At several of the Hunter/Jumper barns I’ve worked at over the years, I’ve been asked to administer Medroxyprogesterone acetate (also known as MPA or “Depo”) to a couple of the show, pleasure, and riding horses. The Food and Drug Administration (FDA) has approved the use of Depo-Provera in humans but not in horses. A compounded form of Depo is used in horses. Depo is most commonly used as a horse form of birth control; it is believed to suppress the estrus cycle in mares and will block the hormones involved in the heat cycle to prevent crazy mood swings and/or behavioral issues. Some barns will use it on geldings or stallions who act “studish” or exhibit stallion-like behavior.
Depending on how it is prescribed or recommended for use by your veterinarian, Depo is given as an intramuscular (IM) injection either weekly, bi-weekly, or monthly. There has been no conclusive research done on appropriate dosing for Depo and therefore the dosage and amount given can vary throughout the horse world. There are also beliefs that Depo has an anti-anxiety effect on horses, which has not been proven in studies. Several top veterinarians believe this behavioral effect might be true, but there is no scientific data to support this theory. Depo comes in a normal or double strength dosage thus reading the labels on any medication you administer is always of utmost importance. Not doing so when handling a medication could lead to serious complications or death.
There are several studies that have shown Depo has no effect on estrus suppression in mares, but there are equine veterinarians who disagree with this. Some argue that they see more suppression of the heat cycle when horses are on Altrenogest, or Regumate. Unfortunately, the downfall about Regumate is that it is difficult to administer because it is dangerous for women to handle. Altrenogest now comes in an injectable form, also administered IM, however it is significantly more expensive than oral Regumate.
So, knowing that Depo has the potential to be ineffective, you can imagine how a majority of the Hunter/Jumper horse show world was confused in 2017 when USEF attempted to ban Depo from being used in show horses. USEF tried to restrict the use of Depo because they said that it was being used in high quantities to quiet horses. They had little to no concrete or credible evidence to back this theory up.
This sent a majority of the show world into uproar. There was so much opposition to this proposed rule change that the USEF held a workshop on March 13th, 2017 to speak with professionals about their concerns and the proposed rule changes surrounding Depo. This was live streamed online on the USEF website so if members could not attend, they could observe and submit suggestions/questions to be read at the workshop.
Dr. Steven Schumacher, a veterinarian who spoke at the workshop, said that there is a possibility that Depo reacts with the GABA receptors in the horse’s brain to create a “tranquilizing effect,” thus altering a horse’s behavior to better improve performance. Again, there is no definitive study on this theory.
USEF bans any medications that they feel enhance a horse’s performance, which is what led to their insistence on a ban of Depo. But many professionals argued that NSAIDs (also known as Non-Steroidal Anti-Inflammatory Drug) also enhance a horse’s performance and help the horses who need a little assistance perform their daily jobs better. Therefore, the reason for this immediate ban of Depo didn’t make sense—why was this specifically being targeted but nothing else? It seemed no one could accurately answer that question. Sissy Wickes, a prominent trainer and R-judge, argued that the United States Olympic Committee (USOC) does not perceive this drug to be performance-enhancing because female human athletes are allowed to be on Depo-Provera and compete. It also worried many professionals that banning Depo could lead to people finding more dangerous drugs to use or lunging horses more frequently for longer periods of time.
USEF stated they would take suggestions and questions for a week after the workshop while they decided the next step in the process of banning Depo. But the only change that occurred at that time was that starting September 1st, 2017, trainers needed to fill out an MPA Disclosure Form before every show, stating which horse is on Depo, the amount being administered, the source of the medication, the reason for the use of Depo, administration route, and last administration date. This would allow for the USEF Board of Directors to assess the data collected from members on each form and would lead to them determining further action into a ban or regulation on Depo use. It would also help them determine accurate withdrawal times for Depo.
Canada banned the use of Depo because they observed that Depo was being administered in their country with increased frequency and in high dosages. Equestrian Canada also bans any medication or drug that they believe “either directly or indirectly affects the performance of a horse.” They felt that because of the higher doses of Depo being administered, Depo must have been improving the horse’s behavior and therefore putting them at an advantage over their competition. This led to their rule change and is why they now test for Depo.
In 2019, the U.S. saw several unexpected Depo-related deaths in horses. In the last three years, 23 equine fatalities have been attributed to Depo use. Reports have stated that the drug was properly administered intramuscularly but was still fatal to the horse. It was determined that these horses died from anaphylaxis, which is an allergic reaction to Depo.
This led to a follow-up meeting of the USEF Depo panel in October of this year to review a petition by numerous veterinarians requesting that USEF ban the substance. The Panel determined that Depo has no therapeutic use in competition horses, as it does not interrupt estrus in mares, as was originally thought. Additionally, Depo is not approved by the United States Food and Drug Administration (FDA) for use in horses. As a result, the Panel voted unanimously to recommend that Depo was added to the list of USEF prohibited substances.
Starting December 1, 2019, MPA in horses competing at USEF-licensed competitions will be prohibited. However, due to the length of time involved for MPA to clear a horse’s system, sanctions for a positive test result will begin on June 1, 2020. The USEF has classified Depo as a Category III substance which has a penalty range starting at a 3-6-month suspension and a fine of $3,000-$6,000 for a first offense.
Sissy Wickes Powerpoint Presentation shown at USEF workshop
USEF Board of Directors Prohibits the Use of Medroxyprogesterone Acetate
Medroxyprogesterone Acetate Found to Have No Therapeutic Use in Competition Horses and has Been Linked to Anaphylaxis and Fatalities; Ban Effective
December 1, 2019
From the US Equestrian Communications Department