Cetirizine vs Benadryl: what's the difference?
How Cetirizine and Benadryl compare: what each is for, how it works, side effects and cost, side by side.
Last updated: October 2026 · 2 sources · see sources
Side by side
| Cetirizine | Benadryl | |
|---|---|---|
| Generic name | Cetirizine | Diphenhydramine |
| Brand names | Zyrtec, Reactine | Benadryl, Vetadryl |
| For | Dogs and cats | Dogs and cats |
| Prescription | Over the counter (ask your vet first) | Over the counter (ask your vet first) |
| Used for | Vets use it for itching from skin allergies, hives and insect bite reactions, and sometimes for respiratory allergy signs. [1] | Used for allergic reactions, motion sickness and vomiting, and as a mild sedative. It is also part of treatment for mast cell tumors. [2] |
| How it works | It is an antihistamine. It blocks histamine, one of the chemicals that causes itching and swelling. [1] | It is an older antihistamine that blocks histamine and also causes drowsiness. [2] |
| Common side effects | Usually mild. Rarely vomiting or drooling; sleepiness in small dogs and cats at higher doses. [1] | Tiredness, excitement (especially in cats), dry mouth, trouble urinating, vomiting, diarrhea and low appetite. [2] |
| Use with care | Never use the combination product with pseudoephedrine (Zyrtec-D), which is dangerous for pets. Ask your vet before giving it, even though it is sold over the counter. [1] | Use caution in pets with glaucoma, prostate enlargement, heart disease or high blood pressure. Many human products add other drugs that pets should not have, so check with your vet first. Stop it two weeks before skin allergy testing. [2] |
| Full guide | Cetirizine (Zyrtec) guide | Benadryl guide |
Key differences
On the basics they are alike: same kind of animal, same way to get them. The differences are in how they work and what else they cover, shown in the table above.
Which one is right for my pet?
That is a call for your vet. They weigh your pet's age, weight, other health problems, other medicines and what you can realistically give at home.
Switching from Cetirizine to Benadryl is common, but do it only with your vet's plan.
Common questions
What is the difference between Cetirizine and Benadryl?
Both are antihistamines vets sometimes suggest. Benadryl is the older one and tends to cause drowsiness; cetirizine is used mostly for itch, hives and bite reactions.
Is Cetirizine better than Benadryl?
Neither is better for every pet. Your vet chooses based on your pet's species, age, health history, other medicines and what you can manage at home.
Can my pet take Cetirizine and Benadryl together?
Only if your vet says so. Some medicines in the same family should not be combined, and others are often used together. Always check before adding or switching.
Do Cetirizine and Benadryl need a prescription?
Cetirizine: Many forms are sold without a prescription. Still, check with your vet first. Pet doses and safe products are not the same as for people. Benadryl: Many forms are sold without a prescription. Still, check with your vet first. Pet doses and safe products are not the same as for people.
Related
This page is general information for planning, not veterinary advice. Talk to your vet about your own pet.