As post-performance drug testing methods become more sensitive, racehorse and show horse owners, veterinarians, handlers, and trainers have become more aware that positive drug tests could be the result of inadvertent contamination of the horse with chemicals present in the environment. Cynthia Kollias-Baker, DVM, PhD, director of the Racing Laboratory at the University of Florida, recently reviewed possible environmental sources of drug positives and presented her findings at the 2002 American Association of Equine Practitioners Convention.

Kollias-Baker told racehorse and show horse practitioners that this topic will be a continual problem in the future. "In racing today and in show horses, we consider the trainer to be 100% liable for that horse--they need to control everything the horse is exposed to," she said. She and other researchers have been looking into what levels of inadvertent exposure can cause positives test, and what physiological effects those contamination levels have in the horse.


Baker's first drug to review was cocaine, a substance which is highly addictive, and that has both local anesthetic and psychostimulatory effects. In both humans and horses, cocaine is metabolized or broken down to form benzoylecgonine (BZE) and ecgonine methyl ester (EME), which are found in urine.

"I was skeptical that a small amount of cocaine could cause positives in horses," said Kollias-Baker. When four horses were given 2.5 mg of cocaine sublingually (under the tongue), urine samples contained detectable concentrations of BZE for up to 24 hours post-administration. She emphasized that this small amount of cocaine could conceivably be the amount of powder left on an abuser's hands.

Administration of this small amount of cocaine caused no detectable effects on the horse, but higher doses in the range of 50 mg, when administered intravenously (IV), caused a transient, brief decrease in heart rate, which returned to normal after about a minute. Based on previous reports in the scientific literature, she expects that you would have to administer 100mg intravenously to a horse before there would be a demonstrative effect on the horse's behavior and possibly an effect on performance. 

In addition, although no central nervous system (CNS) effects or persistent or long-lasting cardiovascular effects were noted after IV administration of 50 mg of cocaine, the urinary concentrations of BZE and EME were far in excess of those occasionally found in urine samples collected after races and show events.


Morphine is a naturally occurring alkaloid found in the opium poppy Papaver somniforum, which is native to the Far and Middle East. The plant is cultivated throughout the world, and parts of it are commonly imported for baking.

Opiate agents are only used occasionally in horses because they can cause undesirable CNS stimulation. According to Kollias-Baker, you can use opiates in the horse and they will have an analgesic effect.

 "The presence of any opiate at any concentration in post-race urine samples is of concern to racing authorities because in the past, these drugs have been administered to horses in illicit attempts to enhance their racing performances," she said in her paper.

She referenced two studies where morphine was detectable for up to 24 hours in urine samples collected from horses after 1-10 grams of poppy seeds were fed to the horses.

Analytical findings of morphine could also result from illegal opiates such as heroin and prescription medications such as codeine.

Kollias-Baker explained that when laboratories analyze samples, they have no way of knowing if a morphine positive is from feeding the horse a poppy seed muffin or bagel, inadvertent feeding of bakery byproducts that are sometimes used in the preparation of animal feeds, contamination from a drug used by someone handling the horse, or deliberate administration as a performance enhancer.

"I have no way of differentiating,” said Kollias-Baker. “One cannot assume that every positive is a purposeful administration."

Therapeutic Medications

Recent studies have shown that environmental sources of non-steroidal anti-inflammatory drugs (NSAIDs) can result in positive drug tests.

Kollias-Baker gave the example of a horse which tested positive on a urine test for ibuprofen after consuming feed prepared by an individual with ibuprofen gel on his hands. Another study showed that untreated horses housed in stalls previously occupied by horses treated with therapeutic doses of flunixin (Banamine) had detectable concentrations of flunixin in their urine for up to 14 days (see article #1002 at Agents that are used in long durations of therapy might linger in the horse's environment at high concentrations. In one study, after a 10-week treatment period with isoxsuprine, scientists were able to detect the agent in various parts of a horse's stall and grooming materials for weeks after the last treatment was administered to the horse.

Good barn hygiene was emphasized to prevent environmental contamination of racehorses or show horses.


Numerous post-race analytical findings for prohibited substances have been attributed to consumption of contaminated nutraceuticals or herbal products.

Kollias-Baker said those who do drug testing have been very attuned to these products, especially herbal ones. "These products don't have to meet the same FDA standards that other (products) do. You need to warn your owners and trainers. Even if (the label) says they won't test (positive), you have no idea if the next batch will be contaminated. You don't know what is actually going to be in those products."

She recalled her laboratory identifying an herbal supplement that contained ephedrine, a drug commonly used in cold remedies, that is a prohibited substance in most competition horses because it causes central nervous and cardiovascular stimulation.


These agents are best known for their mild stimulatory effects on the central nervous system, but they also have other systemic effects such as bronchodilation and diuresis. Caffeine, theobromine, and theophylline fit this category, Caffeine has been shown to enhance certain types of athletic performance in humans, so regulators have often viewed the finding of even small amounts of these agents in equine urine samples as serious rule infractions. Kollias-Baker reminded veterinarians that caffeine is pervasive in the horse's environment--coffee, chocolate, sodas, and tea all contain caffeine and theobromine.

"The key is educating your clients" to prevent inadvertent positives, she explained. In one study, "10 peanut M&Ms made one horse test positive," she said.

Atropine and Scopolamine

Kollias-Baker talked about two more agents that are sometimes found in the horse's environment and can cause positive drug tests.

Datura sp. are a group of plants, which includes Jimson Weed, that are bitter tasting because they contain a number of different chemicals called alkaloids. These plants can be harvested with grain and hay, but also grow in and around stables and pastures. The best described of these chemicals are scopolamine and atroprine. While both of these compounds are alkaloids, they have different effects in the body. Scopolamine is commonly used to prevent motion sickness in humans and is applied using a small patch that is placed behind the ear.

Atropine is used occasionally as a bronchodilator in horses, but one of its side effects is a decrease in gastrointestinal motility which can cause colic. "Although horses will rarely willing consume enough of these plants to make themselves sick, just a mouthful can cause a positive urine test for either of these agents" said Kollias-Baker.


The key to avoiding inadvertent positives from environmental contaminants is client education, Kollias-Baker told her veterinary audience. "There are a plethora of compounds out there that could hurt your client," she said. "Owners can keep their barns clean, and keep horses that are being medicated separated as much as possible from non-treated ones."

She listed some key prevention measures that owners can take:

  • Be aware of the risks for inadvertent contamination;
  • Keep accurate records for every horse being treated with any type of medication;
  • Grooms and handlers should wash their hands between treating one horse and handling another;
  • Stalls and feed buckets should be cleaned thoroughly whenever occupants change and after therapy with non-permitted medications;
  • Human food items (i.e., candy, coffee, soda, or bakery goods) should not be fed to horses which are subject to drug testing;
  • Herbal remedies and nutraceuticals might contain non-permitted substances--be aware of that fact and use these products with great care.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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