Last updated: May 27, 2026
A few years ago I attended a quarterly meeting of the Louisiana Horse Racing Commission. The room was full of trainers whose horses had failed drug tests — not just first-time offenders, but many who had been caught multiple times. The number of repeat violations was the most striking thing in the room. These were people who had been suspended, paid fines, and come back and done it again. That meeting shaped how I think about PEDs in racing: the problem is not ignorance, it is incentive structure.
Performance-enhancing drugs in horse racing — what you need to know:
- Most common PED categories: anabolic steroids (muscle mass), blood-doping agents (oxygen capacity), stimulants (alertness), diuretics (weight and masking), and pulmonary drugs (breathing)
- Most controversial legal drug: Furosemide (Lasix), used to treat exercise-induced pulmonary hemorrhage — permitted in the US, banned in most other countries
- Emerging threat: Zilpaterol, a muscle-growth agent primarily used in Quarter Horse racing — An LSU veterinarian warned that the cardiovascular and musculoskeletal damage associated with the drug could dramatically shorten a horse’s racing career and long-term survival.
- Regulatory shift: HISA (Horseracing Integrity and Safety Authority) created a uniform federal standard in 2023, replacing the previous patchwork of 38 different state rules
- Key case: Medina Spirit, 2021 Kentucky Derby winner, disqualified after testing positive for betamethasone; trainer Bob Baffert received a suspension and Mandaloun was named the official winner
About this guide: Observations from the Louisiana Horse Racing Commission meeting, the Zilpaterol briefing from an LSU veterinarian, and ownership experience at Fair Grounds, Delta Downs, and Evangeline Downs inform the practical sections. Regulatory information draws on published HISA guidelines and racing commission records.
Table of Contents
A Brief History of PED Use in Horse Racing
The use of substances to alter horse performance predates any modern regulatory framework. In 1897, The Jockey Club introduced rules against doping — not primarily to protect horse welfare, but to protect the integrity of wagering. The financial stakes of race outcomes had grown large enough that cheating through stimulants was threatening the betting market’s legitimacy. Cocaine, strychnine, and morphine were among the substances most commonly used to alter performance in those early years.
By the 1940s, most tracks had implemented saliva and urine testing protocols. These were primitive by modern standards but caught the most commonly used compounds of that era. The 1960s and 1970s brought anabolic steroids into racing. The 1980s and 1990s introduced blood-doping agents. Each technological shift in PED chemistry was followed by a lag in detection capability — a pattern that continues today.
The most prominent modern case involved Medina Spirit, the 2021 Kentucky Derby winner, who tested positive for betamethasone — a corticosteroid with anti-inflammatory properties. Trainer Bob Baffert received a 90-day suspension and a $7,500 fine from the Kentucky Horse Racing Commission. Medina Spirit was disqualified and Mandaloun was named the official 2021 Kentucky Derby winner. The case accelerated the push toward federal regulatory reform that eventually produced HISA. In 2020, separately, the United States Southern District of New York indicted 27 trainers for coordinated PED use — the largest federal prosecution in the sport’s history.
Types of Performance-Enhancing Drugs Used in Horse Racing
PEDs in horse racing fall into several distinct categories, each targeting a different aspect of equine performance. Understanding the mechanism of each type helps explain both why trainers use them and why detection is difficult.
| Category | How It Works | Examples | Status |
|---|---|---|---|
| Anabolic steroids | Synthetic testosterone variants — increase muscle mass, strength, and recovery rate; can mask injuries | Stanozolol, Nandrolone, Boldenone, Trenbolone | Prohibited in all major jurisdictions |
| Blood-doping agents | Increase red blood cell count, raising oxygen-carrying capacity and aerobic endurance | EPO, blood transfusions, hemoglobin-based carriers | Prohibited; detection has improved significantly since 2010 |
| Stimulants | Increase alertness, mask fatigue, and raise heart rate and energy output | Caffeine (above threshold), theobromine, amphetamines | Prohibited above threshold levels |
| Corticosteroids | Reduce inflammation; can mask lameness and allow horses to run through pain | Betamethasone, dexamethasone, triamcinolone | Permitted therapeutically with withdrawal windows; Medina Spirit case involved betamethasone |
| Diuretics | Increase urine output, reducing weight and — critically — flushing other prohibited substances from the system faster | Furosemide (Lasix), hydrochlorothiazide | Furosemide permitted in US for EIPH-diagnosed horses; banned in most other countries |
| Pulmonary / bronchodilators | Open the airways, improving oxygen intake during intense exercise | Clenbuterol, albuterol | Controlled; Clenbuterol is a known masking agent and under stricter limits since 2019 |
| Muscle-growth agents | Beta-agonists that promote rapid muscle development; used primarily in Quarter Horse racing | Zilpaterol, ractopamine | Prohibited in racing; Zilpaterol cases have sharply increased at Louisiana Quarter Horse meets |
Anabolic Steroids — The Most Common Category
Anabolic steroids remain the most widely detected class of PEDs in horse racing worldwide. Their appeal is straightforward: they increase muscle mass, improve recovery between workouts and races, and can reduce the severity of minor injuries enough that a horse continues competing when it should be rested. The masking effect on injuries is arguably more dangerous than the performance enhancement — a horse that should be pulled from training continues to work because the pain signal is suppressed, accumulating damage that eventually produces a catastrophic breakdown.
