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How Do I Choose The Best Antihistamine For Dogs?

Susana Bradford
January 12, 2024
March 15, 2023
7 minute read
Updated By
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March 15, 2023
August 29, 2023
7 minute read
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Ease your dog's allergies with effective remedies to alleviate intense scratching and hives. Restore your pet's well-being and vibrant life.

If you are an emotional support dog owner, you know they can be at risk of occasional allergy problems. Unfortunately, allergies are common among dogs and can cause the dog to be extremely uncomfortable and unable to complete the tasks it needs to provide you with its support. 

Allergies can make your dog's life miserable. If your dog is an emotional support animal, the allergies can make them less valuable to you as they'll be battling their conditions. Allergies are also frustrating to dog owners as there is no single treatment for all allergies. Furthermore, individual pets react differently to different treatments.

The good news is that you can use antihistamines to deal with dog allergies. In addition, they are inexpensive and are easily found over the counter.

What is an Allergy?

In simple terms, an allergy in humans is the body's reaction to an allergen. Whenever allergens enter the body and come in contact with mast cells (a type of white blood cell), the cells' histamine receptors trigger a reaction to expel the allergens.

The same happens when your dog is exposed to allergens.

What are the Common Allergy-Causing Substances?

Before we jump into how to remedy allergies in dogs, let's look at what causes the allergies. Dog Allergies are categorized into:

  1. Environmental allergies
  2. Food allergies
  3. Flea allergies

Environmental Allergies

Seasonal irritants cause environmental or seasonal allergies in dogs. These irritants are usually more prominent during spring and summer and include:

  • Grass Pollen
  • Weed Pollen
  • Tree Pollen
  • Dust Mites
  • Mold and Mildew

Seasonal allergies usually affect dogs in their earlier years and cause itchiness around dog faces, paws, and armpits.

Flea Allergies in Dogs

Flea allergies are common among dogs and differ from allergies to bites. In this case, the allergy is caused by the flea saliva deposited on the dog's skin. After a few deposits, the saliva starts causing itchiness that irritates the dog.

Food Allergies in Dogs

An ingredient in food causes food allergies. This is because dogs' digestive systems react to various foods, especially sources of proteins. Some other food triggers for dogs include chocolate, wheat, and eggs.

What are the Symptoms of Dog Allergies?

The general symptoms usually associated with allergies in dogs include:

  • Excessive self-scratching, chewing, licking, and rubbing on a rough surface to show itchiness
  • Hives
  • Hair loss
  • Sneezing
  • Diarrhea
  • Vomiting and excessive gas
  • Red skin
  • Swelling 
  • Skin infection (red bumps or pimples)
  • Dry cough
  • Increased odor and discharge from the infected area
  • Excessive dandruff

Whenever you see such signs from your dog, you must contact your dog's veterinarian for instructions and advice on how to help correctly.

What are Antihistamines for Dogs?

Antihistamines are drugs used to treat symptoms of allergies. The drugs help when the immune system produces too much histamine, signaling there is an allergy present.

Common antihistamines used as canine medication include diphenhydramine, chlorpheniramine, clemastine fumarate, and hydroxyzine. Each dog will react differently to a given medicine. For guidance, take your dog to be examined by a veterinarian.

What Antihistamines Help Dogs With Allergies?

Here are some of the antihistamines to help your dog battle allergies.


Diphenhydramine can be an effective antihistamine for dogs for acute reactions, such as those that occur in response to vaccination, blood transfusion, or bee stings. It is also used to treat itchiness and swelling. Treatment with diphenhydramine can also mitigate the effects of airborne allergens on dogs.

Veterinarians usually recommend 1 mg of diphenhydramine per pound of the dog's weight.


Another commonly used antihistamine for dogs is chlorpheniramine. Like diphenhydramine, its efficacy is highest when used to treat acute allergic responses to things like snake and insect bites and reactions to vaccinations and blood transfusions. In addition, chlorpheniramine can help treat mast cell tumors, which are growths composed of histamine, the substance that provokes allergic reactions. The dosage advised by veterinarians is usually three tablets per day.

