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Diphenhydramine (brand name: Benadryl®, Vetadryl®, Banophen®, Genahist®, Diphenhist®, Unisom®, Sominex®) is an antihistamine used in cats, dogs, ferrets and other small mammals, birds, horses, and cattle to treat allergic reactions, motion sickness, and vomiting. It is also used as a mild sedative and is one of the therapies for mast cell tumors.
Its use in small and large animals to treat allergic reactions and other conditions is “off label” or “extra label”. Many drugs are commonly prescribed for off-label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions carefully, as they may be significantly different from those on the label.
This medication will take effect quickly, in about 1 to 2 hours, and improvement in clinical signs should follow.
If you miss a dose, give it as soon as you remember, and then continue with the regular dosing schedule. However, if it is almost time for the next dose, skip the missed dose and resume the regular dosing schedule. Do not give the pet two doses at once.
Diphenhydramine may cause the following side effects:
Diphenhydramine can alter the results of skin allergy testing; discontinue this medication at least 2 weeks before testing. This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.
Diphenhydramine should NOT BE USED in:
Diphenhydramine should be USED WITH CAUTION in pets that:
Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking. The following medications should be USED WITH CAUTION when given with diphenhydramine:
If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.
© Copyright 2025 LifeLearn Inc. Used and/or modified with permission under license. This content written by LifeLearn Animal Health (LifeLearn Inc.) is licensed to this practice for the personal use of our clients. Any copying, printing or further distribution is prohibited without the express written consent of LifeLearn. This content does not contain all available information for any referenced medications and has not been reviewed by the FDA Center for Veterinary Medicine, or Health Canada Veterinary Drugs Directorate. This content may help answer commonly asked questions, but is not a substitute for medical advice, or a proper consultation and/or clinical examination of your pet by a veterinarian. Please contact your veterinarian if you have any questions or concerns about your pet’s health. Last updated on Aug 7, 2024.
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6414 Smithville Road Smithville, Ontario L0R 2A0
Phone: (905) 957-3378
Email UsMonday: 8:00am – 6:00pm Tuesday: 8:00am – 6:00pm Wednesday: 8:00am – 6:00pm Thursday: 8:00am – 6:00pm Friday: 8:00am – 6:00pm Saturday: 8:00am – 12:00pm Sunday: Closed
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