Side Effects of Zyrtec for Dogs

side effects of zyrtec for dogs_canna-pet

Dogs can suffer from allergies just as much as people can, and in fact, they often do. While drugs like Benadryl may be helpful in some instances, Benadryl isn’t always effective in treating a dog’s allergy symptoms.

These days, vets are turning to using a second-generation drug called cetirizine hydrochloride, more commonly known as Zyrtec. Zyrtec may be prescribed in both liquid and pill form, although it is most often given as a pill. Zyrtec should never be administered without the permission and supervision of a licensed veterinary professional.

What is Zyrtec?

Zyrtec is a second-generation antihistamine typically prescribed for human use, although increasingly, vets are prescribing it for use in the treatment of canine allergies as well. It is not FDA approved for use in animals however, so it is considered in off label or “extra” label prescription. This means that it is being prescribed for something it has not been specifically approved by the FDA to be used for.

A dog’s body will release a chemical called histamine during an allergic or an inflammatory response. When this chemical is released, it travels through the body looking for histamine receptors within the cells.

H1 histamine receptors can affect the smooth muscles and small blood vessels in a dog’s body. With a dog’s small blood vessels, H1 histamine can cause them to dilate and leak fluid. With a dog’s smooth muscles, H1 histamine can cause a restriction of a dog’s airways, which can trigger difficulties with breathing.

Once histamines have attached to the respective histamine receptors, your dog can experience reactions like itching and swelling. Some dogs may suffer from watery eyes or a runny nose. In more severe cases, a dog can experience labored breathing and even go into anaphylactic shock.

H2 histamine receptors on the other hand, can affect a dog’s stomach acid secretions and cause ulcers, as well stimulate a dog’s heart rate.

Drugs like Zyrtec block the histamine effect that occurs when they attach to those histamine receptors, which is why Zyrtec and drugs like it, are called “anti” histamine medications.

Most histamine blocking drugs work to either bind to H1 receptors or H2 receptors. Very few drugs will work on both types of histamine receptors. How an antihistamine works in your dog’s body will depend on which histamine receptor the drug is intended to bind with.

In the case of Zyrtec, it is intended to work with the H1 histamine receptors, to help reduce or prevent symptoms like swelling or itching in dogs. However, Zyrtec will do nothing for stomach acid secretions or symptoms related to heart rate.

What is Zyrtec Used for in Dogs?

zyrtec for dogs_canna-pet

For most dogs, Zyrtec is used to treat itching and other symptoms of an allergic reaction in dogs. Usually these allergic reactions are related to related to atopic dermatitis and allergic contact dermatitis.

One type of allergic response is related to inhalants, and the other is related to something your dog comes into contact with topically. Both trigger allergic reactions that affect your dog’s skin, like itching, inflammation, hives, and swelling.

Signs of Allergies in Your Dog

Like their human owners, dogs can be allergic to just about anything. However, there are some allergens that seem to be more common and more prevalent than others.

These common allergens in dogs include:

  • Fleas (or more specifically) flea saliva from flea bites
  • Food and food additive allergies
  • Environmental allergens, such as dust mites, pollen, grasses and weeds

Dogs suffering from allergies may also display symptoms such as:

  • Skin redness and irritation
  • Swelling
  • Excessive itching
  • Rubbing their face and muzzle frequently
  • Chewing their paws or legs

Sometimes, when symptoms are extremely severe or are left untreated, your dog may experience hair loss, or suffer from secondary skin infections like a bacterial or yeast infection.

If your dog experiences a very severe allergic response, he can develop hives or even go into anaphylactic shock. If you think your dog is in anaphylactic shock, treat it as an emergency and get your dog to the vet immediately for treatment. Anaphylactic shock is dangerous and can be life-threatening.

Dogs that have developed atopy may exhibit symptoms such as:

  • Skin irritations
  • Frequent licking
  • Frequent biting
  • Chewing on their paws
  • Rubbing their face and muzzle
  • Shaking their head
  • Scratching, especially in the groin and armpit area
  • Skin that appears “thick”

In cases of atopy, Zyrtec appears to be particularly useful as a treatment option.

zyrtec for dogs side effects_canna-pet

Dosages of Zyrtec for Dogs

In most cases, your vet will prescribe Zyrtec tablets to be given to your dog once a day by mouth. A typical oral dose is based on a dog’s size, starting at 1mg of cetirizine per kilogram of weight.

However, this is only an estimation, so you need to see your vet for proper dosing. Never just give your dog Zyrtec from a bottle of over-the-counter medication that is intended for human use. It’s also important never to give your dog Zyrtec-D.

