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hy-DROX-eh-zeen - Pronunciation guide

Brand Names

  • Atarax
  • Hydroxyzine HCL: Oral Paste
  • Vistaril


Rx symbolHydroxyzine hydrochloride is an antihistamine used to treat allergic skin reactions in horses.  The drug works by competing with histamine for uptake at the histamine receptors on sensitive cells in the respiratory tract, intestines, blood vessels, and the skin, thereby counteracting the inflammation and itching of allergic reactions.


Hydroxyzine is given to treat hives, itchy or bumpy allergic skin reactions, and inflammation.  Antihistamines given orally take 20 to 45 minutes to begin counteracting the release of histamine from damaged cells and the resulting effect it has on the horse's body.  

Dosage and Administration

Prescription medicationHydroxyzine
Method Dosage
(click row for calculator)
Concentration Period Duration
Oral 0.5-1 mg/kg 50 mg/tablet 2 to 4 times daily NA
Intramuscular injection 0.5-1 mg/kg 50 mg/ml 2 to 4 times daily NA


  • Federal law restricts this drug to use by or on the order of a licensed veterinarian.
  • Extra-label use of drugs in treating animals is allowable only by licensed veterinarians within the context of a valid veterinarian-client-patient relationship, and does not include drug use in treating animals by the layman (except under the supervision of a licensed veterinarian).
  • Calculator is for educational purposes only. Follow your veterinarian's instructions regarding use of this, or any medication.

Side Effects

Sedation is the most common side effect.  Fine tremors, whole body tremors, excitement, and seizures are less common.


High doses of antihistamines can cause birth defects in laboratory animals.  Hydroxyzine should only be used in pregnant and lactating animals if the benefits outweigh the risks.  Animals may react differently to antihistamines and the dose of hydroxyzine should be tailored to the individual horse.

Hydroxyzine is not FDA approved for use in horses, although its use is considered accepted practice.  It is a prescription drug and U.S. federal law restricts this drug to use by or on the lawful written or oral order of a licensed veterinarian.

Hydroxyzine is prohibited or regulated in most sanctioned competitions.  It is important to consult the individual regulatory group.


Hydroxyzine has an additive effect when combined with other central nervous system depressant drugs, such as tranquilizers.


Overdose may cause increased sedation and increased risk of other side effects.


Hydroxyzine HLCHydroxyzine HLC

Hydroxyzine TabletsHydroxyzine Tablets



About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.