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Zyrtec Dosage Calculator for Dogs

Zyrtec is a brand of cetirizine. The dose for dogs is 1 to 2 mg/kg once a day, or 10 to 20 mg per dog, which is about 0.5 mg per pound. Most dogs get 10 mg (one tablet) once a day, capped at 20 mg. Cats get a flat 5 mg per cat. Use only plain cetirizine, and ask your vet before giving any medicine.

By Sikander Malik · Updated October 16, 2026 · Sources

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Plain cetirizine (Zyrtec) for dogs, from the Merck Veterinary Manual and the AAHA 2023 guidelines. Cats use a flat dose; see the note below.

Ask your vet before giving any medicine, and confirm the amount for your dog.

Typical dose (start low)

1.5× 10 mg tablets

= 15 mg (about 1.3 mg/kg), once a day.

Full range11 mg–20 mg (1.5–2 tablets)
Never exceed20 mg per dose

Only plain cetirizine. Never Zyrtec-D or any product with a decongestant (pseudoephedrine or phenylephrine). Check liquids and children’s formulas for xylitol and other active ingredients.

Estimates only, not veterinary advice. Reviewed against the Merck Veterinary Manual antihistamine table and the AAHA 2023 allergic skin disease guidelines, October 2026. Medical disclaimer.

Zyrtec for cats (a flat dose, not by weight)

Cats: 5 mg per cat (half a 10 mg tablet) once a day. Vets may use up to 10 mg per cat. This is a per-cat dose, not by weight (AAHA 2023, Table 8; Merck Veterinary Manual). Be cautious in cats with kidney disease, which is common in older cats, and ask your vet first.

If you think your pet had too much

Call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435 (a consultation fee may apply), or go to your nearest emergency vet. A plain cetirizine overdose is usually mild, but a Zyrtec-D overdose (pseudoephedrine) is an emergency.

How much Zyrtec can I give my dog?

Zyrtec is a brand of cetirizine, an antihistamine. The published dose for dogs is 1 to 2 mg/kg once a day (AAHA 2023 guidelines), or 10 to 20 mg per dog (Merck Veterinary Manual), which is about 0.5 mg per pound. The calculator leads with that lower amount and caps the result at 20 mg per dose, so a big dog is not given a very large amount. Always confirm with your vet first.

Dog Zyrtec doses by weight
Dog cetirizine dose by weight
WeightDose once a day10 mg tablets
10 lb5 mg0.5 tablet
15 lb10 mg1 tablet
20 lb10 mg–15 mg1–1.5
30 lb15 mg–20 mg1.5–2
44 lb20 mg2 tablets
60 lb20 mg2 tablets
80 lb20 mg2 tablets
100 lb20 mg2 tablets
1–2 mg/kg once a day, capped at 20 mg per dose. From about 44 lb (20 kg) up, the dose holds at 20 mg (2 tablets); your vet may adjust it.
Sources: Merck Veterinary Manual (1 mg/kg or 10–20 mg/dog) and AAHA 2023, Table 3 (1–2 mg/kg q24h).

Check the box: plain cetirizine only

Use a product whose only active ingredient is cetirizine. Never give a combination product with a decongestant, such as Zyrtec-D or anything listing pseudoephedrine or phenylephrine; those can be dangerous for pets. Check liquids and children’s formulas for xylitol, which is toxic to dogs. Read the active ingredient panel every time.

Who should not take it

Talk to your vet before giving cetirizine if your pet:

  • has kidney or liver disease (cetirizine is cleared by the kidneys);
  • is pregnant or nursing;
  • is a cat with kidney disease, which is common in older cats;
  • is already on other medicines, until your vet checks for interactions.

From the cetirizine precautions in the Merck Veterinary Manual and Plumb’s Veterinary Drug Handbook.

Overdose signs

Too much plain cetirizine is usually mild, but watch for:

  • heavy drowsiness, or the opposite, restlessness;
  • drooling or an upset stomach;
  • with a Zyrtec-D product, a racing heart, agitation and tremors, which is an emergency.

If you see these, or gave a Zyrtec-D product, call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435 right away.

Questions owners ask

How much Zyrtec can I give my dog?
The published dose is 1 to 2 mg/kg once a day (AAHA 2023), or 10 to 20 mg per dog (Merck Veterinary Manual), which is about 0.5 mg per pound. A 10 to 20 lb dog is usually 5 to 10 mg once daily, and most larger dogs get 10 mg, up to 20 mg. We cap the result at 20 mg per dose. Check with your vet first.
How much Zyrtec for a cat?
Cats get a flat 5 mg per cat (half a 10 mg tablet) once a day, and vets may use up to 10 mg per cat (AAHA 2023, Table 8). This is a per-cat dose, not by weight. Be careful in older cats with kidney disease, and ask your vet before giving it.
Can I use Zyrtec-D?
No. Never give Zyrtec-D or any product with a decongestant (pseudoephedrine or phenylephrine), which can be dangerous for pets. Only use a product whose single active ingredient is cetirizine, and check liquids and children’s formulas for xylitol, which is toxic to dogs.
How often can I give it?
Once a day for both dogs and cats. Cetirizine is a once-daily antihistamine, so do not give it more often unless your vet tells you to. If it is not helping after a few days, ask your vet rather than increasing the dose.
What should I use Zyrtec for?
Vets sometimes suggest cetirizine for mild itching or seasonal allergies in dogs. It will not fix a serious allergic reaction. For facial swelling, hives, or trouble breathing, call your vet or an emergency clinic now rather than waiting on an antihistamine.
What if I gave too much?
A plain cetirizine overdose is usually mild, causing drowsiness or restlessness, but call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435 to be sure. If you gave a Zyrtec-D product, which contains a decongestant, treat it as an emergency and call right away.

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Sources

Estimates only, not veterinary advice. Reviewed against the Merck Veterinary Manual antihistamine table and the AAHA 2023 allergic skin disease guidelines, October 2026. Medical disclaimer.