Side Effects of Benadryl for Cats

side effects of benadryl for cats_canna-pet

Many humans take Benadryl for allergic reactions without a second thought and the drug has even become popular for use with dogs, but is it safe for your feline friend? As an antihistamine, Benadryl is simply the brand name for the drug. The active ingredient, diphenhydramine, is the same in both the name brand and generic versions of the drug.

Although Benadryl is considered an over-the-counter medication and does not require a valid prescription for humans, it can be used safely by felines under your vets supervision. That said, you should always consult with your veterinarian before giving your cat any human medications as they can come with some serious side effects when not administered properly.

Uses of Benadryl for Cats

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When it comes to cat allergies, Benadryl is most often prescribed for itchy or allergic skin reactions, vaccine reactions, or bug bites. Your vet may also permit the use of Benadryl as a mild sedative for your cat when traveling.

Antihistamines counteract histamine, which is a chemical released during an allergic reaction that causes inflammation and itchiness. When histamines attach to H-1 receptors on the small blood vessels and smooth muscles, the vessels widen causing inflammation and itchiness, while muscles around the airways contract –  resulting in breathing difficulties. The diphenhydramine in Benadryl works by blocking H-1 receptors.

Administering Benadryl to Cats

If your vet prescribes Benadryl for your cat, ask if he or she can provide a liquid version of the drug. Using a syringe and liquid Benadryl is typically the easiest way to orally administer a dose to your cat. However, many cats will refuse to take the drug if they do not like the odor or taste. In this case, ask your vet about a compounding pharmacy.

Compounding pharmacies are able to flavor the drug with the liquid of chicken, fish, or other taste that may be more appealing to your cat. If your vet prescribed pills, these can also be flavored by a compounding pharmacy. You might also try mixing the drug, liquid or pill, in with your cat’s food to see if he will ingest it during his meal.

When giving your cat any sort of drug, be sure to follow your vet’s instructions explicitly. Pay close attention to the size of each dose and their frequencies and administer the drug as long as instructed, even if symptoms dissipate. Stopping the medication before it is time may lengthen the time it takes for your cat to recover or cause him to relapse.

Side Effects of Benadryl for Cats

Even when you follow your vets instructions for administering Benadryl to your cat, the following side effects may occur:

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If your cat experiences any of the above side effects while taking Benadryl, notify your vet for further instruction. If too much medicine is administered, overdoses can lead to seizures, coma, difficulties breathing, or even death. These complications illustrate why it is extremely important to follow your veterinarian’s instructions.

You will also want to use caution if your cat is on other medications. Be sure your vet is aware of other drugs your cat is on beforehand as it can have known interactions with the following:

  • Central Nervous System Depressants – Used to treat anxiety in cats
  • Amitraz – Used as a tick prevention method
  • Furazolidon – Prescribed as an antibacterial agent
  • Selegiline – Used to treat cognitive dysfunction, or senility
  • Epinephrine – Treatment for anaphylaxis, a severe and sudden allergic reaction
  • Heparin Sodium or Calcium – Used to treat diseases associated with blood clotting such as disseminated intravascular coagulation and thromboembolic disease
  • Warfarin Sodium – Prescribed to treat and prevent blood clots

If you are currently administering any of the above to your cat, your veterinarian should be able to suggest another solution for allergies in cats. As with all medications, use caution and discuss any concerns with your veterinarian. This will help ensure that your cat is receiving the best care possible.


  1. “Benadryl for Dogs and Cats.” PetMD, Accessed 8 Nov. 2017.
  2. “PetMD.” Can You Give a Cat Benadryl? Accessed 8 Nov. 2017.
  3. “Benadryl for Cats.” VetInfo, Accessed 8 Nov. 2017.
  4. “Benadryl for Cats.” The Pet Step, Accessed 8 Nov. 2017.
  5. Crosby, Janet. “What’s Benadryl® For, and Can You Give It to Cats and Dogs?” The Spruce Pets, Accessed 8 Nov. 2017.

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