Veterinary pharmacologist Dr. Trisha Dowling: “If you’re competing in a horse sport, the first thing you need to know is whose rules you’re running under.
Veterinary pharmacologist Dr. Trisha Dowling: “If you’re competing in a horse sport, the first thing you need to know is whose rules you’re running under."

Drugs in my tack box

Much like human sport competitions, irresponsible medication use and a positive drug test can cause serious problems for both the horse and rider at equine events.

"If you're competing in a horse sport, the first thing you need to know is whose rules you're running under," says Dr. Trisha Dowling, a board-certified specialist in veterinary pharmacology and large animal internal medicine at the Western College of Veterinary Medicine (WCVM). The veterinary professor is also a member of the Equine Medications Committee for Equestrian Canada (formerly known as Equine Canada).

Equestrian Canada (EC) is responsible for many equine competitions on a national level, but international disciplines such as reining and show jumping can be sanctioned under the Fédération équestre internationale (FEI). Many Canadian competitors also travel south of the border where the U.S. Equestrian Federation (USEF) organizes many of the competitions. Medication rules vary considerably between these regulatory bodies.

Historically, organizations preferred a "no drug" rule (also known as the "oats, hay and water" rule) — meaning that the horse competed solely on its own natural talents without any chemical help.

However, as analytical chemistry has improved, the equine drug testing laboratories are able to detect extremely small amounts of drug in blood or urine samples from horses. Most drugs are readily detected in the parts per billion — some even in the range of parts per trillion.

"Clearly these minute traces of drug are not causing performance-altering effects and calling positives at this level is detrimental to the welfare of the horse," says Dowling. "As veterinarians, we need to use medications for valid therapeutic purposes, and we still want people to be able to compete when the drug is no longer affecting the horse."

Many horse sport organizations use a "threshold rule" that recognizes the use of certain drugs with legitimate uses such as certain non-steroidal anti-inflammatory drugs (NSAIDs), tranquilizers and local anesthetic drugs. Some of these medications may affect the horse's performance, but they have a valid use in veterinary medicine. In these cases, sport organizations set threshold concentrations in blood and/or urine, and a drug violation would only occur if the medication in the horse exceeds the set threshold.

"To set a threshold, we need to do studies to determine what we care about and what we don't," says Dowling. "If it's something that shouldn't be in a horse, such as cocaine, then we set the threshold at the lowest amount that our laboratory is able to detect — but this can still cause problems from inadvertent contamination."

For example, Dowling points to a case that was recently described in a Canadian Veterinary Journal article.

"A horse trainer got a good deal on a used horse trailer, not knowing that it had been used as a mobile meth lab," she says. "After using it to haul horses to the races, he ended up with all of the horses testing positive for low levels of methamphetamine from contact with contaminated surfaces in the trailer."

If a prohibited drug is detected in a horse during competition, EC applies the violation to the person who signs the entry form and declares responsibility for the horse. The person must be an EC member and be over the age of 18. Penalties are assigned to the violation based on a classification system used by racing to assess the severity of the infraction. For example, penalties are more severe for the use of tranquilizers than for the use of anti-inflammatory drugs.

EC does offer an emergency provision to competitors if it is medically necessary to use a prohibited drug near the time of competition. For example, if a horse is injured while being transported to a show or during a competitive event, EC allows the use of emergency medicine such as a local anesthetic or a tranquilizer drug.

A veterinarian must administer the medication and complete an equine emergency medication report form (available on the Equestrian Canada website) that must also be filed with the competition steward. The horse must also be withdrawn from competition for 24 hours.

Dowling advises purchasing approved veterinary drugs that have a drug identification number (DIN) because it means that the drug is produced by a licensed pharmaceutical company and has been subjected to stringent quality control, which lowers the risk of contamination.

She strongly advises against the use of compound drugs since these products are made by pharmacies — not by pharmaceutical companies. As Dowling points out, drugs are only supposed to be compounded to fulfil a specific patient need, such as when the approved drug formulation isn't suitable for a specific patient. However, compounded drugs are sometimes made in large batches and sold at cheaper prices than the approved drug without undergoing the strict manufacturing processes that a pharmaceutical company must follow.

Numerous studies have also shown that compounded equine products may contain less drug than labelled that could lead to treatment failure. Or, the product could contain more drug than labelled — potentially causing a toxicity.

In addition, Dowling generally advises against feeding supplements to horses.

"Supplements are not drugs; they don't have DIN numbers and do not necessarily meet the same manufacturing standards as a drug. At best, they're often a waste of money, but they can also be a reason for a violation when they are contaminated with substances that cause a positive test," she says.

"If a product claims to calm your horse down or make it have bigger muscles, that's pretty much impossible to do without using a prohibited substance."

Feed contamination is another problem facing horse owners, especially when horse feed is purchased from a mill that produces feed for other types of livestock. The mill's equine products can become contaminated with chemicals or drugs that are used in cattle, poultry and swine feed.

Horse owners can avoid problems by buying their horse feed from an equine-only feed mill, but it's still not complete insurance against contamination.

"Your best defence is to keep samples of your feed, so if you receive a violation, the samples can be tested to confirm it was contaminated feed," says Dowling.

Contamination can also occur between horses through shared feed buckets and stalls — especially at horse shows. Dowling advises thoroughly cleaning your show stall before using it and bringing your own non-porous feed buckets. She adds that owners and riders need to be very careful about who is around their horse since drug contamination can easily occur between people and horses.

Many violations are simply caused by human error, says Dowling. For instance, the drug administrator can incorrectly calculate the therapeutic drug dosage, change the method of administration, give medication to the wrong horse, or give the drug too close to the actual competition.

If owners are planning to use a drug that's not permitted by the event's organizing body, they need to clearly understand when the treated horse can enter a competition by reviewing the specific medication's withdrawal times with the prescribing veterinarian. To assist veterinarians and competitors, the Canadian Pari-Mutuel Agency publishes a guidebook on drug detection times (available on the EC website). EC follows the same guidance except for the permitted drugs where no withdrawal is necessary.

For valid therapeutic medications, the guidebook lists a dose and detection time. But Dowling stresses that a detection time is not a withdrawal time; it's a statistically-determined time that the laboratory can detect the drug, and it was determined in a small number of horses.

As a horse's age, sex and diet can influence how long the drug can be detected in its system, a veterinarian with knowledge of the horse should determine the withdrawal time used before competition. In general, Dowling says the EC Equine Medications Committee recommends doubling the listed detection time to use as a withdrawal time.

EC posts the permitted medications in the rules on its website, and Dowling urges caution when administering any non-permitted drug to your horse before a show.

"If it's not permitted, consider it prohibited," she says. "And always consult with your veterinarian regarding medication use and appropriate withdrawal times for your horse."

Visit to view Equestrian Canada's equine medications control rules.

Reprinted with permission from Canadian Horse Journal ( and the WCVM Townsend Equine Health Research Fund (

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