US Equestrian has been monitoring the use of two commonly-used therapeutic medications – cetirizine (commonly known by the brand name of the human product Zyrtec), and methocarbamol (commonly known by the brand name Robaxin) -- taking into account member questions and concerns about those substances. 

Effective immediately, cetirizine will become a permitted substance and may be used in competition. Previously, cetirizine had been treated as a prohibited medication, meaning competitors had to file a Medication Report Form and halt use for at least 24 hours prior to competition. It has been treated as a Category IIa substance for penalty purposes; now, its use will no longer carry a penalty.  

Cetirizine is a second-generation antihistamine which is used routinely in horses to reduce allergic skin reactions or other seasonal allergies. It does not readily cross the blood/brain barrier and does not have apparent sedative effects on horses. Historically, cetirizine has been regulated the same way as first-generation antihistamines, which can cause drowsiness due to their ability to cross the blood/brain barrier and act on central receptors. Cetirizine is the active metabolite of hydroxyzine, which is a first generation of antihistamine.  While cetirizine will now be permitted, hydroxyzine will continue to be a prohibited substance.  Going forward, hydroxyzine will continue to be a prohibited substance but GR411 will apply, which requires a 24-hour withdrawal and the appropriate submission of a medication report form.   

“We’ve heard from our membership and understand the challenges of managing competition horses who struggle with hives and other types of allergy issues without their daily dose of cetirizine,” said Dr. Stephen Schumacher, Chief Veterinary Officer at US Equestrian. “While other regulatory bodies still treat this as a prohibited substance, given the changing environmental and climate factors that can irritate horses’ allergies, we felt this change was in the best interest of our horses.”  

The change in classification was approved by the USEF Veterinary Committee and the Board of Directors was notified of the update in July.  

Since cetirizine has been under review this year, any cases resulting from positive tests for cetirizine for the current competition year will be dropped, and any collected fines will be refunded for 2026 cases.  

Additionally, US Equestrian is revising its guidance on methocarbamol. After hearing from practitioners and others in the field with concerns about the metabolism of methocarbamol, there are now two recommended withdrawal timeframes for the drug in competition:  

• If methocarbamol is the only medication being given and the horse is not on any dietary supplement, the current  12-hour withdrawal recommendation should be used prior to competition.  

• If the horse is receiving any other medication or supplement while they are also being given methocarbamol, it is recommended  methocarbamol should be withdrawn at 24 hours prior to competition.  

The recommended dose for methocarbamol will remain the same – 500 mg/100 pounds of body weight either intravenously or orally.  

“We’ve heard some concerns that common medications or gastric supplements can change the rate at which methocarbamol is broken down by the horse’s body,” said Dr. Schumacher. “While we are not aware of any studies or literature supporting a connection that would cause a positive finding, we do hear our members’ concerns. It’s not financially or logistically practical to test every possible ingredient at every possible dose and combination alongside the recommended dose of methocarbamol, so until there is more research and data in this area, we are suggesting people back out their timeframe.”  

Methocarbamol is commonly thought of as a muscle relaxant, but it also creates side effects such as lethargy, muscle weakness, and ataxia. The rate at which a horse consumes feed containing an oral version of the drug, as well as the source of a compounded form of methocarbamol, can also impact the timing and dosing a horse receives before a competition. 

Learn more about the way methocarbamol works and additional considerations for use in this USEF Insider article.