This video covers the Bob Baffert case and the broader debate about how racing’s regulatory bodies handle repeat violations.
Furosemide (Lasix) — The Legal Drug That Divides the Sport
No drug in horse racing generates more legitimate debate than furosemide, sold under the brand name Lasix. It is a diuretic used to treat exercise-induced pulmonary hemorrhage (EIPH) — a condition where a horse’s lungs bleed during intense exercise. EIPH is genuinely common in racehorses, and furosemide genuinely reduces its severity by lowering blood pressure in the pulmonary vessels during peak exertion.
The controversy has two parts. First, furosemide causes horses to urinate heavily before a race, reducing body weight by 20 to 30 pounds — a meaningful performance advantage at race pace that exists independent of any EIPH treatment benefit. Second, the drug’s diuretic effect accelerates the clearance of other prohibited substances from a horse’s urine, potentially masking violations that would otherwise be detected. These concerns have led most international racing jurisdictions to ban furosemide entirely. The United States continues to permit its use, with horses required to receive the drug no more than four hours before a race under veterinary supervision.
The Lasix debate in practice: Most American horsemen argue that banning Lasix would cause real suffering in horses with genuine EIPH diagnoses. Most international regulators counter that the weight-loss and masking effects create an unfair advantage and undermine testing integrity. Both sides have legitimate points, which is why the debate has persisted for decades without resolution. HISA has moved toward restricting race-day Lasix use in stakes races, signaling a gradual shift toward the international position.
Zilpaterol — The New Threat in Quarter Horse Racing
At the Louisiana Racing Commission meeting I attended, Zilpaterol was the drug appearing most frequently in positive tests — and every case involved a Quarter Horse trainer. Zilpaterol is a beta-agonist originally developed for use in cattle to promote rapid muscle growth before slaughter. Its application in horse racing is a direct transfer of that mechanism: trainers are using it to add muscle mass and improve short-distance sprinting power in Quarter Horses, where races are decided over 220 to 440 yards and raw explosive strength is the primary determinant of outcome.
What an LSU veterinarian told me about Zilpaterol: I spoke with a veterinarian from LSU after the commission meeting to understand the health implications. His assessment was direct: the drug causes severe cardiovascular and musculoskeletal damage, and horses that receive it are likely to sustain permanent and life threatening damage. The mechanism that produces rapid muscle growth also stresses cardiac function and connective tissue in ways the horse’s system cannot sustainably handle. The trainers using it are not just cheating — they are destroying the horses they are supposedly trying to win with.
The Zilpaterol cases at Louisiana meets represent a broader pattern in Quarter Horse racing, where the extreme short-distance format creates particularly strong incentives for muscle-enhancing agents. The sport’s governing bodies have been slower to develop detection protocols for newer beta-agonists than for traditional anabolic steroids, which has allowed Zilpaterol use to spread before testing caught up with it.
HISA and the Move Toward Uniform Federal Regulation
Before 2023, horse racing in the United States operated under 38 different sets of state racing commission rules — meaning a substance banned in Kentucky might be permitted in Louisiana, and a trainer suspended in one jurisdiction could simply move to another. This patchwork created systematic opportunities for regulatory arbitrage that sophisticated bad actors exploited routinely.
The Horseracing Integrity and Safety Authority (HISA) changed that structure fundamentally. HISA established a uniform federal anti-doping and medication control program that applies to all Thoroughbred racing in the United States. The program standardizes prohibited substance lists, testing protocols, withdrawal times, and penalties across every state simultaneously. A trainer suspended under HISA cannot simply move to a different state’s jurisdiction to continue racing.
For owners and bettors, HISA represents the most significant structural change in American racing integrity in the sport’s history. For the trainers in that Louisiana commission meeting room — the repeat offenders who had bounced between jurisdictions — it represents a genuine shift in consequences. The penalties for violations under HISA are also generally more severe than what most state commissions were imposing, with five-year suspensions now realistic outcomes for serious violations.
Challenges That Remain
HISA addresses the jurisdiction problem but does not solve the underlying incentive problem. The financial rewards for winning races — particularly at the claiming and allowance levels where margins are small and purses matter to the bottom line — remain large enough relative to the probability of detection that some trainers will continue to take the risk. Detection technology also continues to lag behind drug development. Each new compound that enters use represents a window of time where it provides an advantage without reliable detection, which is exactly what Zilpaterol demonstrated at Louisiana Quarter Horse meets.
International consistency remains an issue as well. A horse trained in a jurisdiction with looser rules, imported for a major American race, may carry substances that cleared testing in its home country but would be prohibited under HISA. The protocols for managing international entries are significantly more complex than domestic testing, and elite international races continue to present regulatory gaps that sophisticated operations can exploit.
