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Pets can have allergies just like their pet parents. That means that when you’re out together in nature and your dog gets stung by a bee, you’ll need reliable treatment ready in case they have an adverse reaction. You’ll also need medications on hand if your cat or dog has a history of food sensitivities or vaccination reactions. Benadryl for dogs and cats can be a big help in relieving symptoms like itching, swelling and pain when your pet has an allergic reaction.  

Read on to learn more about the use of this drug for pets, and visit the dog pharmacy and cat pharmacy to explore other allergy medications.  

What is Benadryl? 

Benadryl is a brand name for the generic drug diphenhydramine, which is classified as an antihistamine. You may recognize this type of medication from your own experiences with allergies—antihistamines like diphenhydramine help block the receptors in a pet’s body that typically respond to histamines. In turn, this can stop irritating symptoms like sneezing and hives that often arise when the body has an allergic reaction to something.  

More specifically, diphenhydramine is an ethanolamine-derivative antihistamine. It crosses the blood-brain barrier, which can make the drug more effective than other types of antihistamines. This drug is typically considered appropriate for dogs and cats, but you should only administer it to pets who have received a prescription from their veterinarian. You can find the human version over the counter, but it will probably be challenging to administer and measure accurately. Always consult your veterinarian before providing any form of diphenhydramine to cats or dogs. You can find more information on cat and dog health health and pet nutrition here at Petco.  

Reasons to use Benadryl (diphenhydramine) for pets 

While diphenhydramine is primarily given to pets who have allergies, it has a few other uses as well. Your veterinarian may recommend Benadryl for itching and other minor-to-moderate symptoms associated with everything from seasonal to environmental allergies. If your pet has a more serious or chronic allergy, however, a different medication may be required.  

Reasons to give this drug to pets include: 

  • Runny nose and eyes Sometimes pollen and other environmental allergens will affect your pet’s sinuses. This may lead to symptoms such as excess tears and a runny nose 

  • Sneezing Seasonal allergies can lead to sneezing in dogs and cats. Over time, uncontrolled sneezing can be uncomfortable  

  • Coughing Your dog or cat may begin to cough if their respiratory system becomes irritated or dried out by certain allergies  

  • Hives If your pet has an allergic reaction due to a bug bite, vaccine reaction or food sensitivity, they may experience hives. These should be treated right away so they don’t cause more severe skin problems or pain  

  • Itching When allergens affect the skin, your pet will instinctually scratch. Over time, this can cause the skin to break and become infected  

  • Mast cell tumors in dogs When mast cells in tumors degranulate, a large number of histamines are released in the body, and Benadryl can help relieve the resulting symptoms 

  • Anxiety The lethargic side effects of diphenhydramine can be ideal for helping calm pets with anxiety. However, in certain pets it can also have an excitatory effect, so talk to your vet before using

There may be other situations where your vet recommends Benadryl for animals. For instance, if your pet has one anaphylactic reaction to an allergen, your vet may recommend you keep the drug on hand for future allergic reactions.  

Benadryl dosage guidelines 

The proper Benadryl dosage for dogs and cats depends on their size. Your veterinarian will let you know how much to administer and when. The following guideline can be handy when deciding on a medication plan, but consult your vet before committing to a dosage.  

Dogs and cats 2 to 4 milligrams of medication per kilogram of body weight. 

Many pets can receive two to three doses in the above amounts per day. Keep in mind that aside from cats and dogs, most animals only take diphenhydramine in very specific circumstances. In ferrets, for example, the drug is primarily given to avoid a vaccine reaction.  

How to administer Benadryl

Benadryl liquid is available but isn’t always the easiest option for choosy or energetic pets. As a pet parent, you probably know that some dogs and cats won’t sit still for long enough to take medicine this way. Thankfully, the drug is also available in capsule and tablet forms for veterinary use. Administering the medication via capsule inside a treat may be the simplest way to give this medicine to your pet. For allergies that affect the skin, there’s also a Benadryl spray and ointment available that can help provide relief from itching and dryness. 


This drug can be taken with or without food. If the pills upset your dog’s or cat’s stomach, you may want to administer the next dose with soft food and water to see if that helps. If you miss a dose, don’t double up at the next scheduled administration time. Instead, either administer the missed dose a few hours late or skip it altogether and wait until the next dose.  When in doubt, consult your vet.

Possible Benadryl side effects  

There are a few possible side effects associated with diphenhydramine, and most occur within the first few hours of taking the medicine. The two most common side effects are drowsiness and dry mouth, but your pet may also retain some urine in some cases. Monitor your pet for about two hours after their first dose of diphenhydramine to make sure they are tolerating the medication well and aren’t experience more severe symptoms. Call your vet if your pet vomits or exhibits other, more severe side effects.  

Drug interactions  

Benadryl for cats and dogs may not be recommended if your pet is already taking other medications. Specifically, you may not want to administer this drug if your pet is already on an anticholinergic, certain antidepressants, sedatives, anesthetics or pain medications. Since diphenhydramine is known for inducing lethargy, your pet may not be a good candidate if they are already taking drugs that slow down their systems. Inform your vet if you are currently administering any natural remedies to your pet, including vitamins or supplements.  

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Reviewed by Dr. Whitney Miller, DVM, MBA, DACVPM

As Petco’s Chief Veterinarian, Dr. Miller is the lead veterinary subject matter expert, overseeing the company’s standards of excellence in animal care and welfare, growth in pet services and much more. Dr. Miller leads Petco’s medical team, supporting over 200 full-service hospitals and mobile vaccination clinics operating in over 1,000 Petco Pet Care Centers nationwide