Clemastine Fumarate

Also recommended as an antihistamine for dogs is clemastine fumarate. It is one of the most effective antihistamines for dogs with itchy skin. Clemastine fumarate is a comparatively expensive antihistamine, but many dog owners choose it for its efficacy. In addition, it is administered twice daily, less often than most other canine antihistamines.


Hydroxyzine is an antihistamine that tends to be effective in treating itchy skin. It's also helpful in treating acute allergic reactions to bites, stings, and vaccinations. Dosing depends on the individual dog and must be recommended by a veterinarian. However, dog owners often treat their pets with hydroxyzine because of its availability in small tablets that are easy to administer to canine patients.

Zyrtec (Cetirizine)

Zyrtec has become a common antihistamine for treating dog allergies thanks to its convenient dosing schedule. Additionally, while dogs react to antihistamines differently, Zyrtec has had a higher response rate than others.

The drug has minimal side effects, although some pets do become drowsy.

The dosing schedule is also much more suitable, with dogs weighing over 10 lbs getting a single 10mg tablet once daily. Dogs weighing less than 10 lbs can have half of a 10mg tablet once daily.

Omega-3 Fatty Acids

The effectiveness of antihistamines for dogs is thought to be heightened when it is supplemented with omega-3 fatty acids. These substances help reduce the inflammation involved in allergic reactions. In addition, omega-3 fatty acids combined with antihistamines are particularly effective for treating itchy skin.

Before and During Administration

It is essential to see a doctor before taking any drugs, but it is also important to seek a veterinarian's advice before administering antihistamines to your ESA dog. This is especially important if the dog is on other medication or supplements.

Be cautious when dealing with a pregnant dog, a dog susceptible to seizures, or certain other health conditions. It is also vital to administer antihistamines for a week if you are in the trial stage to find the best for your dog.

While most antihistamines are okay for dogs, it is critical to ensure that the medicine contains no harmful ingredients. Ingredients such as pseudoephedrine cause allergies in dogs.

You can also hide the medicines in your dog's favorite treats like Pill Pockets, or a bit of canned food helps improve acceptance. Then, if your dog has no problem with the drugs, you can feed them directly.

What are the Side Effects of Antihistamines?

Side effects of antihistamines include sedation and the reduction of nausea. Therefore, veterinarians sometimes recommend antihistamines for dogs that suffer from motion sickness or require tranquilizing. Other side effects of antihistamines can include seizures, diarrhea, and liver damage. Since antihistamines are strong medicines, it is best to consult a veterinarian before administering them to dogs.

What Other Therapies Are Available? 

There are other medications apart from antihistamines that you can use to treat allergies in your dog.

Anti-Inflammatory Therapy

Some anti-inflammatory drugs, like corticosteroids, will quickly stop any allergic reactions from taking shape. You can also use fatty acid supplementation to improve how anti-inflammatory drugs respond.

Some alternatives block specific chemical signals associated with the itch in dogs. Such drugs include oral medications, such as oclacitinib, and long-acting injections. Your vet can help you choose the best option.

Shampoo Therapy

Cleaning or bathing your dog can help relieve itchiness and inflamed skin. When you use hypoallergenic shampoo to wash your dog, its properties help soothe the skin and subsequently help fight symptoms of allergies.

The shampoo also helps remove allergens from the dog's coating to avoid absorption through the skin. You can also go for shampoos with anti-inflammatory ingredients that have more benefits.

Hyposensitization or Desensitization Therapy

When you go to the veterinarian, they may conduct an allergy test to identify the offending antigens. In this case, if the antigens are known, you can opt to give the dog an injection serum or allergy shots.

This is done weekly to help reprogram or desensitize the immune system. The process works differently among the dogs, with others seeing a higher success rate than others.

Meet the author:
Susana Bradford

Susana is an avid animal lover and has been around animals her entire life, and has volunteered at several different animal shelters in Southern California. She has a loving family at home that consists of her husband, son, two dogs, and one cat. She enjoys trying new Italian recipes, playing piano, making pottery, and outdoor hiking with her family and dogs in her spare time.

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