FAQs About Performance-Enhancing Drugs in Horse Racing
What are the most common performance-enhancing drugs in horse racing?
The most commonly detected PED categories are anabolic steroids (Stanozolol, Nandrolone), corticosteroids used outside permitted windows (betamethasone, dexamethasone), diuretics (furosemide/Lasix), and increasingly, muscle-growth beta-agonists like Zilpaterol in Quarter Horse racing. Blood-doping agents including EPO are also used but are less common at regional levels.
Is Lasix (furosemide) a performance-enhancing drug?
It is both a therapeutic drug and a source of performance advantage, which is why it divides the sport. Furosemide is a legitimate treatment for exercise-induced pulmonary hemorrhage (EIPH), a condition where horses bleed from the lungs during intense exercise. It is also a diuretic that causes horses to lose 20 to 30 pounds of body weight before a race and accelerates the clearance of other prohibited substances from urine. The US permits it with restrictions; most other countries ban it entirely.
What happened with Medina Spirit and the 2021 Kentucky Derby?
Medina Spirit, trained by Bob Baffert, won the 2021 Kentucky Derby but subsequently tested positive for betamethasone, a corticosteroid. The Kentucky Horse Racing Commission found a prohibited level of the substance in post-race testing. Medina Spirit was disqualified, Mandaloun was named the official winner, and Bob Baffert received a 90-day suspension and a $7,500 fine. The case accelerated the push for HISA’s uniform federal anti-doping program.
What is HISA and how does it change drug enforcement in horse racing?
HISA — the Horseracing Integrity and Safety Authority — established a uniform federal anti-doping and medication control program for all US Thoroughbred racing beginning in 2023. Before HISA, each of the 38 racing states operated under its own rules, creating significant inconsistency in permitted substances, withdrawal times, testing protocols, and penalties. HISA standardizes all of these nationally, meaning a trainer suspended under HISA cannot move to a different state’s jurisdiction to continue competing.
What is Zilpaterol and why is it dangerous for racehorses?
Zilpaterol is a beta-agonist originally developed to promote rapid muscle growth in cattle before slaughter. In horse racing, particularly Quarter Horse racing, it is being used to increase explosive muscle mass for short-distance sprints. An LSU veterinarian briefed at a Louisiana Racing Commission meeting described the drug as causing severe cardiovascular and musculoskeletal damage with horses that receive it likely to cause long term effects and possibly shorten lifespans. Zilpaterol is prohibited in racing but has appeared with increasing frequency in Louisiana Quarter Horse testing.
How are racehorses tested for performance-enhancing drugs?
Horses are tested post-race through blood and urine samples collected by racing commission officials in the test barn. Samples are sent to accredited laboratories for analysis using methods including gas chromatography, mass spectrometry, and immunoassay screening. Many commissions also conduct pre-race testing and out-of-competition testing under HISA. The specific substances tested and detection windows vary by compound — some clear a horse’s system within hours while others are detectable for weeks.
What penalties do trainers face for PED violations in horse racing?
Under HISA, penalties for prohibited substance violations range from fines and short suspensions for minor or first-time therapeutic medication violations to multi-year suspensions for intentional doping. At the Louisiana Racing Commission meeting described in this article, some trainers received five-year suspensions. Horses that test positive are disqualified and purse money is redistributed. Owners can also face fines and loss of racing privileges depending on the nature and severity of the violation.
Key Takeaways: Performance-Enhancing Drugs in Horse Racing
- The incentive problem outlasts every regulatory change — repeat offenders at racing commission meetings demonstrate that detection risk alone does not deter PED use when financial rewards remain high
- Anabolic steroids remain the most common category — their ability to mask injuries is as dangerous as their performance-enhancing effect
- Furosemide (Lasix) is both therapeutic and controversial — legitimate treatment for EIPH, but also a diuretic weight-loss agent and potential masking drug; the international consensus is moving against US race-day use
- Zilpaterol is the most alarming emerging threat — concentrated in Quarter Horse racing, causes severe health damage, and an LSU veterinarian’s assessment is that affected horses are likely to sustain permanent and long term health risks
- HISA’s uniform federal standard is the most significant structural change in American racing integrity — closes the jurisdiction arbitrage that allowed repeat offenders to move between state commissions
- Detection always lags drug development — each new compound creates a window where it provides an advantage before testing protocols catch up
About Miles Henry
Racehorse Owner & Author | 30+ Years in Thoroughbred Racing
Miles Henry (legal name: William Bradley) is a professional horseman based in Folsom, Louisiana. He holds Louisiana Racing License #67012 and has spent over three decades managing Thoroughbreds at premier tracks including Fair Grounds, Delta Downs, and Evangeline Downs.
Expertise & Hands-On Experience: Beyond the track, Miles has decades of experience in specialized equine care, covering everything from hoof health and nutrition to training protocols for Quarter Horses, Friesians, and Paints. Every guide on Horse Racing Sense is rooted in this “boots-on-the-ground” perspective.
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