Zyrtec for Dogs

Written By Emily Gantt
Published: 03/13/2021Updated: 04/13/2023
Veterinary reviewed by Michele K.
Zyrtec for Dogs

Zyrtec is an over-the-counter human allergy medication sometimes given to dogs with atopic dermatitis or mild to moderate environmental allergies. Vets may recommend Zyrtec for dogs who scratch excessively, are sensitive to insect bites, or have dermatitis. 


Zyrtec is available in in 5- and 10-milligram tablets. It can be given either every 24 hours for atopic dermatitis, or every 12 hours for allergy symptoms.

Here's the recommended Zyrtec dosage for dogs based on their weight:

  • Less than 10 pounds: 2.5 milligrams (half of a 5-milligram pill or a quarter of a 10-milligram pill)
  • 10–50 pounds: One 10-milligram tablet
  • 50+ pounds: Up to two 10-milligram tablets

Zyrtec also comes in a liquid form that must be dosed with a syringe or dropper. This form can be drizzled over pet food or squirted directly into the pet's mouth. Liquid Zyrtec may be easier to dose out for smaller dogs since the tablets are small and can be difficult to cut evenly.

Got questions or concerns about the correct dosage of Zyrtec for dogs? Use Wag! Vet Chat to connect with a veterinary expert fast. (Average response time = 6 minutes!)


Zyrtec's active ingredient, cetirizine, is closely related to hydroxyzine, a powerful antihistamine that's sometimes used before surgeries to help patients relax. Zyrtec is considered a second-generation antihistamine and doesn't cause drowsiness like first-generation alternatives.

So how does Zyrtec stack up to other antihistamines? One study of dogs with atopic dermatitis found that Zyrtec reduced itching in 18% of the dogs studied. The only side effects noted in this study were vomiting in two dogs after taking the drug.

In another, more successful study, dogs who took Zyrtec before being injected with histamine had less inflammation around the injection site than those who didn't receive the drug. This experiment had a 100% efficacy rate in the small 8-dog study group. 

A separate study of 12 dogs injected with histamines found that the active ingredient in Zyrtec was notably more effective than Benadryl at minimizing the body's immune response.

Side effects

Side effects from Zyrtec in dogs are rare, but occasionally some dogs experience:


Experts do not recommend Zyrtec for pregnant or breastfeeding dogs since there is little research on its use in these groups. Some veterinarians will still prescribe Zyrtec for pregnant and nursing dogs on an individual basis if the benefits outweigh the risks. 

Never give Zyrtec to dogs who are allergic to antihistamines, especially those with cetirizine or hydroxyzine in them. This may cause a life-threatening reaction called anaphylactic shock

Use this medication carefully in dogs with kidney or liver problems since it can stay in their system for much longer than healthy dogs. Stop treatment immediately if your dog begins showing signs of urine retention or other severe side effects. 

Giving an antihistamine inappropriately may mask signs of other disease, so it is best to ask you veterinarian if this medication is right for your dog.  

Drug interactions

  • Opioids (such as codeine, hydrocodone, or morphine)
  • Anti-anxiety or sleep medications (such as alprazolam, lorazepam, zolpidem, diazepam, and clonazepam)
  • Muscle relaxers (such as carisoprodol andcyclobenzaprine)
  • Oral or topical antihistamines (such as chlorpheniramine and diphenhydramine)
  • Pseudoephedrine (found in nasal decongestants)

Allergic reactions and sensitivity

It sounds strange, but pets can be allergic to allergy medications, including Zyrtec. Tell your vet if your pet's allergy symptoms worsen or if they have signs of anaphylaxis like trouble breathing or swelling of the face. 

Symptoms of a severe drug reaction include:

Frequently asked questions about Zyrtec for dogs

Should I give Zyrtec to my dog with a meal?

Food does not affect Zyrtec's efficacy, so feel free to give it to your pup with or without food. 

What should I do if I miss a dose of Zyrtec for my dog?

  • For dogs taking Zyrtec twice daily: give the next dose at the usual time.

  • For dogs taking Zyrtec once daily: give the medication when you think of it, and resume the normal dosage time the next day.

  • Avoid "doubling up" to make up for missed doses. 

Is it normal for Zyrtec to make my dog tired?

Zyrtec is one of the few antihistamines that do not cause drowsiness for most dogs, though there are some exceptions. If Zyrtec makes your dog sleepy, try giving it to them before bedtime to see if that helps their energy levels during the day.

How should I store Zyrtec for dogs?

Keep your pup's Zyrtec in a cool, dry area away from bright light. Liquid Zyrtec is shelf-stable while sealed. While it may be tempting to put liquid Zyrtec in the refrigerator after opening, doing so can actually make it less effective.

Can I give my dog Zyrtec-D?

Never give your dog Zyrtec-D since it contains powerful decongestants that can harm dogs. While one pill might seem innocuous, there's data that shows a single dose of Zyrtec-D can kill or inflict irreversible harm to small dogs.

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