the horse’s body, in normal function, but any imbalance of such a substance can have devastating effects. The 21 polo ponies that dropped dead before a match in 2009 were shown to have died because of a toxic overdose of selenium, another substance that is used in normal bodily function.

“Any number of these individual compounds are non-toxic but can produce toxic results, even death, when given in excess,” said Leitch. “With pretty much all of them, you walk a thin line between creating the sedation you hope for and a seriously toxic effect.”

And the margin of error is tight, which makes it all the more dangerous if anyone other than a veterinarian is deciding on dosages and administering magnesium sulfate intravenously.

“We don’t have much research, but I can say anecdotally that the margin of error is really small. It’s not like there’s a 10x safety dose. In order to have the sedative effect, you are basically what we call in anesthesia halfway killing them. The difference between halfway and all the way isn’t very far. Even if you’re a vet, it’s very easy to misjudge that,” said Tomlinson.

Rumors abound about horses collapsing and/or dying from the effects of intravenous magnesium sulfate administration, but there’s no official record of such incidents, and—if they occur—they’re covered up quickly.

“It’s like reporting a robbery at a drug buy—nobody comes out and tells you,” said Tomlinson. “There are anecdotal stories of people saying, ‘This horse dropped dead in its stall right before the class.’ Of course, everyone says, ‘Oh, it had a heart attack.’ But horses don’t die of heart attacks. So all we can say is there are horses which have died after getting injections that are referred to as ‘just a vitamin.’ ”

Playing With Fire

Juan Gamboa, DVM, who has a thriving horse show practice, is so concerned about the use of injectable magnesium sulfate that he distributed a memo to his clients:

“Magnesium sulfate has been used for many years to help calming a horse. I want you to understand the risk of this drug when given intravenously. Magnesium sulfate directly affects the heart, forcing it into a state of arrhythmia. When used in larger doses, it can shut down cardiac function, result in subsequent collapse of the horse, and in some cases, death may occur. If accidentally given intra-carotidal, the results are immediate and very dramatic, causing the horse to convulse, sometimes flip backwards and then collapse. This may be fatal, not only to the horse but to anyone in the surrounding area. If given peri-jugular, it may cause severe jugular inflammation, and sometimes complete destruction of the vein. I have used magnesium sulfate (Epsom salts) as a laxative and to stimulate horses to drink water during the horseshow and at home. This decreases the chances to develop impactions. One beneficial side effect is the calming effect that magnesium provides, but I emphasize, it is given orally and the intention is to stimulate water consumption. According to the USEF, any medication used to quiet a horse violates the spirit and the intent of longstanding USEF rules. No medication nor supplement will replace a good and conscientious training program for the discipline you are participating in.”

Gamboa does not condone the use of intravenously administered magnesium sulfate, and he refuses to administer it for clients. “I’ve been asked to do it, but every time, I talk to them and say, ‘I don’t like the use of magnesium sulfate; we need to do something different,’ ” he said. “But I do see it is happening. I understand why people are doing it. They want their horses to perform at the horse shows, and they need them to relax a little bit. Injected magnesium sulfate alone, or combined with calcium, has a calming effect on horses.

“I haven’t seen this myself, but I have heard that horses have had bad reactions to the injections. I’ve never seen one die, but I’ve heard of horses lying down, having convulsions, and then getting back up. If you’re injecting it, you’re playing with fire,” he added.

He recommends that his clients instead use magnesium as an oral supplement. “It’s safe and easy to use. Does it work? Maybe. I think that sometimes it’s in the minds of the people that it works, but some people swear it works. I don’t have any problem with oral administration, but I do have a problem with injectable,” said Gamboa.

It’s Just Not Right

Since it’s a naturally occurring substance in the body, magnesium sulfate delivered via intravenous administration is difficult to detect through medication testing.

“Magnesium sulfate has no traceable component,” said Leitch. “It is readily and easily dealt with by the body. Applying a testing procedure would have to be done in a very timely fashion, likely within very short periods of time within administration, and you can imagine the complexity of getting that done.”

USEF rule GR410.1 reads:

No horse and/or pony competing in a Breed or Discipline designated as (or part of) a Therapeutic Substance Group is to be shown in any class at a competition licensed by the Federation (see also GR402.1, last sentence) if it has been administered in any manner or otherwise contains in its tissues, body fluids or excreta a forbidden substance except as provided in GR411. Any horse and/or pony that competes in more than one Breed, Discipline, and/or Group at a competition, one of which is a No Foreign Substance Group, shall be required to be in compliance with the No Foreign Substance Provisions at all times while competing in any and/or all classes and/or divisions at that competition. For purposes of this rule, a forbidden substance is:

            a. Any stimulant, depressant, tranquilizer, local anesthetic, psychotropic (mood and/or behavior altering) substance, or drug which might affect the performance of a horse and/or pony (stimulants and/or depressants are defined as substances which stimulate or depress the cardiovascular, respiratory or central nervous systems), or any metabolite and/or analogue of any such substance or drug, except as expressly permitted by this rule.

Given that, administered intravenously, magnesium sulfate acts to depress the central nervous system and block neurotransmission, its use in horses competing in USEF-recognized shows is clearly illegal.

“I think it’s virtually impossible to know how widespread its use is. Nobody’s going to fess up to giving it, be they veterinarians or trainers or whoever. But it’s clearly not in the spirit of the regulations,” said Leitch.