The “D” might as well stand for death, as giving your dog Zyrtec-D can be lethal. The D in Zyrtec-D stands for pseudoephedrine and is administered to humans as a decongestant medication. However, it can greatly overstimulate a dog’s central nervous system (CNS) as well as their heart. This can lead to high blood pressure, canine seizures, and even death.

Side Effects of Zyrtec in Dogs

When dogs are given Zyrtec in the right dosage, side effects usually aren’t too worrisome. In some cases, side effects may be non-existent. Regardless, Zyrtec is a relatively safe medication to give your dog, as long as you are doing it under the care of your vet and not simply giving them medication you bought over the counter.

Overdoses on Zyrtec are rare and most likely will not be dangerous unless you have accidentally given your dog Zyrtec-D and not the regular Zyrtec. When testing of Zyrtec was done on animals, the test subjects were given amounts up to 220 times above the normal human dose, with no serious adverse side effects.

Antihistamines in general tend to only work in about 30% of dogs it is given to. Unfortunately, about 25% of those dogs end up suffering from negative effects.

Also, antihistamines are not a cure, nor do they help heal your dog of the underlying condition that is causing their allergy. Antihistamines are like a band-aid measure, and they are designed to only treat symptoms, not cure the cause.

The most common side effect reported with Zyrtec for dogs appears to be sleepiness, which tends to fade the longer your dog is on the drug, as their body adjusts to the medication. In rare cases, a dog may experience a heavy sedation effect while on Zyrtec, although this appears to be more common when the drug is used on smaller dogs and/or at higher doses than typically recommended.

Other side effects that have been reported from using Zyrtec in dogs includes:

Precautions When Giving Zyrtec to Dogs

dog zyrtec_canna-pet

Because Zyrtec can cause canines to retain urine, giving it to dogs with kidney problems could potentially make existing conditions worse.

The same goes for dogs that suffer from liver problems, as Zyrtec could exacerbate the issue. Dogs that are pregnant should probably steer clear of Zyrtec as well, as there haven’t been enough studies yet that show Zyrtec can be safely given to a pregnant dog.

Additionally, dogs that are nursing should not be given Zyrtec as the drug can be passed along to the pups through their milk, and nursing puppies are much too young for such medications.

There are some dogs that may display a hypersensitivity to antihistamines, and develop an allergic reaction to the drug intended to treat such reactions! If that sounds like it could be your dog then it is wise to steer clear of giving them Zyrtec or similar antihistamine drugs like Benadryl for dogs.

Also, please note that if your dog is currently on any other medications, especially drugs that they may take on a regular basis (or even on a sporadic basis), make sure your vet is aware of them. This will allow your vet to assess potential complications, and they can advise you on any potential drug interactions that could occur between your dog’s current medications and Zyrtec.

Natural Alternatives to Giving Zyrtec to Your Dog

Sometimes your dog may be unable to take Zyrtec, either because of drug interactions, pre-existing health conditions, or simply because you prefer to give your dog natural remedies over synthetic ones. Fortunately, there are some natural alternatives to giving your dog Zyrtec.

One option that many people use for dogs who suffer from allergies is hemp nutrition, such as Canna-Pet®. Canna-Pet® provides veterinarian-recommended, safe products that customers use for a variety of dog ailments including allergies, seizures, cancer, pain, anxiety, and more!  

As you can see, there may be some side effects of Zyrtec for dogs if not given in the proper dosage, or if your dog is not given the proper formula (I.e. Zyrtec-D… the big NO!). But in most cases, the effects will be relatively mild. In cases where the side effects are too much for your dog, you can try some of the natural alternatives for dog allergies listed here.

The most important thing you can do though, is listen to your dog and the cues they are giving you. No dog owner wants to see their pet suffer, whether it’s from allergies or medication side effects. Treating allergies is really a case of trial and error, and only you can be certain on what appears to be beneficial for your dog, and what is not.


  1. “Zyrtec for Dogs: A Word of Warning.” Honest Paws, Accessed 27 Nov. 2017.
  2. “Zyrtec For Dogs.” Veterinary Place, Accessed 27 Nov. 2017.
  3. “Cetirizine (Zyrtec®) for Dogs and Cats.” PetPlace, 7 May 2018, Accessed 27 Nov. 2017.
  4. “Zyrtec For Dogs: Dosage, Side Effects, And More [6 Key Factors].” Ultimate Home Life, 15 June 2018, Accessed 27 Nov. 2017.
  5. “Should You Give Your Dog Zyrtec?”, 7 Sept. 2018, Accessed 27 Nov. 2017.

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