Key takeaways:
Benadryl (diphenhydramine) is used off-label in dogs for allergic reactions, allergic skin skin disease, mast cell tumors, and motion sickness.
The most common side effects of Benadryl include lethargy and sedation.
Benadryl can have interactions with other medications, and dosages are different in dogs than in people. Pet owners should check with their veterinarian to make sure Benadryl is a safe option for their dog.
When a person feels hay fever coming on, they may take Benadryl (diphenhydramine). When pets experience allergies, it’s almost always in the form of an itchy skin condition.
Veterinarians have several options for managing allergic reactions in dogs. Benadryl is an over-the-counter tool that vets recommend to help treat allergies.
Learn about how Benadryl is used in dogs with allergies and more.
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Benadryl for dogs at a glance
Common names | Diphenhydramine (Benadryl, Vetadryl) |
What it treats | Allergic reactions, anaphylaxis, allergic skin disease, motion sickness |
How it comes (forms) | Tablets, capsules, oral solutions, injectables |
Typical dosage | 2-4 mg per kilogram of body weight every 8 to 12 hours |
Common side effects | Lethargy, sedation, constipation, dry mouth, urinary retention |
Average cost |
What is Benadryl for dogs, and how does it work?
Benadryl (diphenhydramine) is an antihistamine. Benadryl works by blocking histamine from binding to its receptors. Histamine is an important chemical that causes widespread inflammation during an allergic reaction.
The medication is FDA approved for humans but is used off-label in dogs. There is also a pet-specific brand of Benadryl called Vetadryl.
What is Benadryl used for in dogs?
Benadryl is used to treat allergic and inflammatory reactions, including:
Medication reactions
Vaccination reactions
Bee stings
Transfusion reactions
Insect bites
Benadryl is sometimes prescribed for dogs with itchy skin due to allergies. But Benadryl is more useful in allergies causing hives than for actually reducing itchiness.
Dogs with mast cell tumors are often prescribed antihistamines like diphenhydramine. The cells of mast cell tumors contain histamine. When the histamine is released, it can cause widespread inflammation. Benadryl keeps the histamine from binding to its receptors.
Benadryl is sometimes recommended for motion sickness in dogs. This is because it has an anti-nausea side effect.
Could your dog have allergies? Read up on the most common symptoms of seasonal allergies in dogs.
Dog motion sickness: If your pup gets queasy in the car, here are ways to combat your dog’s motion sickness.
Safe OTC meds: Don’t assume human over-the-counter medications are safe for dogs. Learn which ones you should never give your pup.
What is the dosage of Benadryl for dogs, and how is it given?
Dosing for Benadryl in dogs is different from dosing in humans. Pet owners should not assume the dose they take is the same their dog will take.
When Benadryl is given by mouth, the dosage is generally 2 mg to 4 mg per kilogram of body weight every 8 to 12 hours.
When a veterinarian gives injectable diphenhydramine directly into a muscle, the dose is 0.5 mg to 2 mg per kilogram of body weight.
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Pet owners should speak with a veterinarian before giving Benadryl to their dog.
What are the common side effects of Benadryl in dogs?
The most common side effects of Benadryl in dogs include:
Lethargy
Sedation
Dry mouth
Urinary retention
Occasionally, some dogs experience vomiting, diarrhea, and loss of appetite after taking Benadryl.
What are the most serious risks of Benadryl for dogs?
Benadryl is generally safe for dogs. Pet owners should use products that contain diphenhydramine as the only active ingredient. Combination products may be dangerous for dogs.
More serious risks occur with high overdoses of Benadryl. These include:
High body temperature (hyperthermia)
Tremors
High heart rate (tachycardia)
Agitation
Fatal overdoses are rare.
Does Benadryl interact with other dog medications?
Benadryl can interact with many medications that dogs take, including:
Amantadine
Atropine or glycopyrrolate
Metoclopramide or cisapride
Monoamine oxidase inhibitors (MAOIs) like amitraz or selegiline
Neostigmine or pyridostigmine
Potassium supplements
Specific diuretics, like hydrochlorothiazide
Tricyclic antidepressants, like amitriptyline or clomipramine
What should you do if your dog misses a dose of Benadryl?
If you miss giving your dog a dose of Benadryl, give the missed dose as soon as possible. Then continue with the regular dosage schedule provided by your veterinarian.
If your dog’s symptoms are worsening despite taking Benadryl, contact your veterinarian. Do not administer a second dose without speaking to your veterinarian.
The bottom line
Benadryl is most useful for sudden allergic reactions in dogs. The medication is not FDA approved for use in dogs. Benadryl is often prescribed off-label for dogs with allergies, mast cell tumors, or motion sickness.
Sedation and lethargy are the most common side effects in dogs. Pet owners should work with their veterinarian to determine if Benadryl is a safe option for their dog.
Why trust our experts?
References
Brooks, W. (2023). Diphenhydramine (Benadryl, Vetadryl, Banophen, Diphenhist). Veterinary Partner.
Gamperl, S., et al. (2021). In vitro effects of histamine receptor 1 antagonists on proliferation and histamine release in canine neoplastic mast cells. Veterinary Medicine and Science.
Merck Veterinary Manual. (n.d.). Antihistamine dosages.
Pegasus Laboratories. (2022). Vetadryl 10, 30- diphenhydramine hydrochloride tablet [package insert].
Shipstone, M. (2022). Antihistamines for integumentary disease in animals. Merck Veterinary Manual.
Worth, A. C., et al. (2016). Diphenhydramine exposure in dogs: 621 cases (2008–2013). Journal of the American Veterinary Medical Association.
