Antihistamines for Dogs

Dogs with allergies may benefit from using antihistamines, such as Benadryl, which are often used as dog allergy medication to relieve symptoms such as itchiness. Read on and find out more about this dog allergy treatment option.

Besides corticosteroids, antihistamines are another type of dog allergy medication frequently used by veterinarians to relieve the itchiness in the allergic dog.

What is Histamine? How Do Antihistamines Work?

Antihistamines for Dogs Histamine is a chemical that is released by mast cells in an allergic dog's body in response to an exposure to allergens such as pollens, mold, house dust mites, etc. The released histamine locks onto histamine receptors (called H1 receptors) which are located on various cells in the dog's body. When that happens, the cells undergo biochemical changes and produce allergy symptoms such as itching, runny eyes and runny nose. Histamine receptors also release other chemicals that increase inflammation, resulting in inflammation of the skin in the allergic dog.

Antihistamines work by physically preventing (blocking) histamine from connecting with its histamine receptor, thus preventing the biochemical changes which produce the allergy symptoms.

How Effective Are Antihistamines To Control Dog Allergies?

Various studies on the effectiveness of antihistamines on dogs have been conducted with variable results. Specifically, about 10 to 30 percent of dogs have been found to show improvement after using antihistamines for their allergies.

Compared with corticosteroids, antihistamines are not as effective because antihistamines block only the histamine receptors on cells in the body. However, histamine is not the only chemical released by the mast cells. Other chemicals released can also cause allergy symptoms such as itching.

In addition, antihistamines for dogs work best when taken before allergy symptoms are evident - they are not so effective if taken when the allergic dog is already showing signs such as severe itching.

What Are Some Common Antihistamines for Dogs?

Some common antihistamines include:

  • Benadryl (diphenhydramine)
  • Atarax/Vistaryl (hydroxyzine)
  • Chlortrimeton (chlorpheniramine)
  • Tavist (clemastine)
  • Periactin (cyproheptadine)
  • Temaril (trimeprazine)

Different dogs react to antihistamines differently. If you are lucky, you may get an antihistamine that works for your dog first time round. On the other hand, there is also a possibility that none of the antihistamines work! Only by trial and error can we determine which antihistamine works best for our dog.

Are There Side Effects of Antihistamines on Dogs?

Antihistamines seem relatively safe to be used to treat dog allergies. The one major side effect is sedation - your dog may be sleepy when taking this medication. In some cases, sedation wears off in a few days.

Dogs with liver disease should use antihistamines with caution since antihistamines are metabolized by the liver. To strengthen the liver and support liver function, you may want to give a supplement that contains the herb milk thistle to your dog to help detoxify his liver while he is on antihistamines.

As well, dogs with the following conditions should not use antihistamines:

  • Glaucoma
  • Urinary retention disorders
  • Pregnancy


Dog Allergy Treatment

Besides antihistamines, there are other treatment options for dogs with allergies, such as corticosteroids, allergy shots, and of course natural remedies. Visit this page for information on some natural remedies that can relieve allergy itch. For other treatment options, click here.